{"id":4824,"date":"2026-06-03T06:24:30","date_gmt":"2026-06-03T05:24:30","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/cracking\/"},"modified":"2026-10-25T12:09:24","modified_gmt":"2026-10-25T12:09:24","slug":"cracking","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/cracking\/","title":{"rendered":"Cracking"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-cracking-page\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n      --soft-yellow: #fff8e6;\n      --red: #c81e1e;\n      --gold: #c9973a;\n      --green: #3f8f46;\n      --grey-text: #667085;\n      --body-text: #1f2937;\n      --border: rgba(28, 36, 75, 0.14);\n      --shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n      --inner-shadow: 0 10px 26px rgba(28, 36, 75, 0.08);\n      font-family: Poppins, Arial, sans-serif;\n      color: var(--navy);\n      background: #ffffff;\n    }\n\n    .ols-revision-page * {\n      box-sizing: border-box;\n    }\n\n    .ols-main {\n      min-width: 0;\n      max-width: 970px;\n    }\n\n    .ols-breadcrumbs {\n      display: flex;\n      flex-wrap: wrap;\n      gap: 8px;\n      margin: 10px 0 22px;\n      font-size: 15px;\n      color: var(--grey-text);\n    }\n\n    .ols-breadcrumbs a,\n    .ols-breadcrumbs span {\n      color: var(--grey-text);\n      text-decoration: none;\n      font-weight: 600;\n    }\n\n    .ols-breadcrumbs a {\n      transition: color 0.2s ease, text-decoration-color 0.2s ease;\n    }\n\n    .ols-breadcrumbs a:hover {\n      color: var(--blue);\n      text-decoration: underline;\n      text-underline-offset: 3px;\n    }\n\n    .ols-title-card,\n    .ols-note-card,\n    .ols-h5p-card,\n    .ols-related-card,\n    .ols-faq-card {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 28px;\n      box-shadow: var(--shadow);\n      padding: 34px;\n      margin-bottom: 24px;\n      overflow: hidden;\n    }\n\n    .ols-title-card {\n      background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);\n    }\n\n    .ols-title-card h1 {\n      margin: 0 0 18px;\n      font-size: clamp(36px, 5vw, 58px);\n      line-height: 1.08;\n      font-weight: 800;\n      letter-spacing: -0.04em;\n      color: #111827;\n    }\n\n    .ols-page-intro {\n      font-size: 19px;\n      line-height: 1.7;\n      font-weight: 300;\n      color: var(--body-text);\n      margin: 0 0 22px;\n    }\n\n    .ols-badges {\n      display: flex;\n      flex-wrap: wrap;\n      gap: 12px;\n      margin-bottom: 22px;\n    }\n\n    .ols-badge {\n      display: inline-flex;\n      align-items: center;\n      padding: 9px 14px;\n      border-radius: 999px;\n      background: #ffffff;\n      border: 1px solid var(--border);\n      font-size: 15px;\n      font-weight: 600;\n      color: var(--navy);\n    }\n\n    .ols-note-card.soft {\n      background: linear-gradient(135deg, #ffffff 0%, var(--soft-red) 100%);\n    }\n\n    .ols-note-card.purple {\n      background: linear-gradient(135deg, #ffffff 0%, var(--soft-purple) 100%);\n    }\n\n    .ols-note-card.green {\n      background: linear-gradient(135deg, #ffffff 0%, var(--soft-green) 100%);\n    }\n\n    .ols-note-card.yellow {\n      background: linear-gradient(135deg, #ffffff 0%, var(--soft-yellow) 100%);\n    }\n\n    .ols-note-title {\n      display: flex;\n      align-items: center;\n      gap: 14px;\n      margin-bottom: 20px;\n    }\n\n    .ols-note-icon {\n      width: 52px;\n      height: 52px;\n      border-radius: 16px;\n      background: var(--navy);\n      color: #ffffff;\n      display: grid;\n      place-items: center;\n      font-size: 24px;\n      font-weight: 800;\n      flex-shrink: 0;\n    }\n\n    .ols-note-title h2,\n    .ols-h5p-card h2,\n    .ols-related-card h2,\n    .ols-faq-card h2 {\n      margin: 0;\n      font-size: clamp(28px, 3.5vw, 42px);\n      line-height: 1.15;\n      font-weight: 800;\n      color: #111827;\n      letter-spacing: -0.03em;\n    }\n\n    .ols-note-card p,\n    .ols-note-card li {\n      font-size: clamp(15px, 1.25vw, 17px);\n      line-height: 1.65;\n      font-weight: 300;\n      color: var(--body-text);\n    }\n\n    .ols-h5p-card p,\n    .ols-related-card p,\n    .ols-faq-card p {\n      font-size: clamp(15px, 1.3vw, 18px);\n      line-height: 1.65;\n      font-weight: 300;\n      color: var(--body-text);\n    }\n\n    .ols-note-card strong,\n    .ols-h5p-card strong,\n    .ols-related-card strong,\n    .ols-faq-card strong {\n      font-weight: 700;\n      color: var(--navy);\n    }\n\n    .ols-note-card ul,\n    .ols-note-card ol {\n      margin: 0;\n      padding-left: 22px;\n    }\n\n    .ols-key-box {\n      margin-top: 20px;\n      background: var(--soft-green);\n      border: 1px solid rgba(63, 143, 70, 0.25);\n      border-radius: 20px;\n      padding: 18px 20px;\n    }\n\n    .ols-key-box p {\n      margin: 0;\n      font-weight: 400;\n      color: var(--navy);\n    }\n\n    .ols-warning-box {\n      margin-top: 20px;\n      background: #fff7f7;\n      border: 1px solid rgba(200, 30, 30, 0.22);\n      border-left: 5px solid var(--red);\n      border-radius: 20px;\n      padding: 18px 20px;\n    }\n\n    .ols-warning-box p {\n      margin: 0;\n      font-weight: 400;\n      color: var(--navy);\n    }\n\n    .ols-definition-box {\n      background: linear-gradient(135deg, #ffffff, var(--soft-purple));\n      border: 2px dashed rgba(122, 62, 157, 0.35);\n      border-radius: 24px;\n      padding: 26px;\n      margin-top: 22px;\n      display: grid;\n      grid-template-columns: 1fr;\n      gap: 16px;\n      align-items: center;\n    }\n\n    .ols-definition-circle {\n      width: 105px;\n      height: 105px;\n      border-radius: 50%;\n      background: linear-gradient(135deg, #9b59b6, #6f3d96);\n      color: white;\n      display: grid;\n      place-items: center;\n      font-size: 22px;\n      font-weight: 800;\n      text-align: center;\n      margin: 0 auto;\n    }\n\n    .ols-figure-card {\n      margin: 26px 0 4px;\n      border: 1px solid var(--border);\n      border-radius: 26px;\n      overflow: hidden;\n      background: #ffffff;\n      box-shadow: var(--inner-shadow);\n    }\n\n    .ols-figure-image {\n      width: 100%;\n      min-height: 330px;\n      display: flex;\n      align-items: center;\n      justify-content: center;\n      background: #ffffff;\n      padding: 20px;\n    }\n\n    .ols-figure-image img {\n      max-width: 100%;\n      height: auto;\n      display: block;\n      border-radius: 18px;\n    }\n\n    .ols-figure-caption {\n      padding: 20px 24px 22px;\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n      border-top: 1px solid var(--border);\n    }\n\n    .ols-figure-caption p {\n      margin: 0;\n      color: #5f6b85;\n      font-size: clamp(15px, 1.25vw, 17px);\n      line-height: 1.6;\n      font-weight: 300;\n      font-style: italic;\n    }\n\n    .ols-table-wrap {\n      overflow: hidden;\n      border-radius: 22px;\n      border: 1px solid var(--border);\n      background: #ffffff;\n      margin-top: 18px;\n    }\n\n    .ols-table {\n      width: 100%;\n      border-collapse: collapse;\n      table-layout: fixed;\n    }\n\n    .ols-table th {\n      background: var(--navy);\n      color: #ffffff;\n      padding: 16px;\n      text-align: left;\n      font-size: clamp(14px, 1.2vw, 17px);\n      font-weight: 600;\n      overflow-wrap: anywhere;\n      word-break: normal;\n    }\n\n    .ols-table td {\n      padding: 16px;\n      border-bottom: 1px solid var(--border);\n      font-size: clamp(14px, 1.15vw, 16px);\n      line-height: 1.45;\n      color: var(--body-text);\n      vertical-align: top;\n      overflow-wrap: anywhere;\n      word-break: normal;\n    }\n\n    .ols-table tr:last-child td {\n      border-bottom: none;\n    }\n\n    .ols-h5p-card {\n      background: linear-gradient(135deg, #ffffff 0%, #f7f0ff 100%);\n    }\n\n    .ols-h5p-frame {\n      margin-top: 22px;\n      padding: 18px;\n      border-radius: 24px;\n      background: #ffffff;\n      border: 1px solid var(--border);\n      box-shadow: inset 0 0 0 1px rgba(28, 36, 75, 0.03);\n    }\n\n    .ols-fraction-grid {\n      display: grid;\n      grid-template-columns: repeat(2, minmax(0, 1fr));\n      gap: 16px;\n      margin-top: 20px;\n    }\n\n    .ols-fraction-pill {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 16px 18px;\n      box-shadow: var(--inner-shadow);\n    }\n\n    .ols-fraction-pill strong {\n      display: block;\n      margin-bottom: 4px;\n      font-size: 17px;\n      color: var(--navy);\n    }\n\n    .ols-fraction-pill span {\n      display: block;\n      font-size: 15px;\n      line-height: 1.55;\n      color: var(--body-text);\n      font-weight: 300;\n    }\n\n    .ols-faq-card {\n      background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);\n    }\n\n    .ols-faq-list {\n      display: grid;\n      gap: 14px;\n      margin-top: 20px;\n    }\n\n    .ols-faq-item {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 18px 20px;\n      box-shadow: var(--inner-shadow);\n    }\n\n    .ols-faq-item h3 {\n      margin: 0 0 8px;\n      font-size: 18px;\n      line-height: 1.35;\n      color: var(--navy);\n    }\n\n    .ols-faq-item p {\n      margin: 0;\n    }\n\n    .ols-related-grid {\n      display: grid;\n      grid-template-columns: repeat(3, minmax(0, 1fr));\n      gap: 16px;\n      margin-top: 18px;\n    }\n\n    .ols-related-item {\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 18px;\n      background: #ffffff;\n      color: var(--navy);\n      text-decoration: none;\n      font-weight: 600;\n      line-height: 1.5;\n      transition: transform 0.2s ease, box-shadow 0.2s ease;\n    }\n\n    .ols-related-item:hover {\n      transform: translateY(-2px);\n      box-shadow: 0 10px 22px rgba(28, 36, 75, 0.08);\n    }\n\n    @media (max-width: 1050px) {\n\n      .ols-main {\n        max-width: none;\n      }\n\n      .ols-related-grid {\n        grid-template-columns: repeat(2, minmax(0, 1fr));\n      }\n    }\n\n    @media (max-width: 760px) {\n\n      .ols-title-card,\n      .ols-note-card,\n      .ols-h5p-card,\n      .ols-related-card,\n      .ols-faq-card {\n        padding: 24px 18px;\n        border-radius: 22px;\n      }\n\n      .ols-note-title {\n        align-items: flex-start;\n      }\n\n      .ols-figure-card {\n        border-radius: 22px;\n      }\n\n      .ols-figure-image {\n        min-height: 230px;\n        padding: 14px;\n      }\n\n      .ols-figure-caption {\n        padding: 18px;\n      }\n\n      .ols-table-wrap {\n        border-radius: 20px;\n        overflow: hidden;\n      }\n\n      .ols-table,\n      .ols-table thead,\n      .ols-table tbody,\n      .ols-table th,\n      .ols-table td,\n      .ols-table tr {\n        display: block;\n        width: 100%;\n      }\n\n      .ols-table thead {\n        display: none;\n      }\n\n      .ols-table tr {\n        border-bottom: 1px solid var(--border);\n        background: #ffffff;\n      }\n\n      .ols-table tr:last-child {\n        border-bottom: none;\n      }\n\n      .ols-table td {\n        display: grid;\n        grid-template-columns: minmax(120px, 38%) minmax(0, 1fr);\n        gap: 12px;\n        align-items: start;\n        border-bottom: 1px solid rgba(28, 36, 75, 0.08);\n        padding: 14px;\n        overflow-wrap: anywhere;\n      }\n\n      .ols-table td:last-child {\n        border-bottom: none;\n      }\n\n      .ols-table td::before {\n        content: attr(data-label);\n        font-weight: 700;\n        color: var(--navy);\n        overflow-wrap: anywhere;\n      }\n    }\n\n    \/* OLS saved author profile block *\/\n.ols-author{\n    display:flex;\n    align-items:center;\n    gap:20px;\n    padding:28px;\n    border-radius:28px;\n    background:linear-gradient(135deg,#ffffff 0%,#f8fbff 100%);\n    border:1px solid rgba(28,36,75,0.12);\n    box-shadow:0 18px 45px rgba(28,36,75,0.10);\n  }\n\n  .ols-author-avatar-img{\n    width:92px;\n    height:92px;\n    border-radius:50%;\n    object-fit:cover;\n    object-position:center;\n    flex-shrink:0;\n    border:4px solid #ffffff;\n    box-shadow:\n      0 14px 32px rgba(28,36,75,0.18),\n      0 0 0 1px rgba(28,36,75,0.10);\n    transition:\n      transform 0.25s ease,\n      box-shadow 0.25s ease;\n  }\n\n  .ols-author:hover .ols-author-avatar-img{\n    transform:scale(1.04);\n    box-shadow:\n      0 20px 42px rgba(28,36,75,0.22),\n      0 0 0 1px rgba(28,36,75,0.10);\n  }\n\n  .ols-author-content{\n    min-width:0;\n  }\n\n  .ols-author-title{\n    margin:0 0 4px;\n    font-size:clamp(24px,3vw,34px);\n    line-height:1.15;\n    font-weight:700;\n    color:#1C244B;\n    letter-spacing:-0.03em;\n  }\n\n  .ols-author-description{\n    margin:0;\n    font-size:17px;\n    line-height:1.7;\n    font-weight:300;\n    color:#667085;\n  }\n\n  .ols-linkedin-pill{\n    display:inline-flex;\n    align-items:center;\n    justify-content:center;\n    gap:10px;\n    margin-top:16px;\n    padding:11px 18px;\n    border-radius:999px;\n    background:linear-gradient(135deg,#0A66C2,#004182);\n    color:#ffffff !important;\n    text-decoration:none;\n    font-size:14px;\n    line-height:1;\n    font-weight:700;\n    letter-spacing:0.01em;\n    box-shadow:0 10px 22px rgba(10,102,194,0.24);\n    position:relative;\n    overflow:hidden;\n    transition:\n      transform 0.22s ease,\n      box-shadow 0.22s ease;\n  }\n\n  .ols-linkedin-pill::before{\n    content:\"\";\n    position:absolute;\n    top:0;\n    left:-120%;\n    width:100%;\n    height:100%;\n    background:linear-gradient(\n      120deg,\n      rgba(255,255,255,0) 0%,\n      rgba(255,255,255,0.28) 50%,\n      rgba(255,255,255,0) 100%\n    );\n    transition:left 0.7s ease;\n  }\n\n  .ols-linkedin-pill:hover{\n    color:#ffffff !important;\n    transform:translateY(-3px) scale(1.03);\n    box-shadow:\n      0 16px 34px rgba(10,102,194,0.34),\n      0 0 0 6px rgba(10,102,194,0.10);\n  }\n\n  .ols-linkedin-pill:hover::before{\n    left:120%;\n  }\n\n  .ols-linkedin-icon{\n    width:18px;\n    height:18px;\n    display:block;\n    flex-shrink:0;\n  }\n\n  @media (max-width:640px){\n\n    .ols-author{\n      align-items:flex-start;\n      padding:22px 18px;\n      border-radius:22px;\n    }\n\n    .ols-author-avatar-img{\n      width:72px;\n      height:72px;\n    }\n\n    .ols-author-title{\n      font-size:24px;\n    }\n\n    .ols-author-description{\n      font-size:15px;\n    }\n  }\n\n  .ols-linkedin-pill:hover, .ols-linkedin-pill:focus { color:#ffffff !important; }\n\n\n\n    \/* Image hover zoom and CSS-only fullscreen lightbox effect\n       Front-end robust version: does not depend on JavaScript running. *\/\n    body:has(.ols-cracking-page) .wp-site-blocks,\n    body:has(.ols-cracking-page) .site,\n    body:has(.ols-cracking-page) .site-main,\n    body:has(.ols-cracking-page) .content-area,\n    body:has(.ols-cracking-page) .entry-content,\n    body:has(.ols-cracking-page) .wp-block-post-content,\n    body:has(.ols-cracking-page) .elementor,\n    body:has(.ols-cracking-page) .elementor-section,\n    body:has(.ols-cracking-page) .elementor-container,\n    body:has(.ols-cracking-page) .elementor-widget-container {\n      overflow: visible !important;\n    }\n\n    .ols-cracking-page,\n    .ols-cracking-page .ols-main,\n    .ols-cracking-page .ols-title-card,\n    .ols-cracking-page .ols-note-card,\n    .ols-cracking-page .ols-h5p-card,\n    .ols-cracking-page .ols-related-card,\n    .ols-cracking-page .ols-faq-card,\n    .ols-cracking-page .ols-figure-card,\n    .ols-cracking-page .ols-figure-image {\n      overflow: visible !important;\n    }\n\n    .ols-cracking-page .ols-figure-card {\n      position: relative;\n      z-index: 20;\n    }\n\n    .ols-cracking-page .ols-figure-image {\n      position: relative;\n      z-index: 30;\n    }\n\n    .ols-cracking-page .ols-cracking-image-link {\n      display: inline-block;\n      max-width: 100%;\n      line-height: 0;\n      cursor: zoom-in;\n      position: relative;\n      z-index: 40;\n      overflow: visible !important;\n      text-decoration: none;\n    }\n\n    .ols-cracking-page img.ols-zoomable-img,\n    .ols-cracking-page img.ols-cracking-zoom-img {\n      cursor: zoom-in !important;\n      transform-origin: center center;\n      transition: transform 0.28s ease, box-shadow 0.28s ease, filter 0.28s ease;\n      position: relative;\n      z-index: 45;\n      will-change: transform;\n    }\n\n    .ols-cracking-page .ols-cracking-image-link:hover img.ols-cracking-zoom-img,\n    .ols-cracking-page img.ols-zoomable-img:hover,\n    .ols-cracking-page img.ols-cracking-zoom-img:hover {\n      \/* Transform is calculated dynamically by the safe viewport hover-zoom script. *\/\n      box-shadow: 0 26px 70px rgba(28, 36, 75, 0.28);\n      filter: saturate(1.03) contrast(1.02);\n      z-index: 9999;\n    }\n\n    .ols-cracking-page .ols-lightbox-overlay,\n    #ols-cracking-lightbox {\n      position: fixed !important;\n      inset: 0 !important;\n      z-index: 999999 !important;\n      display: none;\n      align-items: center;\n      justify-content: center;\n      padding: 32px;\n      background: rgba(12, 18, 38, 0.88);\n      backdrop-filter: blur(6px);\n      text-decoration: none;\n      cursor: zoom-out;\n    }\n\n    .ols-cracking-page .ols-lightbox-overlay.is-open,\n    #ols-cracking-lightbox:target {\n      display: flex !important;\n    }\n\n    .ols-cracking-page .ols-lightbox-img,\n    #ols-cracking-lightbox .ols-lightbox-img {\n      max-width: min(96vw, 1280px);\n      max-height: 90vh;\n      width: auto;\n      height: auto;\n      object-fit: contain;\n      border-radius: 22px;\n      background: #ffffff;\n      box-shadow: 0 30px 90px rgba(0, 0, 0, 0.35);\n      cursor: default;\n    }\n\n    .ols-cracking-page .ols-lightbox-close,\n    #ols-cracking-lightbox .ols-lightbox-close {\n      position: fixed;\n      top: 22px;\n      right: 24px;\n      width: 48px;\n      height: 48px;\n      border: 0;\n      border-radius: 999px;\n      background: #ffffff;\n      color: #1C244B;\n      font-size: 34px;\n      line-height: 48px;\n      font-weight: 300;\n      cursor: pointer;\n      box-shadow: 0 14px 34px rgba(0, 0, 0, 0.22);\n      text-align: center;\n      text-decoration: none;\n      transition: transform 0.2s ease, box-shadow 0.2s ease;\n    }\n\n    .ols-cracking-page .ols-lightbox-close:hover,\n    #ols-cracking-lightbox .ols-lightbox-close:hover {\n      transform: scale(1.06);\n      box-shadow: 0 18px 44px rgba(0, 0, 0, 0.28);\n    }\n\n    @media (max-width: 760px) {\n      .ols-cracking-page .ols-cracking-image-link:hover img.ols-cracking-zoom-img,\n      .ols-cracking-page img.ols-zoomable-img:hover,\n      .ols-cracking-page img.ols-cracking-zoom-img:hover {\n        transform: none !important;\n        box-shadow: none;\n        filter: none;\n      }\n\n      .ols-cracking-page .ols-lightbox-overlay,\n      #ols-cracking-lightbox {\n        padding: 18px;\n      }\n\n      .ols-cracking-page .ols-lightbox-close,\n      #ols-cracking-lightbox .ols-lightbox-close {\n        top: 14px;\n        right: 14px;\n      }\n    }\n\n    \/* Generic safe viewport hover zoom\n       Enlarges each marked image as much as possible without exceeding the browser viewport.\n       The script keeps the zoomed image approximately 3vw\/3vh away from the viewport edges. *\/\n    .ols-cracking-page .ols-safe-hover-img {\n      position: relative;\n      z-index: 45;\n      cursor: zoom-in !important;\n      transform-origin: center center;\n      transition:\n        transform 0.28s ease,\n        box-shadow 0.28s ease,\n        filter 0.28s ease,\n        z-index 0s linear;\n      will-change: transform;\n    }\n\n    .ols-cracking-page .ols-safe-hover-img.is-hover-zoomed {\n      z-index: 9999 !important;\n      box-shadow: 0 26px 70px rgba(28, 36, 75, 0.28);\n      filter: saturate(1.03) contrast(1.02);\n    }\n\n    @media (max-width: 760px) {\n      .ols-cracking-page .ols-safe-hover-img,\n      .ols-cracking-page .ols-safe-hover-img.is-hover-zoomed {\n        transform: none !important;\n        box-shadow: none !important;\n        filter: none !important;\n      }\n    }\n\n<\/style>\n\n  <aside class=\"ols-sidebar\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Topic 6 Organic Chemistry I<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/\">Introduction to Organic Chemistry<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/iupac-rules\/\">IUPAC Rules<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/alkene\/\">Alkene<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/alcohol\/\">Alcohol<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/halogenoalkanes\/\">Halogenoalkanes<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/aldehyde\/\">Aldehyde<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/ketone\/\">Ketone<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/carboxylic-acid\/\">Carboxylic Acid<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/ester\/\">Ester<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/isomerism\/\">Isomerism<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/\">Alkanes<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/\">Alkanes from Crude Oil<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/fractional-distillation\/\">Fractional Distillation<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/cracking\/\">Cracking<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/reforming\/\">Reforming<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/\">Alkanes as Fuel<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/combustion\/\">Combustion<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/oxides-of-sulfur\/\">Oxides of Sulfur<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/oxides-of-nitrogen\/\">Oxides of Nitrogen<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/catalytic-converter\/\">Catalytic Converter<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/alternative-fuel\/\">Alternative Fuel<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/\">Reactions of Alkanes<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/free-radical-substitution\/\">Free Radical Substitution<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/initiation\/\">Initiation<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/propagation\/\">Propagation<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/termination\/\">Termination<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/further-substitution\/\">Further Substitution<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/\">Alkenes<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/alkene-bonding\/\">Alkene Bonding<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/geometric-isomerism\/\">Geometric Isomerism<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/electrophilic-addition-mechanism\/\">Electrophilic Addition Mechanism<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/\">Reactions of Alkenes<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/halogens\/\">Halogens<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/hydrogen-halide\/\">Hydrogen Halide<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/bromine-water\/\">Bromine Water<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/hydrogen\/\">Hydrogen<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/steam\/\">Steam<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/kmno4\/\">KMnO4<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/polymerisation-reactions\/\">Polymerisation Reactions<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/polymer-waste\/\">Polymer Waste<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/halogenoalkanes\/\">Halogenoalkanes<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alcohols\/\">Alcohols<\/a>\r\n      <\/li>\r\n\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Next Topics<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/\">Topic 7 Modern Analytical Techniques I<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-5-formulae-equations-and-amounts-of-substance\/\">Topic 5 Formulae, Equations &amp; Amounts<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/\">Topic 4 Inorganic Chemistry &amp; The Periodic Table<\/a>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n<\/aside>\r\n\r\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      .replace(\/\\\/+$\/, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = sidebar.querySelectorAll('a[href]');\r\n    var matched = null;\r\n    var matchedLength = 0;\r\n\r\n    sidebar.querySelectorAll('.active, .active-main, .parent-active').forEach(function(item) {\r\n      item.classList.remove('active', 'active-main', 'parent-active');\r\n    });\r\n\r\n    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'-1');\r\n          matched.setAttribute('data-ols-disabled-parent', '1');\r\n        }\r\n      }\r\n    }\r\n\r\n    return true;\r\n  }\r\n\r\n  if (!highlightActive()) {\r\n    document.addEventListener('DOMContentLoaded', highlightActive);\r\n  }\r\n})();\r\n<\/script>\n\n  <main class=\"ols-main\">\n      <nav class=\"ols-breadcrumbs\" aria-label=\"Breadcrumb\">\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\">Revision Notes<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\">A Level Chemistry<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/\">Edexcel<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/\">Topic 6 Organic Chemistry I<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/\">Alkanes<\/a> \/\n        <span>Cracking<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Cracking<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to cracking larger hydrocarbons into smaller, more useful molecules, including alkanes, alkenes, the need for high temperature and the economic reasons for catalytic cracking.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Paper 2<\/div>\n          <div class=\"ols-badge\">Topic 6: Organic Chemistry I<\/div>\n          <div class=\"ols-badge\">9CH0\/02<\/div>\n        <\/div>\n      <\/header>\n<!-- 3D card: cracking-decane (22 Oct 2026) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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text-align:center; font-size:11px; font-style:italic; color:#aab0c0;\r\n}\r\n.ols-cc-crk-001 a{color:#aab0c0; text-decoration:none;}\r\n.ols-cc-crk-001 a:hover{text-decoration:underline;}\r\n.ols-crk-001 .crk-seg button{display:inline-flex; align-items:center;}\r\n.ols-crk-001 .crk-seg button .crk-n{display:inline-flex; align-items:center; justify-content:center; width:20px; height:20px; margin-right:9px; border-radius:50%; font-size:11px; font-weight:600; background:rgba(37,99,235,0.10); color:#2563eb; flex:0 0 auto;}\r\n.ols-crk-001 .crk-seg button[aria-pressed=\"true\"] .crk-n{background:#ffffff; color:#2563eb;}\r\n<\/style>\r\n\r\n<div class=\"crk-head\">\r\n  <h2 class=\"crk-title\">Cracking: Breaking a Long Alkane<\/h2>\r\n  <p class=\"crk-sub\">Choose a step to watch decane break into a shorter alkane and an alkene: heat, a C\u2013C bond breaking, a hydrogen atom moving, and the zeolite catalyst.<\/p>\r\n<\/div>\r\n\r\n<div class=\"crk-stage\" id=\"crkStage\">\r\n  <canvas class=\"crk-canvas\" id=\"crkCanvas\"><\/canvas>\r\n  <div class=\"crk-overlay\" id=\"crkOverlay\"><\/div>\r\n  <div class=\"crk-caption\" id=\"crkCaption\"><\/div>\r\n  <div class=\"crk-hint\" id=\"crkHint\">Drag to rotate<\/div>\r\n  <div class=\"crk-badges\" id=\"crkBadges\"><\/div>\r\n<\/div>\r\n\r\n<div class=\"crk-controls\">\r\n  <div class=\"crk-row\">\r\n    <span class=\"crk-rowlab\">Step<\/span>\r\n    <div class=\"crk-seg\" role=\"group\" aria-label=\"Step\">\r\n      <button type=\"button\" data-step=\"1\" aria-pressed=\"true\"><span class=\"crk-n\">1<\/span>Heat decane<\/button>\r\n      <button type=\"button\" data-step=\"2\" aria-pressed=\"false\"><span class=\"crk-n\">2<\/span>A C\u2013C bond breaks<\/button>\r\n      <button type=\"button\" data-step=\"3\" aria-pressed=\"false\"><span class=\"crk-n\">3<\/span>Alkane + alkene<\/button>\r\n      <button type=\"button\" data-step=\"4\" aria-pressed=\"false\"><span class=\"crk-n\">4<\/span>Catalytic cracking<\/button>\r\n    <\/div>\r\n  <\/div>\r\n\r\n  <div class=\"crk-row\">\r\n    <span class=\"crk-rowlab\">View<\/span>\r\n    <button type=\"button\" class=\"crk-pill\" id=\"crkResetV\">Reset view<\/button>\r\n  <\/div>\r\n<\/div>\r\n\r\n<div class=\"crk-info\">\r\n  <h3 id=\"crkInfoTitle\"><\/h3>\r\n  <p id=\"crkInfoText\"><\/p>\r\n  <div class=\"crk-facts\" id=\"crkFacts\"><\/div>\r\n  <div class=\"crk-key\">\r\n    <span><i class=\"k-ball\" style=\"background:#464a54\"><\/i>Carbon<\/span>\r\n    <span><i class=\"k-ball\" style=\"background:#ececf0\"><\/i>Hydrogen<\/span>\r\n    <span><i class=\"k-ball\" style=\"background:#f6c426\"><\/i>Unpaired electron<\/span>\r\n    <span><i class=\"k-ball\" style=\"background:#969ca8\"><\/i>Silicon (zeolite)<\/span>\r\n    <span><i class=\"k-ball\" style=\"background:#cc463c\"><\/i>Oxygen (zeolite)<\/span>\r\n  <\/div>\r\n<\/div>\r\n\r\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/cracking-decane.js?v=20261025p\"><\/script>\r\n<\/section>\r\n\r\n<p class=\"ols-cc-crk-001\">&copy; Dr. Mohammed Al-Fatah &#8211; <a href=\"https:\/\/www.onlinelearningsystem.net\" target=\"_blank\" rel=\"noopener\">onlinelearningsystem.net<\/a><\/p>\n\n\n      \n<section class=\"ols-h5p-card ols-h5p-inline ols-h5p-recap\">\n<span class=\"ols-h5p-kicker\">Before you start<\/span>\n<h2>GCSE Recap: Alkenes, Bromine Water and Bond Breaking<\/h2>\n<p>Start with the GCSE ideas about alkenes and bond breaking that cracking relies on.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"695\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">1<\/div>\n          <h2>What Is Cracking?<\/h2>\n        <\/div>\n\n        <p><strong>Cracking<\/strong> is a chemical process in which <strong>large hydrocarbon molecules<\/strong> are broken down into <strong>smaller, more useful molecules<\/strong>.<\/p>\n        <p>This happens by the <strong>breaking of carbon-carbon covalent bonds<\/strong>, written as <strong>C-C bonds<\/strong>, within the larger hydrocarbon molecule.<\/p>\n        <p>Cracking is used because smaller hydrocarbons are often in <strong>greater demand<\/strong>, especially as fuels and as feedstocks for making plastics and other chemicals.<\/p>\n\n        <div class=\"ols-definition-box\">\n          <div class=\"ols-definition-circle\">Crack<\/div>\n          <p><strong>Cracking:<\/strong> the breaking down of long-chain hydrocarbons into shorter-chain hydrocarbons by breaking C-C bonds.<\/p>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> Unlike fractional distillation, cracking is a chemical process because covalent bonds are broken and new molecules are formed.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">2<\/div>\n          <h2>Products of Cracking<\/h2>\n        <\/div>\n\n        <p>During cracking, high relative molecular mass, <strong>M<sub>r<\/sub><\/strong>, alkanes are converted into a mixture of <strong>smaller alkanes<\/strong> and <strong>alkenes<\/strong>. Hydrogen gas may also be produced.<\/p>\n        <p>An alkane cannot crack into smaller alkanes only. There are not enough hydrogen atoms to go round, so at least one product must be an <strong>alkene<\/strong>, or hydrogen itself. Check any set of products by counting the atoms on each side.<\/p>\n        <p>For example, decane can be cracked into octane and ethene:<\/p>\n\n        <div class=\"ols-definition-box\">\n          <p style=\"text-align: center; font-size: clamp(24px, 4vw, 42px); line-height: 1.35; font-weight: 800; color: #111827;\"><strong>C<sub>10<\/sub>H<sub>22<\/sub> &rarr; C<sub>8<\/sub>H<sub>18<\/sub> + C<sub>2<\/sub>H<sub>4<\/sub><\/strong><\/p>\n        <\/div>\n\n        <p>In this example, <strong>C<sub>10<\/sub>H<sub>22<\/sub><\/strong> is a larger alkane, <strong>C<sub>8<\/sub>H<sub>18<\/sub><\/strong> is a smaller alkane and <strong>C<sub>2<\/sub>H<sub>4<\/sub><\/strong> is an alkene.<\/p>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <a class=\"ols-cracking-image-link\" href=\"#ols-cracking-lightbox\" aria-label=\"Open cracking diagram fullscreen\">\n              <img decoding=\"async\" class=\"ols-safe-hover-img ols-zoomable-img ols-cracking-zoom-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-cd-03-crackingdecane.svg\" alt=\"Displayed formulae: decane cracking into octane and ethene, with the C\u2013C bond that breaks marked\" width=\"1520\" height=\"1144\">\n            <\/a>\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>A long-chain hydrocarbon is converted into smaller, more useful molecules by breaking C-C bonds.<\/p>\n          <\/div>\n        <\/div>\n\n        <a id=\"ols-cracking-lightbox\" class=\"ols-lightbox-overlay\" href=\"#\" role=\"dialog\" aria-modal=\"true\" aria-label=\"Image lightbox\">\n          <span class=\"ols-lightbox-close\" aria-label=\"Close lightbox\">&times;<\/span>\n          <img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/skel-85-cracking-displayed.svg\" alt=\"Cracking of decane to octane and ethene shown as displayed formulae\">\n        <\/a>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Product type<\/th>\n                <th>Example from the equation<\/th>\n                <th>Why it matters<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Product type\"><strong>Smaller alkane<\/strong><\/td>\n                <td data-label=\"Example from the equation\">C<sub>8<\/sub>H<sub>18<\/sub>, octane.<\/td>\n                <td data-label=\"Why it matters\">Smaller alkanes are useful as motor fuels.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Product type\"><strong>Alkene<\/strong><\/td>\n                <td data-label=\"Example from the equation\">C<sub>2<\/sub>H<sub>4<\/sub>, ethene.<\/td>\n                <td data-label=\"Why it matters\">Alkenes are useful feedstocks for making polymers and other chemicals.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Product type\"><strong>Hydrogen gas<\/strong><\/td>\n                <td data-label=\"Example from the equation\">H<sub>2<\/sub> may be produced in some cracking reactions.<\/td>\n                <td data-label=\"Why it matters\">Hydrogen can be formed alongside smaller hydrocarbons, depending on the reaction pathway.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Find the Missing Product<\/h2>\n<p>Count the atoms to find the missing product in each cracking equation.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-106\" class=\"h5p-iframe\" data-content-id=\"106\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Cracking Flashcards: Find the Missing Product\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">3<\/div>\n          <h2>Why Cracking Needs High Temperature<\/h2>\n        <\/div>\n\n        <p>Cracking involves the <strong>breaking of strong covalent bonds<\/strong>. This means the reaction requires a large amount of energy.<\/p>\n        <p>High temperatures are used to provide enough energy for the C-C bonds in larger hydrocarbons to break.<\/p>\n        <p>There are two routes. <strong>Thermal cracking<\/strong> uses a very high temperature and a high pressure (about 1200 K and 7000 kPa) and gives a high proportion of <strong>alkenes<\/strong>.<\/p>\n<p><strong>Catalytic cracking<\/strong> passes the vapour over a <strong>zeolite<\/strong> catalyst at a lower temperature and only a slight pressure (about 720 K), and gives mainly branched and aromatic molecules for motor fuels.<\/p>\n        <p>The catalyst provides a route of <strong>lower activation energy<\/strong>, so the same rate is reached at a lower temperature. That is what saves energy and money, not a vague improvement in efficiency.<\/p>\n\n        <div class=\"ols-warning-box\">\n          <p><strong>Important:<\/strong> Do not describe cracking as a physical separation. Cracking changes the molecules present, so it is a chemical reaction.<\/p>\n        <\/div>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Process<\/th>\n                <th>What happens to bonds?<\/th>\n                <th>Type of change<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Process\"><strong>Fractional distillation<\/strong><\/td>\n                <td data-label=\"What happens to bonds?\">Weak London forces between molecules are overcome.<\/td>\n                <td data-label=\"Type of change\">Physical separation.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Process\"><strong>Cracking<\/strong><\/td>\n                <td data-label=\"What happens to bonds?\">Strong C-C covalent bonds within molecules are broken.<\/td>\n                <td data-label=\"Type of change\">Chemical reaction.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Bonds, Energy and Evidence<\/h2>\n<p>Choose the accurate statement about bonds, energy and evidence of reaction in each round.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-105\" class=\"h5p-iframe\" data-content-id=\"105\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Cracking Summary: Bonds, Energy and Evidence of Reaction\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card green\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Economic Reasons for Catalytic Cracking<\/h2>\n        <\/div>\n\n        <p>Catalytic cracking is economically important because it converts less useful long-chain hydrocarbons into shorter molecules that are in greater demand.<\/p>\n\n        <ul>\n          <li>Petroleum fractions that contain <strong>shorter carbon chains<\/strong>, such as petrol and naphtha, are in <strong>greater demand<\/strong> than fractions made from longer hydrocarbon molecules.<\/li>\n          <li>Longer hydrocarbons are often produced in excess, so they are <strong>cracked<\/strong> to increase the supply of shorter, more useful molecules.<\/li>\n          <li>The products formed during cracking are generally <strong>more valuable and commercially useful<\/strong> than the original hydrocarbons.<\/li>\n          <li><strong>Ethene<\/strong> is an important raw material used to manufacture <strong>poly(ethene)<\/strong>, <strong>ethane-1,2-diol<\/strong> and <strong>ethanol<\/strong>.<\/li>\n          <li>Smaller alkanes are widely used as <strong>motor fuels<\/strong> because they are more <strong>volatile<\/strong> and ignite more easily, which is what a petrol engine needs, and because they meet consumer demand more effectively.<\/li>\n        <\/ul>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> Link cracking to demand and supply. Longer hydrocarbons are less useful and often in excess, while shorter alkanes and alkenes are more commercially valuable.<\/p>\n        <\/div>\n      <div class=\"ols-figure-card ols-zoom-pop\">\n<div class=\"ols-figure-image\">\n<a class=\"ols-image-fullscreen-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-52-crackdemand.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-52-crackdemand.jpg\" alt=\"Bar chart of supply against demand for five crude oil fractions, with thermal and catalytic cracking conditions\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-52-crackdemand.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Heavy fractions are in surplus and petrol-range fractions in short supply, so cracking turns one into the other.<\/p><\/div>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Explain Why the Refinery Cracks Fuel Oil<\/h2>\n<p>Use the refinery data to explain why part of the fuel oil is cracked.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-696\" class=\"h5p-iframe\" data-content-id=\"696\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Cracking Explain: Why a Refinery Cracks Its Fuel Oil\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card yellow\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>Cracking and Alkene Feedstocks<\/h2>\n        <\/div>\n\n        <p>One of the most important outcomes of cracking is the production of <strong>alkenes<\/strong>. These molecules contain a <strong>C=C double bond<\/strong>, making them more reactive than alkanes.<\/p>\n        <p>Alkenes are useful because they can be converted into many products, including polymers and alcohols. Ethene is a key example because it is used to make poly(ethene), ethane-1,2-diol and ethanol.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Cracking product<\/th>\n                <th>Commercial use<\/th>\n                <th>Reason it is useful<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Cracking product\"><strong>Shorter alkanes<\/strong><\/td>\n                <td data-label=\"Commercial use\">Motor fuels.<\/td>\n                <td data-label=\"Reason it is useful\">They are in greater demand, and they are more volatile, so they ignite more easily in an engine.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Cracking product\"><strong>Alkenes<\/strong><\/td>\n                <td data-label=\"Commercial use\">Chemical feedstocks.<\/td>\n                <td data-label=\"Reason it is useful\">They can be used to make polymers and other industrial chemicals.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Cracking product\"><strong>Ethene<\/strong><\/td>\n                <td data-label=\"Commercial use\">Poly(ethene), ethane-1,2-diol and ethanol manufacture.<\/td>\n                <td data-label=\"Reason it is useful\">It is a reactive alkene and an important raw material.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n      <div class=\"ols-figure-card ols-zoom-pop\">\n<div class=\"ols-figure-image\">\n<a class=\"ols-image-fullscreen-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-53-crackevidence.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-53-crackevidence.jpg\" alt=\"Cracking decane into octane and ethene, the atom check, the bromine water test and uses of the alkene\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-53-crackevidence.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Cracking breaks C\u2013C bonds to give a shorter alkane and an alkene, and the alkene decolourises bromine water.<\/p><\/div>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Pick Out the Alkene Feedstocks<\/h2>\n<p>Click every product that is an alkene and could be sold as a feedstock.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-104\" class=\"h5p-iframe\" data-content-id=\"104\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Cracking Mark the Words: Alkene Feedstocks in the Product Stream\"><\/iframe><\/div><\/div>\n<\/section>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Cracking Round-Up<\/h2>\n<p>Finish by applying the whole page to four new questions.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1283\"><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">6<\/div>\n          <h2>Common Exam Mistakes<\/h2>\n        <\/div>\n\n        <ul>\n          <li>Do not say cracking is a physical process. It is a <strong>chemical process<\/strong>.<\/li>\n          <li>Do not say only alkanes are produced. Cracking can produce <strong>smaller alkanes and alkenes<\/strong>.<\/li>\n          <li>Do not forget that <strong>hydrogen gas<\/strong> may also be produced.<\/li>\n          <li>Do not confuse cracking with fractional distillation. Fractional distillation separates fractions, while cracking changes molecules.<\/li>\n          <li>Do not describe cracking only as a way to make fuels. It also produces <strong>alkenes for chemical synthesis<\/strong>.<\/li>\n        <\/ul>\n      <\/article>\n\n      \n\n      <section class=\"ols-faq-card\" id=\"cracking-faq\">\n        <h2>Cracking FAQ<\/h2>\n        <p>Quick answers to common cracking questions for Edexcel A Level Chemistry.<\/p>\n\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>What is cracking in organic chemistry?<\/h3>\n            <p>Cracking is a chemical process where large hydrocarbon molecules are broken into smaller, more useful molecules by breaking carbon-carbon covalent bonds.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What products are formed during cracking?<\/h3>\n            <p>Cracking usually forms a mixture of smaller alkanes and alkenes. Hydrogen gas may also be produced depending on the reaction.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why does cracking need a high temperature?<\/h3>\n            <p>Cracking needs a high temperature because strong covalent C-C bonds must be broken, so enough energy is required for the reaction to occur.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why is catalytic cracking economically useful?<\/h3>\n            <p>Catalytic cracking converts longer hydrocarbons that may be in excess into shorter alkanes and alkenes that are in greater demand and have higher commercial value.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why must cracking always give an alkene or hydrogen?<\/h3>\n            <p>An alkane already holds the most hydrogen its chain can carry. Splitting it into two smaller molecules leaves too few hydrogen atoms for both to be alkanes, so one product is an alkene or hydrogen forms.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <!-- author card (moved to the end, 10 Oct 2026) -->\n      <div class=\"ols-author\">\n        \n            <img decoding=\"async\"\n              class=\"ols-author-avatar-img\"\n              src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\"\n              alt=\"Dr. Mohammed Al-Fatah\"\n            >\n        \n            <div class=\"ols-author-content\">\n        \n              <h2 class=\"ols-author-title\">\n                Written by: Dr. Mohammed Al-Fatah\n              <\/h2>\n        \n              <p class=\"ols-author-description\">\n                Chemistry specialist revision notes for A Level Chemistry.\n              <\/p>\n        \n              <a\n                class=\"ols-linkedin-pill\"\n                href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\"\n                target=\"_blank\"\n                rel=\"noopener noreferrer\"\n              >\n        \n                <svg class=\"ols-linkedin-icon\" viewBox=\"0 0 24 24\" fill=\"currentColor\" aria-hidden=\"true\">\n                  <path d=\"M4.98 3.5C4.98 4.88 3.86 6 2.48 6S0 4.88 0 3.5 1.12 1 2.48 1s2.5 1.12 2.5 2.5zM.5 8h4V24h-4V8zm7 0h3.8v2.2h.1c.5-.9 1.8-2.2 3.9-2.2 4.2 0 5 2.8 5 6.4V24h-4v-7.6c0-1.8 0-4.2-2.6-4.2s-3 2-3 4v7.8h-4V8z\"\/>\n                <\/svg>\n        \n                View LinkedIn Profile\n        \n              <\/a>\n        \n            <\/div>\n        \n          <\/div>\n\n\n<section class=\"ols-related-card\">\n        <h2>Related Topic 6 Organic Chemistry I Revision Notes<\/h2>\n        <p>Continue building the Topic 6 Organic Chemistry I sequence with the next connected pages.<\/p>\n\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/fractional-distillation\/\">Fractional Distillation<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/reforming\/\">Reforming<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/combustion\/\">Alkanes as Fuel<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/free-radical-substitution\/\">Reactions of Alkanes<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/\">Introduction to Organic Chemistry<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/isomerism\/\">Isomerism<\/a>\n        <\/div>\n      <\/section>\n\n      <!-- OLS Author Copyright Footprint \/ Attribution Card -->\n      <section class=\"ols-attribution-card ols-attr-std\" aria-label=\"Copyright notice\">\n<style id=\"ols-attribution-card-css\">.ols-attribution-card.ols-attr-std{background:linear-gradient(135deg,#ffffff,#f8fbff);border:1px solid rgba(28,36,75,0.14);border-radius:28px;box-shadow:0 18px 45px rgba(28,36,75,0.10);padding:34px;margin:24px 0;overflow:hidden;font-family:Poppins,Arial,sans-serif;box-sizing:border-box}.ols-attribution-card.ols-attr-std *{box-sizing:border-box}.ols-attribution-card.ols-attr-std p{margin:0;font-size:14px;line-height:1.65;font-weight:300;color:#667085}.ols-attribution-card.ols-attr-std strong{font-weight:700;color:#1C244B}@media (max-width:760px){.ols-attribution-card.ols-attr-std{padding:24px 18px;border-radius:22px}}<\/style>\n<p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n<\/section>\n    <\/main>\n\n<script>\n(function(){\n  var page = document.querySelector('.ols-cracking-page');\n  if (!page) return;\n\n  var images = page.querySelectorAll('.ols-safe-hover-img');\n  if (!images.length) return;\n\n  function applySafeHoverZoom(img) {\n    if (window.matchMedia && window.matchMedia('(max-width: 760px)').matches) {\n      return;\n    }\n\n    var rect = img.getBoundingClientRect();\n\n    if (!rect.width || !rect.height) {\n      return;\n    }\n\n    var viewportW = window.innerWidth || document.documentElement.clientWidth;\n    var viewportH = window.innerHeight || document.documentElement.clientHeight;\n\n    \/*\n      3% viewport safety margin.\n      The zoomed image is kept approximately 3vw from left\/right\n      and 3vh from top\/bottom.\n    *\/\n    var marginX = viewportW * 0.03;\n    var marginY = viewportH * 0.03;\n\n    var availableW = viewportW - (marginX * 2);\n    var availableH = viewportH - (marginY * 2);\n\n    var scaleLimitW = availableW \/ rect.width;\n    var scaleLimitH = availableH \/ rect.height;\n\n    \/*\n      Preferred maximum zoom is 150%.\n      Large images automatically receive a smaller safe scale.\n    *\/\n    var targetScale = 1.5;\n    var safeScale = Math.min(targetScale, scaleLimitW, scaleLimitH);\n\n    \/*\n      Do not shrink an image on hover. 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