{"id":7453,"date":"2026-09-10T21:08:51","date_gmt":"2026-09-10T20:08:51","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/crude-oil\/thermal-and-catalytic-cracking\/"},"modified":"2026-09-22T12:20:38","modified_gmt":"2026-09-22T11:20:38","slug":"thermal-and-catalytic-cracking","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/crude-oil\/thermal-and-catalytic-cracking\/","title":{"rendered":"Thermal and Catalytic 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: 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16px; padding: 26px 22px; font-weight: 700; color: #7a4b12; text-align: center; line-height: 1.6; }\n    .ols-figure-placeholder .ols-figure-image { background: transparent; }\n    .ols-figure-placeholder { background: #ffffff; border: 1px solid rgba(28, 36, 75, 0.12); border-radius: 22px; padding: 14px; margin: 18px 0 6px; }\n    .ols-figure-placeholder .ols-figure-caption p { margin: 10px 0 0; font-size: 14px; color: #667085; text-align: center; }\n<\/style>\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>AQA A Level Chemistry<\/p>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>3.3.2 Alkanes<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/\">Section overview<\/a><\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/crude-oil\/\">Alkanes from Crude Oil<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/crude-oil\/fractional-distillation\/\">Fractional Distillation<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/crude-oil\/cracking\/\">Cracking<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/crude-oil\/reforming\/\">Reforming<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/crude-oil\/thermal-and-catalytic-cracking\/\">Thermal and Catalytic Cracking<\/a><\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/fuel\/\">Alkanes as Fuel<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/fuel\/combustion\/\">Combustion<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/fuel\/oxides-of-sulfur\/\">Oxides of Sulfur<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/fuel\/oxides-of-nitrogen\/\">Oxides of Nitrogen<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/fuel\/catalytic-converter\/\">Catalytic Converter<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/fuel\/flue-gas-desulfurisation\/\">Flue-Gas Desulfurisation<\/a><\/li>\n        <\/ul>\n      <\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/alternative-fuel\/\">Alternative Fuel<\/a><\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/reactions\/\">Reactions of Alkanes<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/reactions\/free-radical-substitution\/\">Free Radical Substitution<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/reactions\/initiation\/\">Initiation<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/reactions\/propagation\/\">Propagation<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/reactions\/termination\/\">Termination<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/reactions\/further-substitution\/\">Further Substitution<\/a><\/li>\n        <\/ul>\n      <\/li>\n    <\/ul>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>Other AQA Sections<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-1-introduction-to-organic-chemistry\/\">3.3.1 Introduction to Organic Chemistry<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-4-alkenes\/\">3.3.4 Alkenes<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-1-atomicstructure\/\">3.1.1 Atomic Structure<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/\">3.1.2 Amount of Substance<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/\">3.1.3 Bonding<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-1-periodicity\/\">3.2.1 Periodicity<\/a><\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\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      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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\/aqa\/\">AQA<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/\">3.3.2 Alkanes<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/crude-oil\/\">Alkanes from Crude Oil<\/a> \/\n<span>Thermal and Catalytic Cracking<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Thermal and Catalytic Cracking<\/h1>\n        <p class=\"ols-page-intro\">A concise AQA A Level Chemistry revision guide to the two types of cracking named in 3.3.2.2: the conditions and products of thermal cracking, the zeolite catalyst and products of catalytic cracking, and the economic reasons why cracking is carried out.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Paper 2<\/div>\n<div class=\"ols-badge\">AQA<\/div>\n<div class=\"ols-badge\">3.3.2 Alkanes<\/div>\n<div class=\"ols-badge\">7405\/2<\/div>\n        <\/div>\n\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 class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\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      <\/header>\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: From Crude Oil to Shorter Molecules<\/h2>\n<p>Before you start, check what distillation gives a refinery and what cracking does to a chain.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"813\"><\/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>Why AQA Names Two Types of Cracking<\/h2>\n<\/div>\n<p>Cracking breaks <strong>C-C bonds<\/strong> in the long-chain alkanes from crude oil to give shorter, more useful molecules. AQA 3.3.2.2 goes further than most specifications: it names <strong>thermal cracking<\/strong> and <strong>catalytic cracking<\/strong> separately, states the conditions for each, and asks for the products each is used to make. The general cracking page covers the idea; this page covers the AQA detail.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th><\/th><th>Thermal cracking<\/th><th>Catalytic cracking<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Temperature<\/strong><\/td><td>High, around 700 to 1200 K<\/td><td>High, around 720 K<\/td><\/tr>\n<tr><td><strong>Pressure<\/strong><\/td><td>High, up to about 7000 kPa<\/td><td>Slight, a little above atmospheric<\/td><\/tr>\n<tr><td><strong>Catalyst<\/strong><\/td><td>None<\/td><td>Zeolite<\/td><\/tr>\n<tr><td><strong>How the C-C bond breaks<\/strong><\/td><td>Homolytic fission, giving radicals (mechanism not required)<\/td><td>Via carbocation intermediates on the catalyst surface (mechanism not required)<\/td><\/tr>\n<tr><td><strong>Main products<\/strong><\/td><td>A high percentage of alkenes, plus some shorter alkanes<\/td><td>Branched alkanes, cycloalkanes and aromatic hydrocarbons<\/td><\/tr>\n<tr><td><strong>Used mainly to make<\/strong><\/td><td>Alkenes for polymers and other chemicals<\/td><td>Motor fuels and aromatic hydrocarbons<\/td><\/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\/09\/side-by-side-infographic-comparing-thermal-and-catalytic-cracking.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/side-by-side-infographic-comparing-thermal-and-catalytic-cracking.jpg\" alt=\"Comparison of thermal cracking and catalytic cracking conditions, catalyst and products\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/side-by-side-infographic-comparing-thermal-and-catalytic-cracking.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>The AQA comparison: thermal cracking uses high temperature and high pressure to make alkenes; catalytic cracking uses a zeolite catalyst at slight pressure to make motor fuels and aromatics.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Learn the table as pairs: thermal = high pressure + high temperature + alkenes; catalytic = slight pressure + high temperature + zeolite + motor fuels and aromatics.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">2<\/div>\n<h2>Thermal Cracking<\/h2>\n<\/div>\n<p>In thermal cracking the alkane vapour is heated to a <strong>high temperature<\/strong> under <strong>high pressure<\/strong> for a very short time. The energy breaks C-C bonds <strong>homolytically<\/strong>, forming free radicals which then rearrange into the products. Because hydrogen atoms are lost as the chains break, the products contain a <strong>high percentage of alkenes<\/strong>.<\/p>\n<p>A long alkane can crack in many ways, so a mixture forms. Every equation must balance, and one product is always an alkene:<\/p>\n<ul>\n<li>C<sub>14<\/sub>H<sub>30<\/sub> &rarr; C<sub>8<\/sub>H<sub>18<\/sub> + C<sub>6<\/sub>H<sub>12<\/sub> (octane and hexene)<\/li>\n<li>C<sub>14<\/sub>H<sub>30<\/sub> &rarr; C<sub>10<\/sub>H<sub>22<\/sub> + 2C<sub>2<\/sub>H<sub>4<\/sub> (decane and two molecules of ethene)<\/li>\n<li>C<sub>14<\/sub>H<sub>30<\/sub> &rarr; C<sub>14<\/sub>H<sub>28<\/sub> + H<sub>2<\/sub> (an alkene and hydrogen, when only a C-H bond breaks)<\/li>\n<\/ul>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Thermal cracking takes place at high temperature and high pressure and produces a high percentage of alkenes, which are the starting materials for addition polymers.<\/p>\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: Balance the Cracking Equations<\/h2>\n<p>Work out the missing formula or number in each equation on paper, then type it in.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-386\" class=\"h5p-iframe\" data-content-id=\"386\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Thermal and Catalytic Cracking Blanks: Balancing Five Thermal Cracking Equations\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card purple\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">3<\/div>\n<h2>Catalytic Cracking<\/h2>\n<\/div>\n<p>Catalytic cracking uses a <strong>zeolite<\/strong> catalyst at a <strong>high temperature<\/strong> and a <strong>slight pressure<\/strong>, only a little above atmospheric. Zeolites are aluminosilicates with a honeycomb structure of pores, which gives a very large surface area and lets the catalyst select molecules by size. The catalyst allows the reaction to run at a lower temperature and pressure than thermal cracking, which cuts the energy cost.<\/p>\n<p>The products are different because the reaction goes through <strong>carbocation<\/strong> intermediates rather than radicals. Carbocations rearrange to the more stable branched forms, so catalytic cracking gives mainly:<\/p>\n<ul>\n<li><strong>Branched alkanes<\/strong>, such as 2,2,4-trimethylpentane, which burn smoothly in petrol engines (high octane number);<\/li>\n<li><strong>Cycloalkanes<\/strong>;<\/li>\n<li><strong>Aromatic hydrocarbons<\/strong>, such as benzene and methylbenzene, used as fuel components and as chemical feedstocks.<\/li>\n<\/ul>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Feature of the zeolite catalyst<\/th><th>Why it matters<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Honeycomb structure with many pores<\/strong><\/td><td>Very large surface area, so the reaction is fast<\/td><\/tr>\n<tr><td><strong>Acidic sites on the surface<\/strong><\/td><td>Generate the carbocations that rearrange to branched products<\/td><\/tr>\n<tr><td><strong>Pores of a fixed size<\/strong><\/td><td>Only molecules that fit can react, which controls the product mix<\/td><\/tr>\n<tr><td><strong>Solid catalyst<\/strong><\/td><td>Easily separated from the gaseous products and regenerated<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Catalytic cracking takes place at a slight pressure, high temperature and in the presence of a zeolite catalyst, and is used mainly to produce motor fuels and aromatic hydrocarbons.<\/p>\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: Pore Size in a Zeolite<\/h2>\n<p>Use what the pores do to predict how this catalyst would handle a heavy feedstock.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-385\" class=\"h5p-iframe\" data-content-id=\"385\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Thermal and Catalytic Cracking MCQ: What the Size of the Zeolite Pores Does\"><\/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: Explain the Two Octane Numbers<\/h2>\n<p>Write a short explanation, then compare it with the mark points and the model answer.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-814\" class=\"h5p-iframe\" data-content-id=\"814\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Thermal and Catalytic Cracking Explain: Why the Catalytic Petrol Has the Higher Octane Number\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>The Economic Reasons for Cracking<\/h2>\n<\/div>\n<p>Fractional distillation gives the fractions in the proportions found in crude oil, but demand does not match supply. The <strong>short-chain fractions<\/strong> (petrol, and gases such as ethene) are in <strong>high demand<\/strong> and command high prices, while the <strong>long-chain fractions<\/strong> (heavy fuel oil, bitumen) are in <strong>surplus<\/strong> and sell cheaply. Cracking converts the cheap surplus into the valuable products.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Economic reason<\/th><th>Explanation<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Matches supply to demand<\/strong><\/td><td>Long-chain fractions that would otherwise be surplus are turned into the petrol and gases that customers want<\/td><\/tr>\n<tr><td><strong>Makes more valuable products<\/strong><\/td><td>Petrol and alkenes sell for far more per tonne than heavy fuel oil<\/td><\/tr>\n<tr><td><strong>Provides alkenes as feedstock<\/strong><\/td><td>Ethene and propene from thermal cracking are the monomers for poly(ethene) and poly(propene) and the starting point for many other chemicals<\/td><\/tr>\n<tr><td><strong>Improves fuel quality<\/strong><\/td><td>Branched and aromatic products from catalytic cracking give petrol with a higher octane number<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> An &#8220;explain the economic reasons&#8221; question needs both halves: the long-chain fractions are in low demand and low value, and the short-chain products are in high demand and high value.<\/p>\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: Which Cracker?<\/h2>\n<p>Decide which process each refinery observation points to, or whether it fits both.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-384\" class=\"h5p-iframe\" data-content-id=\"384\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Thermal and Catalytic Cracking Quick Fire: Which Cracker Is Being Described?\"><\/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: Judge the Claims<\/h2>\n<p>In each round, choose the one statement that is accurate.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-387\" class=\"h5p-iframe\" data-content-id=\"387\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Thermal and Catalytic Cracking Summary: Four Claims About Why Refineries Crack\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card purple\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Common Exam Mistakes<\/h2>\n<\/div>\n<ul>\n<li>Swapping the pressures: thermal cracking is <strong>high<\/strong> pressure, catalytic cracking is <strong>slight<\/strong> pressure.<\/li>\n<li>Saying that catalytic cracking produces mainly alkenes. Alkenes are the main product of <strong>thermal<\/strong> cracking; catalytic cracking gives motor fuels and aromatics.<\/li>\n<li>Naming the catalyst as &#8220;a metal&#8221; or &#8220;platinum&#8221;. AQA expects <strong>zeolite<\/strong>.<\/li>\n<li>Writing a cracking equation that does not balance, or one with no alkene among the products.<\/li>\n<li>Answering an economics question with chemistry only. Mention demand, surplus and value.<\/li>\n<\/ul>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Cracking is carried out because the long-chain fractions from distillation are in low demand, while the shorter alkanes and alkenes produced are in high demand and are more valuable.<\/p>\n<\/div>\n<\/article>\n\n<section class=\"ols-course-cta-alkenes\" id=\"olsCourseCtaAlkenes001\">\r\n  <style>\r\n    .ols-course-cta-alkenes,\r\n    .ols-course-cta-alkenes * {\r\n      box-sizing: border-box;\r\n    }\r\n\r\n    .ols-course-cta-alkenes {\r\n      --navy: #1C244B;\r\n      --blue: #2563eb;\r\n      --body-text: #1f2937;\r\n      --grey-text: #667085;\r\n      --border: rgba(28, 36, 75, 0.14);\r\n      --shadow: 0 18px 45px rgba(28, 36, 75, 0.12);\r\n      --inner-shadow: 0 10px 26px rgba(28, 36, 75, 0.08);\r\n\r\n      width: 100%;\r\n      margin: 30px 0 24px;\r\n      font-family: Poppins, Arial, sans-serif;\r\n    }\r\n\r\n    .ols-course-cta-alkenes 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class=\"ols-course-cta-image-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/introduction-to-organic-chemistry-and-alkanes-3-3-1-3-3-2-aqa\/\" aria-label=\"Open the AQA A Level Chemistry 3.3.1 and 3.3.2 Introduction to Organic Chemistry and Alkanes course page\">\r\n\r\n        <div class=\"ols-course-cta-image\">\r\n          <img decoding=\"async\"\r\n            src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/aqa-a-level-chemistry-3-3-1-3-3-2-organic-chemistry-alkanes-interactive-course-banner.jpg\"\r\n            alt=\"AQA A Level Chemistry 3.3.4 Introduction to Organic Chemistry and Alkanes interactive course banner\"\r\n          >\r\n        <\/div>\r\n\r\n      <\/a>\r\n\r\n      <div class=\"ols-course-cta-content\">\r\n\r\n        <div class=\"ols-course-cta-header-row\">\r\n\r\n          <div class=\"ols-course-cta-kicker\">\r\n            AQA 7405 | 3.3.1 and 3.3.2 Course\r\n          <\/div>\r\n\r\n          <a class=\"ols-course-button ols-course-button-top\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/introduction-to-organic-chemistry-and-alkanes-3-3-1-3-3-2-aqa\/\">\r\n            View Course\r\n          <\/a>\r\n\r\n        <\/div>\r\n\r\n        <h2>\r\n          Master Introduction to Organic Chemistry and Alkanes for AQA A Level Chemistry\r\n        <\/h2>\r\n\r\n      <\/div>\r\n\r\n    <\/div>\r\n\r\n    <div class=\"ols-course-cta-intro-stats\">\r\n\r\n      <p class=\"ols-course-cta-intro\">\r\n        Continue from these free revision notes into the full 3.3.1 and 3.3.2 Introduction to Organic Chemistry and Alkanes course. The six guided video lessons are ready now; the AQA MCQ bank, teacher-marked short-answer questions, supplementary lessons and KASP spec-point report are being written, and the course opens for enrolment as soon as they are complete.\r\n      <\/p>\r\n\r\n      <div class=\"ols-course-cta-stats\">\r\n\r\n        <div class=\"ols-course-stat\">\r\n          <span>Recorded lessons<\/span>\n          <strong>Coming soon<\/strong>\r\n        <\/div>\r\n\r\n        <div class=\"ols-course-stat\">\r\n          <span>Video lessons<\/span>\n          <strong>Coming soon<\/strong>\r\n        <\/div>\r\n\r\n        <div class=\"ols-course-stat\">\r\n          <span>MCQ practice<\/span>\n          <strong>Coming soon<\/strong>\r\n        <\/div>\r\n\r\n        <div class=\"ols-course-stat\">\r\n          <span>SAQ practice<\/span>\n          <strong>Coming soon<\/strong>\r\n        <\/div>\r\n\r\n      <\/div>\r\n\r\n    <\/div>\r\n\r\n    <div class=\"ols-course-cta-features\">\r\n\r\n      <div class=\"ols-course-feature\">\r\n        <h3>Guided video teaching<\/h3>\r\n        <p>\r\n          Learn the chemistry and exam technique through structured video lessons with worked examples and walkthroughs.\r\n        <\/p>\r\n      <\/div>\r\n\r\n      <div class=\"ols-course-feature\">\r\n        <h3>Instant MCQ feedback<\/h3>\r\n        <p>\r\n          Auto-marked MCQ quizzes provide immediate diagnostic feedback for every answer choice.\r\n        <\/p>\r\n      <\/div>\r\n\r\n      <div class=\"ols-course-feature\">\r\n        <h3>Teacher-marked SAQs<\/h3>\r\n        <p>\r\n          Submit written exam responses and receive chemistry specialist feedback with improvement guidance.\r\n        <\/p>\r\n      <\/div>\r\n\r\n      <div class=\"ols-course-feature\">\r\n        <h3>Progress tracking<\/h3>\r\n        <p>\r\n          Identify strengths and weaknesses across the full 3.3.1 and 3.3.2 specification with targeted reporting.\r\n        <\/p>\r\n      <\/div>\r\n\r\n    <\/div>\r\n\r\n    <div class=\"ols-course-animation-wrap\">\r\n\r\n      <h3 class=\"ols-course-animation-title\">\r\n        See how the course works\r\n      <\/h3>\r\n\r\n      <div class=\"ols-animation-frame-shell\">\r\n        <iframe\r\n          id=\"olsCourseAnimationFrame001\"\r\n          title=\"OLS course preview animation\"\r\n          loading=\"lazy\"\r\n          referrerpolicy=\"no-referrer\">\r\n        <\/iframe>\r\n\r\n        <button\r\n          class=\"ols-animation-start-overlay\"\r\n          id=\"olsCourseAnimationStart001\"\r\n          type=\"button\"\r\n          aria-label=\"Play OLS course preview animation\">\r\n          <span class=\"ols-animation-start-content\">\r\n            <span class=\"ols-animation-play-circle\" aria-hidden=\"true\">\r\n              <span class=\"ols-animation-play-icon\"><\/span>\r\n            <\/span>\r\n            <span class=\"ols-animation-start-text\">\r\n              Play course preview animation\r\n            <\/span>\r\n          <\/span>\r\n        <\/button>\r\n\r\n        <button\r\n          class=\"ols-animation-pause-button\"\r\n          id=\"olsCourseAnimationPause001\"\r\n          type=\"button\"\r\n          aria-label=\"Pause course preview animation\">\r\n          Pause\r\n        <\/button>\r\n      <\/div>\r\n\r\n      <p class=\"ols-course-video-status\">\r\n        Click play to start the course preview animation.\r\n      <\/p>\r\n\r\n    <\/div>\r\n\r\n    <div class=\"ols-course-cta-bottom\">\r\n\r\n      <a class=\"ols-course-button\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/introduction-to-organic-chemistry-and-alkanes-3-3-1-3-3-2-aqa\/\">\r\n        View Introduction to Organic Chemistry and Alkanes Course\r\n      <\/a>\r\n\r\n    <\/div>\r\n\r\n  <\/div>\r\n\r\n  <template id=\"olsCourseAnimationTemplate001\">\r\n<!DOCTYPE html>\r\n<html lang=\"en\">\r\n<head>\r\n<meta charset=\"UTF-8\">\r\n<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">\r\n<title>OLS Combined Promo Animation<\/title>\r\n\r\n<style>\r\n*{box-sizing:border-box;}\r\n\r\nhtml.ols-animation-paused *,\r\nhtml.ols-animation-paused *::before,\r\nhtml.ols-animation-paused *::after{\r\n  animation-play-state:paused!important;\r\n}\r\n\r\n:root{\r\n  --ols-video-screen-w:1180;\r\n  --ols-video-screen-h:664;\r\n  --ols-video-screen-scale:1;\r\n  --ols-mcq-screen-w:1360;\r\n  --ols-mcq-screen-h:1130;\r\n  --ols-mcq-screen-scale:1;\r\n  --ols-saq-screen-w:1360;\r\n  --ols-saq-screen-h:965;\r\n  --ols-saq-screen-scale:1;\r\n}\r\n\r\nhtml,\r\nbody{\r\n  width:100%;\r\n  height:100%;\r\n}\r\n\r\nbody{\r\n  margin:0;\r\n  overflow:hidden;\r\n  font-family:Poppins,Arial,sans-serif;\r\n  background:#e9efff;\r\n}\r\n\r\n.ols-combined-stage{\r\n  position:relative;\r\n  width:100vw;\r\n  height:100vh;\r\n  overflow:hidden;\r\n  background:\r\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\r\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\r\n}\r\n\r\n.ols-scene{\r\n  position:absolute;\r\n  inset:0;\r\n  width:100vw;\r\n  height:100vh;\r\n  opacity:0;\r\n  visibility:hidden;\r\n  pointer-events:none;\r\n}\r\n\r\n.ols-scene.active{\r\n  opacity:1;\r\n  visibility:visible;\r\n  pointer-events:auto;\r\n}\r\n\r\n.ols-scene.fade-out{\r\n  animation:olsSceneFadeOut 0.85s ease forwards;\r\n}\r\n\r\n@keyframes olsSceneFadeOut{\r\n  to{\r\n    opacity:0;\r\n    visibility:hidden;\r\n  }\r\n}\r\n\r\n.ols-title-cursor{\r\n  display:inline-block;\r\n  width:5px;\r\n  height:0.85em;\r\n  background:#1C244B;\r\n  margin-left:8px;\r\n  transform:translateY(8px);\r\n  animation:olsBlink 0.8s infinite;\r\n}\r\n\r\n.cursor{\r\n  display:inline-block;\r\n  width:3px;\r\n  height:28px;\r\n  background:#1c244b;\r\n  margin-left:3px;\r\n  transform:translateY(5px);\r\n  animation:olsBlink 0.8s infinite;\r\n}\r\n\r\n@keyframes olsBlink{\r\n  0%,45%{opacity:1;}\r\n  46%,100%{opacity:0;}\r\n}\r\n\r\n.ols-video-stage,\r\n.ols-mcq-stage,\r\n.ols-saq-stage{\r\n  width:100vw;\r\n  height:100vh;\r\n  display:flex;\r\n  justify-content:center;\r\n  align-items:center;\r\n  padding:0;\r\n  overflow:hidden;\r\n  background:\r\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\r\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\r\n}\r\n\r\n.ols-video-title-screen,\r\n.ols-mcq-intro-screen,\r\n.ols-saq-intro{\r\n  position:absolute;\r\n  inset:0;\r\n  z-index:50;\r\n  display:flex;\r\n  justify-content:center;\r\n  align-items:center;\r\n  background:\r\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\r\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\r\n  opacity:1;\r\n  visibility:visible;\r\n  pointer-events:none;\r\n}\r\n\r\n.ols-video-title-screen.hide{animation:olsVideoTitleFadeOut 0.85s ease forwards;}\r\n.ols-mcq-intro-screen.hide{animation:olsMcqIntroFadeOut 0.85s ease forwards;}\r\n.ols-saq-intro.hide{animation:olsSaqIntroFadeOut 0.85s ease forwards;}\r\n\r\n@keyframes olsVideoTitleFadeOut{to{opacity:0;visibility:hidden;}}\r\n@keyframes olsMcqIntroFadeOut{to{opacity:0;visibility:hidden;}}\r\n@keyframes olsSaqIntroFadeOut{to{opacity:0;visibility:hidden;}}\r\n\r\n.ols-video-title-wrap,\r\n.ols-mcq-intro-title-wrap,\r\n.ols-saq-intro-title-wrap{\r\n  max-width:1250px;\r\n  padding:0 34px;\r\n  text-align:center;\r\n}\r\n\r\n.ols-video-title,\r\n.ols-mcq-intro-title,\r\n.ols-saq-intro-title{\r\n  margin:0;\r\n  font-family:Poppins,Arial,sans-serif;\r\n  font-size:clamp(52px,8vw,124px);\r\n  font-weight:600;\r\n  line-height:1.08;\r\n  color:#1C244B;\r\n  text-shadow:-9px 0 9px rgba(28,36,75,0.16);\r\n  letter-spacing:-0.045em;\r\n}\r\n\r\n#videoTitleText,\r\n#mcqIntroTitleText,\r\n#saqIntroTitleText{\r\n  white-space:pre-wrap;\r\n}\r\n\r\n.ols-video-scene{\r\n  width:100%;\r\n  height:100%;\r\n  display:flex;\r\n  justify-content:center;\r\n  align-items:center;\r\n  opacity:0;\r\n  visibility:hidden;\r\n}\r\n\r\n.ols-video-scene.show{\r\n  visibility:visible;\r\n  animation:olsVideoSceneIn 1s ease forwards;\r\n}\r\n\r\n@keyframes olsVideoSceneIn{to{opacity:1;}}\r\n\r\n.ols-video-scale-wrap{\r\n  width:calc(var(--ols-video-screen-w) * 1px);\r\n  height:calc(var(--ols-video-screen-h) * 1px);\r\n  transform:scale(var(--ols-video-screen-scale));\r\n  transform-origin:center center;\r\n  display:flex;\r\n  justify-content:center;\r\n  align-items:center;\r\n}\r\n\r\n.ols-video-card{\r\n  width:1180px;\r\n  height:664px;\r\n  border-radius:28px;\r\n  overflow:hidden;\r\n  background:#1C244B;\r\n  box-shadow:0 28px 80px rgba(28,36,75,0.28);\r\n  transform:translateY(24px) scale(0.96);\r\n  opacity:0;\r\n}\r\n\r\n.ols-video-scene.show .ols-video-card{\r\n  animation:olsVideoCardIn 1s cubic-bezier(.18,.89,.32,1.12) forwards;\r\n  animation-delay:0.2s;\r\n}\r\n\r\n@keyframes olsVideoCardIn{\r\n  to{\r\n    transform:translateY(0) scale(1);\r\n    opacity:1;\r\n  }\r\n}\r\n\r\n.ols-video-card video{\r\n  display:block;\r\n  width:100%;\r\n  height:100%;\r\n  aspect-ratio:16 \/ 9;\r\n  object-fit:cover;\r\n  border:0;\r\n}\r\n\r\n.ols-mcq-scale-wrap,\r\n.ols-saq-scale-wrap{\r\n  width:calc(var(--ols-mcq-screen-w) * 1px);\r\n  height:calc(var(--ols-mcq-screen-h) * 1px);\r\n  transform:scale(var(--ols-mcq-screen-scale));\r\n  transform-origin:center center;\r\n  display:flex;\r\n  justify-content:center;\r\n  align-items:flex-start;\r\n}\r\n\r\n.ols-saq-scale-wrap{\r\n  width:calc(var(--ols-saq-screen-w) * 1px);\r\n  height:calc(var(--ols-saq-screen-h) * 1px);\r\n  transform:scale(var(--ols-saq-screen-scale));\r\n}\r\n\r\n.ols-mcq-screen{\r\n  width:1360px;\r\n  height:1130px;\r\n  border-radius:22px;\r\n  overflow:hidden;\r\n  background:#eaf0ff;\r\n  box-shadow:0 26px 70px rgba(28,36,75,0.22);\r\n  opacity:0;\r\n  transform:translateY(24px) scale(0.96);\r\n}\r\n\r\n.ols-mcq-screen.show{\r\n  animation:olsMcqScreenEnter 1s ease forwards;\r\n}\r\n\r\n@keyframes olsMcqScreenEnter{\r\n  from{opacity:0;transform:translateY(24px) scale(0.96);}\r\n  to{opacity:1;transform:translateY(0) scale(1);}\r\n}\r\n\r\n.mcq-question-area{\r\n  background:#eaf0ff;\r\n  padding:28px 30px 30px;\r\n  position:relative;\r\n  height:610px;\r\n}\r\n\r\n.mcq-question-lead{\r\n  margin:0 0 14px;\r\n  font-size:24px;\r\n  line-height:1.35;\r\n  color:#111827;\r\n}\r\n\r\n.mcq-ionic-table{\r\n  border-collapse:collapse;\r\n  width:500px;\r\n  margin-bottom:8px;\r\n  font-size:21px;\r\n  color:#111827;\r\n}\r\n\r\n.mcq-ionic-table th,\r\n.mcq-ionic-table td{\r\n  border:1.5px solid #c9ced8;\r\n  padding:12px 18px;\r\n  text-align:center;\r\n}\r\n\r\n.mcq-ionic-table th{\r\n  background:#f2f2f2;\r\n  font-weight:700;\r\n}\r\n\r\n.mcq-ionic-table td{\r\n  background:#eaf0ff;\r\n}\r\n\r\n.mcq-question-main{\r\n  margin:6px 0 28px;\r\n  font-size:24px;\r\n  line-height:1.35;\r\n  color:#111827;\r\n}\r\n\r\n.mcq-options-wrap{\r\n  display:flex;\r\n  flex-direction:column;\r\n  gap:17px;\r\n  max-width:1200px;\r\n}\r\n\r\n.mcq-option-row{\r\n  display:flex;\r\n  align-items:center;\r\n  min-height:34px;\r\n  position:relative;\r\n}\r\n\r\n.mcq-radio{\r\n  width:28px;\r\n  height:28px;\r\n  border-radius:50%;\r\n  border:2px solid #6b7280;\r\n  margin-right:16px;\r\n  background:transparent;\r\n  position:relative;\r\n  flex:0 0 auto;\r\n}\r\n\r\n.mcq-radio::after{\r\n  content:\"\";\r\n  position:absolute;\r\n  inset:5px;\r\n  border-radius:50%;\r\n  background:#6b7280;\r\n  opacity:0;\r\n  transform:scale(0.4);\r\n  transition:opacity 0.25s ease,transform 0.25s ease;\r\n}\r\n\r\n.mcq-option-row.selected .mcq-radio::after{\r\n  opacity:1;\r\n  transform:scale(1);\r\n}\r\n\r\n.mcq-radio-ripple{\r\n  position:absolute;\r\n  left:14px;\r\n  top:50%;\r\n  width:28px;\r\n  height:28px;\r\n  border-radius:50%;\r\n  border:2px solid rgba(28,36,75,0.28);\r\n  transform:translate(-50%,-50%) scale(1);\r\n  opacity:0;\r\n  pointer-events:none;\r\n}\r\n\r\n.mcq-option-row.clicking .mcq-radio-ripple{\r\n  animation:mcqRipple 0.75s ease forwards;\r\n}\r\n\r\n@keyframes mcqRipple{\r\n  0%{opacity:0.65;transform:translate(-50%,-50%) scale(1);}\r\n  100%{opacity:0;transform:translate(-50%,-50%) scale(2.5);}\r\n}\r\n\r\n.mcq-option-label{\r\n  font-size:23px;\r\n  color:#111827;\r\n}\r\n\r\n.mcq-specific-feedback{\r\n  display:inline-flex;\r\n  align-items:center;\r\n  margin-left:18px;\r\n  min-height:38px;\r\n  opacity:0;\r\n  transform:translateX(-8px);\r\n}\r\n\r\n.mcq-specific-feedback.show{\r\n  opacity:1;\r\n  transform:translateX(0);\r\n  transition:opacity 0.35s ease,transform 0.35s ease;\r\n}\r\n\r\n.mcq-cross-icon{\r\n  width:26px;\r\n  height:26px;\r\n  border-radius:50%;\r\n  border:2px solid #d83255;\r\n  color:#d83255;\r\n  display:inline-flex;\r\n  justify-content:center;\r\n  align-items:center;\r\n  font-size:18px;\r\n  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class=\"ols-mcq-scale-wrap\">\r\n        <main id=\"mcqScreen\" class=\"ols-mcq-screen\">\r\n          <section class=\"mcq-question-area\">\r\n            <p class=\"mcq-question-lead\">Some ionic radii are shown.<\/p>\r\n\r\n            <table class=\"mcq-ionic-table\">\r\n              <thead>\r\n                <tr>\r\n                  <th>Ion<\/th>\r\n                  <th>Ionic radius \/ nm<\/th>\r\n                <\/tr>\r\n              <\/thead>\r\n              <tbody>\r\n                <tr><td>Na<sup>+<\/sup><\/td><td>0.102<\/td><\/tr>\r\n                <tr><td>K<sup>+<\/sup><\/td><td>0.138<\/td><\/tr>\r\n                <tr><td>F<sup>\u2212<\/sup><\/td><td>0.133<\/td><\/tr>\r\n                <tr><td>Cl<sup>\u2212<\/sup><\/td><td>0.180<\/td><\/tr>\r\n              <\/tbody>\r\n            <\/table>\r\n\r\n            <p class=\"mcq-question-main\">Which compound has the strongest ionic bonding?<\/p>\r\n\r\n            <div class=\"mcq-options-wrap\">\r\n              <div id=\"mcqWrongOption\" class=\"mcq-option-row\">\r\n                <span class=\"mcq-radio\"><\/span>\r\n                <span class=\"mcq-radio-ripple\"><\/span>\r\n                <span class=\"mcq-option-label\">sodium chloride<\/span>\r\n\r\n                <span id=\"mcqSpecificFeedback\" class=\"mcq-specific-feedback\">\r\n                  <span id=\"mcqCrossIcon\" class=\"mcq-cross-icon\">\u00d7<\/span>\r\n                  <span class=\"mcq-specific-feedback-text\">\r\n                    <span id=\"mcqSpecificText\"><\/span><span id=\"mcqSpecificCursor\" class=\"cursor mcq-specific-cursor\" style=\"display:none;\"><\/span>\r\n                  <\/span>\r\n                <\/span>\r\n              <\/div>\r\n\r\n              <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span class=\"mcq-radio-ripple\"><\/span><span class=\"mcq-option-label\">potassium chloride<\/span><\/div>\r\n              <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span class=\"mcq-radio-ripple\"><\/span><span class=\"mcq-option-label\">sodium fluoride<\/span><\/div>\r\n              <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span class=\"mcq-radio-ripple\"><\/span><span class=\"mcq-option-label\">potassium fluoride<\/span><\/div>\r\n            <\/div>\r\n\r\n            <button id=\"mcqSubmitButton\" class=\"mcq-submit-button\">Submit answer<\/button>\r\n          <\/section>\r\n\r\n          <section id=\"mcqGeneralFeedback\" class=\"mcq-general-feedback\">\r\n            <span id=\"mcqGeneralText\"><\/span><span id=\"mcqGeneralCursor\" class=\"cursor mcq-general-cursor\" style=\"display:none;\"><\/span>\r\n          <\/section>\r\n        <\/main>\r\n      <\/div>\r\n    <\/div>\r\n  <\/section>\r\n\r\n  <section id=\"sceneSaq\" class=\"ols-scene\">\r\n    <div class=\"ols-saq-stage\">\r\n      <div id=\"saqIntro\" class=\"ols-saq-intro\">\r\n        <div 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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        <\/div>\n      <\/section>\n\n<section class=\"ols-related-card\">\n        <h2>Related AQA 3.3 Organic Chemistry Revision Notes<\/h2>\n        <p>Continue building the AQA 3.3 Organic Chemistry 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\/aqa\/3-3-2-alkanes\/crude-oil\/cracking\/\">Cracking<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-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\/aqa\/3-3-2-alkanes\/crude-oil\/reforming\/\">Reforming<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-alkanes\/fuel\/combustion\/\">Alkanes as Fuel<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-3-2-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\/aqa\/3-3-1-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\/aqa\/3-3-1-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\">\n        <style>\n          .ols-attribution-card {\n            background: linear-gradient(135deg, #ffffff, #f8fbff);\n            border: 1px solid rgba(28, 36, 75, 0.14);\n            border-radius: 28px;\n            box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n            padding: 34px;\n            margin-bottom: 24px;\n            overflow: hidden;\n            font-family: Poppins, Arial, sans-serif;\n            box-sizing: border-box;\n          }\n      \n          .ols-attribution-card,\n          .ols-attribution-card * {\n            box-sizing: border-box;\n          }\n      \n          .ols-attribution-card p {\n            margin: 0;\n            font-size: 14px;\n            line-height: 1.65;\n            font-weight: 300;\n            color: #667085;\n          }\n      \n          .ols-attribution-card strong {\n            font-weight: 700;\n            color: #1C244B;\n          }\n      \n          @media (max-width: 760px) {\n            .ols-attribution-card {\n              padding: 24px 18px;\n              border-radius: 22px;\n            }\n          }\n        <\/style>\n      \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. 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