{"id":12505,"date":"2026-10-03T08:33:35","date_gmt":"2026-10-03T07:33:35","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/"},"modified":"2026-10-03T08:36:45","modified_gmt":"2026-10-03T07:36:45","slug":"5-2-2-enthalpy-and-entropy","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/","title":{"rendered":"5.2.2 Enthalpy and Entropy"},"content":{"rendered":"\n<div class=\"ols-ocr522-page\">\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>A Level Chemistry<\/p>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>5.2.2 Enthalpy and Entropy<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/\">5.2.2 Enthalpy and Entropy Overview<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/entropy-and-the-direction-of-change\/\">Entropy and the Direction of Change<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/calculating-entropy-changes\/\">Calculating Entropy Changes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/feasibility-gibbs-energy-and-temperature\/\">Feasibility, Gibbs Energy and Temperature<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/thermodynamic-and-kinetic-stability\/\">Thermodynamic and Kinetic Stability<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Other Sections<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-1-lattice-enthalpy\/\">5.2.1 Lattice Enthalpy<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/3-2-1-enthalpy-changes\/\">3.2.1 Enthalpy Changes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-1-1-how-fast\/\">5.1.1 How Fast?<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/3-1-2-group-2\/\">3.1.2 Group 2<\/a>\n      <\/li>\n      <li>\n        <a 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<\/style>\n\n  <!-- BREADCRUMB BAR -->\n  <div class=\"ols-ocr522-breadcrumb-bar\">\n    <div class=\"ols-ocr522-container\">\n      <nav class=\"ols-ocr522-breadcrumb\" 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\/ocr-a\/\">OCR<\/a> \/\n          <span>5.2.2 Enthalpy and Entropy<\/span>\n        <\/nav>\n    <\/div>\n  <\/div>\n\n  <!-- INTRO -->\n  <section class=\"ols-ocr522-intro\">\n    <div class=\"ols-ocr522-container\">\n      <div class=\"ols-ocr522-intro-inner\">\n        <div>\n          <div class=\"ols-ocr522-eyebrow\">OCR A Level Chemistry A &#8211; Module 5 Physical Chemistry and Transition Elements<\/div>\n          <h1>5.2.2<br>Enthalpy and<br>Entropy<\/h1>\n          <div class=\"ols-ocr522-accent-bar\"><\/div>\n          <p class=\"ols-ocr522-intro-lead\">Section 5.2.2 covers entropy as a measure of the dispersal of energy, the entropy of solids, liquids and gases and of reactions that change the number of gas molecules, calculating the entropy change of a system from standard entropies, feasibility in terms of T\u0394S and \u0394H, the Gibbs\u2019 equation \u0394G = \u0394H \u2212 T\u0394S with calculations, feasibility when \u0394G is negative, and the limits of \u0394G predictions in terms of kinetics.<\/p>\n        <\/div>\n        <div class=\"ols-ocr522-info-grid\">\n          <div class=\"ols-ocr522-info-card\"><div class=\"ols-ocr522-info-card-label\">Exam Paper<\/div><div class=\"ols-ocr522-info-card-value\">Paper 1 &amp; 3<\/div><div class=\"ols-ocr522-info-card-sub\">H432\/01 and H432\/03<\/div><\/div>\n          <div class=\"ols-ocr522-info-card\"><div class=\"ols-ocr522-info-card-label\">Learning Outcomes<\/div><div class=\"ols-ocr522-info-card-value\">5.2.2 (a) &#8211; (f)<\/div><div class=\"ols-ocr522-info-card-sub\">6 learning outcomes<\/div><\/div>\n          <div class=\"ols-ocr522-info-card\"><div class=\"ols-ocr522-info-card-label\">Topic Parts<\/div><div class=\"ols-ocr522-info-card-value\">4 pages<\/div><div class=\"ols-ocr522-info-card-sub\">Revision notes available<\/div><\/div>\n          <div class=\"ols-ocr522-info-card\"><div class=\"ols-ocr522-info-card-label\">Exam Board<\/div><div class=\"ols-ocr522-info-card-value\">OCR A<\/div><div class=\"ols-ocr522-info-card-sub\">H432 (2015 onwards)<\/div><\/div>\n        <\/div>\n      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- TOPIC CARDS -->\n  <section class=\"ols-ocr522-topics\">\n    <div class=\"ols-ocr522-container\">\n      <div class=\"ols-ocr522-section-header\">\n        <h2 class=\"ols-ocr522-section-title\">Revision Notes<\/h2>\n        <p class=\"ols-ocr522-section-sub\">Work through 5.2.2 Enthalpy and Entropy in a structured sequence.<\/p>\n      <\/div>\n      <div class=\"ols-ocr522-cards-grid\">\n\n        <!-- Card 1: Entropy and the Direction of Change -->\n        <a class=\"ols-ocr522-card ols-ocr522-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/entropy-and-the-direction-of-change\/\">\n          <div class=\"ols-ocr522-card-img-wrap\">\n            <div class=\"ols-ocr522-visual ols-ocr522-visual--ox\">\n              <div class=\"ols-ocr522-visual-panel\">\n                <div class=\"ols-ocr522-visual-kicker\">Disorder and dispersal<\/div>\n                <div class=\"ols-ocr522-visual-main\">Entropy<\/div>\n                <div class=\"ols-ocr522-config-line\" aria-hidden=\"true\"><span>S rises: solid, liquid, gas<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr522-card-num\">1<\/div>\n            <span class=\"ols-ocr522-card-status ols-ocr522-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-ocr522-card-body\">\n            <p class=\"ols-ocr522-card-title\">Entropy and the Direction of Change<\/p>\n            <p class=\"ols-ocr522-card-desc\">Entropy: disorder and the dispersal of energy, entropy and temperature, changes of state, dissolving, gas moles and the natural direction of change.<\/p>\n            <span class=\"ols-ocr522-card-cta\">Start revising<svg viewBox=\"0 0 16 16\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M3 8h10M9 4l4 4-4 4\"><\/path><\/svg><\/span>\n          <\/div>\n        <\/a>\n\n        <!-- Card 2: Calculating Entropy Changes -->\n        <a class=\"ols-ocr522-card ols-ocr522-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/calculating-entropy-changes\/\">\n          <div class=\"ols-ocr522-card-img-wrap\">\n            <div class=\"ols-ocr522-visual ols-ocr522-visual--tc\">\n              <div class=\"ols-ocr522-visual-panel\">\n                <div class=\"ols-ocr522-visual-kicker\">\u03a3S(products) \u2212 \u03a3S(reactants)<\/div>\n                <div class=\"ols-ocr522-visual-main\">Entropy<br>Calculations<\/div>\n                <div class=\"ols-ocr522-config-line\" aria-hidden=\"true\"><span>J K\u207b\u00b9 mol\u207b\u00b9, sign and size<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr522-card-num\">2<\/div>\n            <span class=\"ols-ocr522-card-status ols-ocr522-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-ocr522-card-body\">\n            <p class=\"ols-ocr522-card-title\">Calculating Entropy Changes<\/p>\n            <p class=\"ols-ocr522-card-desc\">Entropy calculations: \u0394S from standard entropies, units and worked examples.<\/p>\n            <span class=\"ols-ocr522-card-cta\">Start revising<svg viewBox=\"0 0 16 16\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M3 8h10M9 4l4 4-4 4\"><\/path><\/svg><\/span>\n          <\/div>\n        <\/a>\n\n        <!-- Card 3: Feasibility, Gibbs Energy and Temperature -->\n        <a class=\"ols-ocr522-card ols-ocr522-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/feasibility-gibbs-energy-and-temperature\/\">\n          <div class=\"ols-ocr522-card-img-wrap\">\n            <div class=\"ols-ocr522-visual ols-ocr522-visual--tr\">\n              <div class=\"ols-ocr522-visual-panel\">\n                <div class=\"ols-ocr522-visual-kicker\">\u0394G = \u0394H \u2212 T\u0394S<\/div>\n                <div class=\"ols-ocr522-visual-main\">Feasibility and<br>Temperature<\/div>\n                <div class=\"ols-ocr522-config-line\" aria-hidden=\"true\"><span>T = \u0394H \u00f7 \u0394S<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr522-card-num\">3<\/div>\n            <span class=\"ols-ocr522-card-status ols-ocr522-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-ocr522-card-body\">\n            <p class=\"ols-ocr522-card-title\">Feasibility, Gibbs Energy and Temperature<\/p>\n            <p class=\"ols-ocr522-card-desc\">Feasibility: \u0394G = \u0394H \u2212 T\u0394S, the sign of \u0394G, the effect of temperature and the temperature at which a reaction becomes feasible.<\/p>\n            <span class=\"ols-ocr522-card-cta\">Start revising<svg viewBox=\"0 0 16 16\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M3 8h10M9 4l4 4-4 4\"><\/path><\/svg><\/span>\n          <\/div>\n        <\/a>\n\n        <!-- Card 4: Thermodynamic and Kinetic Stability -->\n        <a class=\"ols-ocr522-card ols-ocr522-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/thermodynamic-and-kinetic-stability\/\">\n          <div class=\"ols-ocr522-card-img-wrap\">\n            <div class=\"ols-ocr522-visual ols-ocr522-visual--ca\">\n              <div class=\"ols-ocr522-visual-panel\">\n                <div class=\"ols-ocr522-visual-kicker\">Feasible is not fast<\/div>\n                <div class=\"ols-ocr522-visual-main\">Thermodynamic and<br>Kinetic Stability<\/div>\n                <div class=\"ols-ocr522-config-line\" aria-hidden=\"true\"><span>\u0394G, E\u2090, diamond and petrol<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr522-card-num\">4<\/div>\n            <span class=\"ols-ocr522-card-status ols-ocr522-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-ocr522-card-body\">\n            <p class=\"ols-ocr522-card-title\">Thermodynamic and Kinetic Stability<\/p>\n            <p class=\"ols-ocr522-card-desc\">Thermodynamic and kinetic stability: feasible but slow reactions, activation energy and the limits of \u0394G and \u0394Stotal predictions.<\/p>\n            <span class=\"ols-ocr522-card-cta\">Start revising<svg viewBox=\"0 0 16 16\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M3 8h10M9 4l4 4-4 4\"><\/path><\/svg><\/span>\n          <\/div>\n        <\/a>\n\n      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- SPECIFICATION -->\n  <section class=\"ols-ocr522-spec-section\">\n    <div class=\"ols-ocr522-container\">\n      <div class=\"ols-ocr522-spec-wrap\">\n        <div class=\"ols-ocr522-spec-pill\">Specification Coverage<\/div>\n        <h2 class=\"ols-ocr522-spec-heading\">5.2.2 Enthalpy and Entropy &#8211; OCR A Level Chemistry A<\/h2>\n        <p class=\"ols-ocr522-spec-intro-text\">The following OCR A learning outcomes state what candidates should be able to do. Wording is taken from the OCR A Level Chemistry A (H432) specification.<\/p>\n        <h3 class=\"ols-ocr522-spec-group-title\">5.2.2 Enthalpy and entropy<\/h3>\n        <div class=\"ols-ocr522-spec-rows\">\n          <div class=\"ols-ocr522-spec-row ols-ocr522-spec-row--light\"><div class=\"ols-ocr522-spec-code\">5.2.2(a)<\/div><div class=\"ols-ocr522-spec-text\">explanation that entropy is a measure of the dispersal of energy in a system which is greater, the more disordered a system<\/div><\/div>\n          <div class=\"ols-ocr522-spec-row ols-ocr522-spec-row--mid\"><div class=\"ols-ocr522-spec-code ols-ocr522-spec-code--mid\">5.2.2(b)<\/div><div class=\"ols-ocr522-spec-text\"><div class=\"ols-ocr522-spec-sub-list\"><div class=\"ols-ocr522-spec-sub-row\"><div class=\"ols-ocr522-spec-sub-code\">(i)<\/div><div class=\"ols-ocr522-spec-sub-text\">explanation of the difference in magnitude of the entropy of a system of solids, liquids and gases<\/div><\/div><div class=\"ols-ocr522-spec-sub-row\"><div class=\"ols-ocr522-spec-sub-code\">(ii)<\/div><div class=\"ols-ocr522-spec-sub-text\">explanation of the difference in magnitude of the entropy of a system for a reaction in which there is a change in the number of gaseous molecules<\/div><\/div><\/div><\/div><\/div>\n          <div class=\"ols-ocr522-spec-row ols-ocr522-spec-row--light\"><div class=\"ols-ocr522-spec-code\">5.2.2(c)<\/div><div class=\"ols-ocr522-spec-text\">calculation of the entropy change of a system, \u0394S, and related quantities for a reaction given the entropies of the reactants and products<\/div><\/div>\n          <div class=\"ols-ocr522-spec-row ols-ocr522-spec-row--mid\"><div class=\"ols-ocr522-spec-code ols-ocr522-spec-code--mid\">5.2.2(d)<\/div><div class=\"ols-ocr522-spec-text\">explanation that the feasibility of a process depends upon the entropy change and temperature in the system, T\u0394S, and the enthalpy change of the system, \u0394H<\/div><\/div>\n          <div class=\"ols-ocr522-spec-row ols-ocr522-spec-row--light\"><div class=\"ols-ocr522-spec-code\">5.2.2(e)<\/div><div class=\"ols-ocr522-spec-text\"><div class=\"ols-ocr522-spec-sub-list\"><div class=\"ols-ocr522-spec-sub-row\"><div class=\"ols-ocr522-spec-sub-code\">i<\/div><div class=\"ols-ocr522-spec-sub-text\">explanation of the free energy change, \u0394G, as: \u0394G = \u0394H \u2212 T\u0394S (the Gibbs&#8217; equation)<\/div><\/div><div class=\"ols-ocr522-spec-sub-row\"><div class=\"ols-ocr522-spec-sub-code\">ii<\/div><div class=\"ols-ocr522-spec-sub-text\">calculations related to the free energy change, \u0394G, using \u0394G = \u0394H \u2212 T\u0394S<\/div><\/div><div class=\"ols-ocr522-spec-sub-row\"><div class=\"ols-ocr522-spec-sub-code\">iii<\/div><div class=\"ols-ocr522-spec-sub-text\">explanation that a process is feasible when \u0394G has a negative value<\/div><\/div><\/div><\/div><\/div>\n          <div class=\"ols-ocr522-spec-row ols-ocr522-spec-row--mid\"><div class=\"ols-ocr522-spec-code ols-ocr522-spec-code--mid\">5.2.2(f)<\/div><div class=\"ols-ocr522-spec-text\">the limitations of predictions made by \u0394G about feasibility, in terms of kinetics<\/div><\/div>\n        <\/div>\n      <\/div>\n    <\/div>\n  <\/section>\n  <script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@graph\": [\n    {\n      \"@type\": \"CollectionPage\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/#webpage\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/5-2-2-enthalpy-and-entropy\/\",\n      \"name\": \"5.2.2 Enthalpy and Entropy | OCR A A Level Chemistry | Online Learning System\",\n      \"description\": \"OCR A A Level Chemistry 5.2.2 Enthalpy and Entropy revision notes: entropy and the direction of change, calculating entropy changes, feasibility, gibbs energy and 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[&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":7117,"menu_order":14,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-12505","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/12505","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/comments?post=12505"}],"version-history":[{"count":1,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/12505\/revisions"}],"predecessor-version":[{"id":12551,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/12505\/revisions\/12551"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/7117"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=12505"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}