{"id":3557,"date":"2026-05-14T08:27:19","date_gmt":"2026-05-14T07:27:19","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/?page_id=3557"},"modified":"2026-06-28T05:53:40","modified_gmt":"2026-06-28T04:53:40","slug":"further-substitution","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-4-organic-chemistry-and-alkanes\/reactions\/further-substitution\/","title":{"rendered":"Further Substitution"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-further-substitution-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, 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td::before {\n        content: attr(data-label);\n        font-weight: 700;\n        color: var(--navy);\n        overflow-wrap: anywhere;\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 4 Organic Chemistry &amp; Alkanes<\/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-international\/topic-4-organic-chemistry-and-alkanes\/hazard-and-risk\/\">Hazard &amp; Risk<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-4-organic-chemistry-and-alkanes\/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-international\/topic-4-organic-chemistry-and-alkanes\/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-international\/topic-4-organic-chemistry-and-alkanes\/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-international\/topic-4-organic-chemistry-and-alkanes\/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-international\/topic-4-organic-chemistry-and-alkanes\/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-international\/topic-4-organic-chemistry-and-alkanes\/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-international\/topic-4-organic-chemistry-and-alkanes\/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-international\/topic-4-organic-chemistry-and-alkanes\/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-international\/topic-4-organic-chemistry-and-alkanes\/organic-chemistry\/ester\/\">Ester<\/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-international\/topic-4-organic-chemistry-and-alkanes\/isomerism\/\">Isomerism<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-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-international\/topic-4-organic-chemistry-and-alkanes\/reactions\/further-substitution\/\">Further Substitution<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\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-international\/topic-5-alkenes\/\">Alkenes<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/\">Energetics<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/\">Intermolecular Forces<\/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 = 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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Edexcel International<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-4-organic-chemistry-and-alkanes\/\">Topic 4 Organic Chemistry &amp; Alkanes<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Reactions of Alkanes<\/a> \/\n        <span>Further Substitution<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Further Substitution<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to further substitution in the free-radical substitution of methane, including excess chlorine, formation of CH<sub>2<\/sub>Cl<sub>2<\/sub>, CHCl<sub>3<\/sub> and CCl<sub>4<\/sub>, and the overall equation for complete chlorination.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Exam board: Edexcel International<\/div>\n          <div class=\"ols-badge\">Topic 4: Organic Chemistry &amp; Alkanes<\/div>\n          <div class=\"ols-badge\">Level: A Level Chemistry<\/div>\n        <\/div>\n\n        <div class=\"ols-author\">\n          <img decoding=\"async\" class=\"ols-author-avatar-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\" alt=\"Dr. Mohammed Al-Fatah\">\n          <div class=\"ols-author-content\">\n            <h2 class=\"ols-author-title\">Written by: Dr. Mohammed Al-Fatah<\/h2>\n            <p class=\"ols-author-description\">Chemistry specialist revision notes for A Level Chemistry.<\/p>\n            <a class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\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              View LinkedIn Profile\n            <\/a>\n          <\/div>\n        <\/div>\n      <\/header>\n\n      <article class=\"ols-note-card soft\" id=\"article\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">1<\/div>\n          <h2>What Is Further Substitution?<\/h2>\n        <\/div>\n\n        <p><strong>Further substitution<\/strong> occurs when the haloalkane product from an earlier free-radical substitution step reacts again with chlorine. This means additional hydrogen atoms are replaced by chlorine atoms.<\/p>\n        <p>In the chlorination of methane, the first substitution forms chloromethane, CH<sub>3<\/sub>Cl. If chlorine is present in excess, CH<sub>3<\/sub>Cl can undergo further substitution to form more highly chlorinated products.<\/p>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> Further substitution is still a free-radical substitution process. The molecule already contains chlorine, but remaining C-H bonds can still be substituted.<\/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>Why Excess Chlorine Causes Further Substitution<\/h2>\n        <\/div>\n\n        <p>When chlorine is present in excess, there are enough chlorine molecules and chlorine radicals for the reaction to continue beyond the first substitution product.<\/p>\n        <p>As more hydrogen atoms are replaced, a mixture of chlorinated products can form. These include dichloromethane, trichloromethane and tetrachloromethane.<\/p>\n\n        <div class=\"ols-definition-box\">\n          <p><strong>Further substitution:<\/strong> continued replacement of hydrogen atoms by halogen atoms after the first substitution product has already formed.<\/p>\n        <\/div>\n\n        <div class=\"ols-warning-box\">\n          <p><strong>Exam focus:<\/strong> Further substitution is most likely when chlorine is in excess. The product mixture becomes less pure because several chlorinated products can form.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card green\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">3<\/div>\n          <h2>Products Formed During Further Substitution<\/h2>\n        <\/div>\n\n        <p>Starting from methane, one hydrogen can be replaced at a time. Each substitution introduces one chlorine atom and forms one molecule of hydrogen chloride.<\/p>\n        <p>The sequence of possible products is shown below.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Stage<\/th>\n                <th>Organic product<\/th>\n                <th>Name<\/th>\n                <th>What has happened?<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Stage\"><strong>First substitution<\/strong><\/td>\n                <td data-label=\"Organic product\">CH<sub>3<\/sub>Cl<\/td>\n                <td data-label=\"Name\">Chloromethane<\/td>\n                <td data-label=\"What has happened?\">One H atom in methane has been replaced by Cl.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Stage\"><strong>Further substitution<\/strong><\/td>\n                <td data-label=\"Organic product\">CH<sub>2<\/sub>Cl<sub>2<\/sub><\/td>\n                <td data-label=\"Name\">Dichloromethane<\/td>\n                <td data-label=\"What has happened?\">A second H atom has been replaced by Cl.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Stage\"><strong>Further substitution<\/strong><\/td>\n                <td data-label=\"Organic product\">CHCl<sub>3<\/sub><\/td>\n                <td data-label=\"Name\">Trichloromethane<\/td>\n                <td data-label=\"What has happened?\">A third H atom has been replaced by Cl.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Stage\"><strong>Complete substitution<\/strong><\/td>\n                <td data-label=\"Organic product\">CCl<sub>4<\/sub><\/td>\n                <td data-label=\"Name\">Tetrachloromethane<\/td>\n                <td data-label=\"What has happened?\">All four H atoms have been replaced by Cl.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Remember:<\/strong> The more excess chlorine present, the greater the chance that chlorinated products undergo further substitution.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Propagation Steps Leading to Further Substitution<\/h2>\n        <\/div>\n\n        <p>Further substitution can be explained using the same propagation logic as the first chlorination step. A chlorine radical removes a hydrogen atom from chloromethane, producing a chloromethyl radical.<\/p>\n        <p>The chloromethyl radical then reacts with chlorine to form dichloromethane and regenerate a chlorine radical.<\/p>\n\n        <div class=\"ols-equation-grid\">\n          <div class=\"ols-equation-box\">\n            <p>CH<sub>3<\/sub>Cl + Cl\u2022 \u2192 HCl + \u2022CH<sub>2<\/sub>Cl<\/p>\n          <\/div>\n\n          <div class=\"ols-equation-box\">\n            <p>\u2022CH<sub>2<\/sub>Cl + Cl<sub>2<\/sub> \u2192 CH<sub>2<\/sub>Cl<sub>2<\/sub> + Cl\u2022<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Why this is propagation:<\/strong> a chlorine radical is used in the first step and regenerated in the second step, so the chain reaction can continue.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card yellow\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>Overall Equations for Further Substitution<\/h2>\n        <\/div>\n\n        <p>Further substitution can be represented using overall equations. Each additional substitution uses one Cl<sub>2<\/sub> molecule and forms one HCl molecule.<\/p>\n\n        <div class=\"ols-equation-grid\">\n          <div class=\"ols-equation-box\">\n            <p>CH<sub>3<\/sub>Cl + Cl<sub>2<\/sub> \u2192 CH<sub>2<\/sub>Cl<sub>2<\/sub> + HCl<\/p>\n          <\/div>\n\n          <div class=\"ols-equation-box\">\n            <p>CH<sub>2<\/sub>Cl<sub>2<\/sub> + Cl<sub>2<\/sub> \u2192 CHCl<sub>3<\/sub> + HCl<\/p>\n          <\/div>\n\n          <div class=\"ols-equation-box\">\n            <p>CHCl<sub>3<\/sub> + Cl<sub>2<\/sub> \u2192 CCl<sub>4<\/sub> + HCl<\/p>\n          <\/div>\n        <\/div>\n\n        <p>If methane is fully chlorinated to tetrachloromethane, all four hydrogen atoms are replaced.<\/p>\n\n        <div class=\"ols-equation-box\">\n          <p>CH<sub>4<\/sub> + 4Cl<sub>2<\/sub> \u2192 CCl<sub>4<\/sub> + 4HCl<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">6<\/div>\n          <h2>Exam Clues and Common Mistakes<\/h2>\n        <\/div>\n\n        <p>Exam questions often test whether you understand why free-radical substitution does not usually give one pure product when chlorine is in excess.<\/p>\n        <p>The key point is that chlorinated products still contain C-H bonds, so they can react further under the same free-radical conditions.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Question clue<\/th>\n                <th>What it means<\/th>\n                <th>Best exam response<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Question clue\"><strong>Chlorine is in excess<\/strong><\/td>\n                <td data-label=\"What it means\">More than one substitution can occur.<\/td>\n                <td data-label=\"Best exam response\">State that further hydrogen atoms can be replaced by chlorine.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Question clue\"><strong>A mixture of products forms<\/strong><\/td>\n                <td data-label=\"What it means\">Different numbers of H atoms have been substituted.<\/td>\n                <td data-label=\"Best exam response\">Name or write formulae such as CH<sub>2<\/sub>Cl<sub>2<\/sub>, CHCl<sub>3<\/sub> and CCl<sub>4<\/sub>.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Question clue\"><strong>Asked for an overall equation<\/strong><\/td>\n                <td data-label=\"What it means\">Show the net reaction, not the radical mechanism.<\/td>\n                <td data-label=\"Best exam response\">For full substitution, write CH<sub>4<\/sub> + 4Cl<sub>2<\/sub> \u2192 CCl<sub>4<\/sub> + 4HCl.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-warning-box\">\n          <p><strong>Common mistake:<\/strong> Do not stop at CH<sub>3<\/sub>Cl when chlorine is in excess. The question is asking you to consider continued substitution and the resulting product mixture.<\/p>\n        <\/div>\n      <\/article>\n\n      <section class=\"ols-h5p-card\">\n        <h2>Check Your Understanding<\/h2>\n        <p>Use these short activities to check excess chlorine, further substitution products, propagation steps and the overall equation for complete chlorination.<\/p>\n\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-148\" class=\"h5p-iframe\" data-content-id=\"148\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"T4.7.4.1 Drag: Termination Key Concepts\"><\/iframe><\/div><\/div>\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-149\" class=\"h5p-iframe\" data-content-id=\"149\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"T4.7.4.2 MCQ: Identify a Termination Step\"><\/iframe><\/div><\/div>\n     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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/organic-chemistry-alkanes-topic-4ab-edexcel-international\/\" aria-label=\"Open the Edexcel International A Level Chemistry Topic 4A\/B Organic Chemistry and Alkanes course page\">\n\n              <div class=\"ols-course-cta-image\">\n                <img decoding=\"async\"\n                  src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/04\/edexcel-international-a-level-chemistry-topic-4a-4b-organic-chemistry-alkanes-course-banner.jpg\"\n                  alt=\"Edexcel International A Level Chemistry Topic 4A\/B Organic Chemistry and Alkanes course banner\"\n                >\n              <\/div>\n\n            <\/a>\n\n            <div class=\"ols-course-cta-content\">\n\n              <div class=\"ols-course-cta-header-row\">\n\n                <div class=\"ols-course-cta-kicker\">\n                  Complete Topic 4A\/B Organic Chemistry &#038; Alkanes Course\n                <\/div>\n\n                <a class=\"ols-course-button ols-course-button-top\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/organic-chemistry-alkanes-topic-4ab-edexcel-international\/\">\n                  View Course\n                <\/a>\n\n              <\/div>\n\n              <h2>\n                Master Organic Chemistry and Alkanes for Edexcel International A Level Chemistry\n              <\/h2>\n\n            <\/div>\n\n          <\/div>\n\n          <div class=\"ols-course-cta-intro-stats\">\n\n            <p class=\"ols-course-cta-intro\">\n              Continue from these free revision notes into the full Topic 4A\/B Organic Chemistry and Alkanes course, with guided video teaching, diagnostic MCQ practice, teacher-marked short-answer questions and a specification assignment with a personalised progress report.\n            <\/p>\n\n            <div class=\"ols-course-cta-stats\">\n\n              <div class=\"ols-course-stat\">\n                <span>Guided learning<\/span>\n                <strong>16 hours<\/strong>\n              <\/div>\n\n              <div class=\"ols-course-stat\">\n                <span>Video lessons<\/span>\n                <strong>430 mins<\/strong>\n              <\/div>\n\n              <div class=\"ols-course-stat\">\n                <span>MCQ practice<\/span>\n                <strong>73 marks<\/strong>\n              <\/div>\n\n              <div class=\"ols-course-stat\">\n                <span>SAQ practice<\/span>\n                <strong>30 marks<\/strong>\n              <\/div>\n\n            <\/div>\n\n          <\/div>\n\n          <div class=\"ols-course-cta-features\">\n\n            <div class=\"ols-course-feature\">\n              <h3>Guided video teaching<\/h3>\n              <p>\n                Learn the chemistry and exam technique through structured video lessons with worked examples and walkthroughs.\n              <\/p>\n            <\/div>\n\n            <div class=\"ols-course-feature\">\n  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initial-scale=1.0\">\n      <title>OLS Combined Promo Animation<\/title>\n\n      <style>\n      *{box-sizing:border-box;}\n\n      html.ols-animation-paused *,\n      html.ols-animation-paused *::before,\n      html.ols-animation-paused *::after{\n        animation-play-state:paused!important;\n      }\n\n      :root{\n        --ols-video-screen-w:1180;\n        --ols-video-screen-h:664;\n        --ols-video-screen-scale:1;\n        --ols-mcq-screen-w:1360;\n        --ols-mcq-screen-h:1130;\n        --ols-mcq-screen-scale:1;\n        --ols-saq-screen-w:1360;\n        --ols-saq-screen-h:965;\n        --ols-saq-screen-scale:1;\n      }\n\n      html,\n      body{\n        width:100%;\n        height:100%;\n      }\n\n      body{\n        margin:0;\n        overflow:hidden;\n        font-family:Poppins,Arial,sans-serif;\n        background:#e9efff;\n      }\n\n      .ols-combined-stage{\n        position:relative;\n        width:100vw;\n        height:100vh;\n        overflow:hidden;\n   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    <p class=\"mcq-question-lead\">Some ionic radii are shown.<\/p>\n\n                  <table class=\"mcq-ionic-table\">\n                    <thead>\n                      <tr>\n                        <th>Ion<\/th>\n                        <th>Ionic radius \/ nm<\/th>\n                      <\/tr>\n                    <\/thead>\n                    <tbody>\n                      <tr><td>Na<sup>+<\/sup><\/td><td>0.102<\/td><\/tr>\n                      <tr><td>K<sup>+<\/sup><\/td><td>0.138<\/td><\/tr>\n                      <tr><td>F<sup>\u2212<\/sup><\/td><td>0.133<\/td><\/tr>\n                      <tr><td>Cl<sup>\u2212<\/sup><\/td><td>0.180<\/td><\/tr>\n                    <\/tbody>\n                  <\/table>\n\n                  <p class=\"mcq-question-main\">Which compound has the strongest ionic bonding?<\/p>\n\n                  <div class=\"mcq-options-wrap\">\n                    <div id=\"mcqWrongOption\" class=\"mcq-option-row\">\n                      <span class=\"mcq-radio\"><\/span>\n                      <span class=\"mcq-radio-ripple\"><\/span>\n                      <span class=\"mcq-option-label\">sodium chloride<\/span>\n\n                      <span id=\"mcqSpecificFeedback\" class=\"mcq-specific-feedback\">\n                        <span id=\"mcqCrossIcon\" class=\"mcq-cross-icon\">\u00d7<\/span>\n                        <span class=\"mcq-specific-feedback-text\">\n                          <span id=\"mcqSpecificText\"><\/span><span id=\"mcqSpecificCursor\" class=\"cursor mcq-specific-cursor\" style=\"display:none;\"><\/span>\n                        <\/span>\n                      <\/span>\n                    <\/div>\n\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>\n                    <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span 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        });\n        },700);\n      }\n\n      startVideoSection();\n      <\/script>\n      <\/body>\n      <\/html>\n        <\/template>\n\n        <script>\n          (function(){\n            var startButton = document.getElementById(\"olsCourseAnimationStart001\");\n            var pauseButton = document.getElementById(\"olsCourseAnimationPause001\");\n            var iframe = document.getElementById(\"olsCourseAnimationFrame001\");\n            var template = document.getElementById(\"olsCourseAnimationTemplate001\");\n\n            if (!startButton || !pauseButton || !iframe || !template) {\n              return;\n            }\n\n            startButton.addEventListener(\"click\", function(){\n              iframe.setAttribute(\"srcdoc\", template.innerHTML);\n              startButton.classList.add(\"is-hidden\");\n              pauseButton.classList.add(\"is-visible\");\n              pauseButton.textContent = \"Pause\";\n              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continued substitution in free-radical chlorination.<\/p>\n\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>What is further substitution?<\/h3>\n            <p>Further substitution is the continued replacement of hydrogen atoms by chlorine atoms after the first substitution product has already formed.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why does excess chlorine lead to further substitution?<\/h3>\n            <p>Excess chlorine provides enough chlorine molecules and chlorine radicals for chlorinated products such as CH<sub>3<\/sub>Cl to react again, replacing more hydrogen atoms.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Which products can form when methane reacts with excess chlorine?<\/h3>\n            <p>A mixture may form, including CH<sub>3<\/sub>Cl, CH<sub>2<\/sub>Cl<sub>2<\/sub>, CHCl<sub>3<\/sub> and CCl<sub>4<\/sub>, depending on how many hydrogen atoms are replaced.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What is the overall equation for complete chlorination of methane?<\/h3>\n            <p>The overall equation is CH<sub>4<\/sub> + 4Cl<sub>2<\/sub> \u2192 CCl<sub>4<\/sub> + 4HCl.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why is a mixture of products formed?<\/h3>\n            <p>A mixture forms because partially chlorinated products still contain C-H bonds, so they can undergo further free-radical substitution.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Continue your revision with the linked areas of free-radical substitution and alkane chemistry.<\/p>\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Free Radical Substitution<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Initiation<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Propagation<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Termination<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Combustion<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/alkene-bonding\/\">Alkenes<\/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: 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