{"id":8343,"date":"2026-09-18T12:00:39","date_gmt":"2026-09-18T11:00:39","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/calorimetry-measuring-enthalpy-changes\/"},"modified":"2026-10-04T23:02:16","modified_gmt":"2026-10-04T22:02:16","slug":"calorimetry-measuring-enthalpy-changes","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/calorimetry-measuring-enthalpy-changes\/","title":{"rendered":"Calorimetry: Measuring Enthalpy Changes"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-energetics-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      --gold: #c9973a;\n      --grey-text: #667085;\n      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20px;\n      box-shadow: var(--inner-shadow);\n    }\n.ols-faq-item h3 {\n      margin: 0 0 8px;\n      font-size: 20px;\n      line-height: 1.3;\n      color: var(--navy);\n    }\n.ols-faq-item p {\n      margin: 0;\n      font-size: 16px;\n      line-height: 1.65;\n      color: var(--body-text);\n    }\n.ols-faq-card,\n      .ols-quicksnap-card,\n      .ols-attribution-card {\n        padding: 24px 18px;\n        border-radius: 22px;\n      }\n  <\/style>\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>Topic 6 Energetics<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/\">Topic 6 Overview<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/enthalpy-changes-and-standard-conditions\/\">Enthalpy Changes and Standard Conditions<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/standard-enthalpy-changes\/\">Standard Enthalpy Changes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/calorimetry-measuring-enthalpy-changes\/\">Calorimetry: Measuring Enthalpy Changes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/hess-law-and-enthalpy-cycles\/\">Hess's Law and Enthalpy Cycles<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/bond-enthalpies\/\">Bond Enthalpies<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/cp-2-enthalpy-change-via-hess-law\/\">Core Practical 2<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Other Topics<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-3-bonding-structure\/\">Bonding &amp; Structure<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/\">Alkenes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/\">Intermolecular Forces<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8a-redox-chemistry\/\">Redox Chemistry<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\n\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      .replace(\/\\\/+$\/, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = sidebar.querySelectorAll('a[href]');\r\n    var matched = null;\r\n    var matchedLength = 0;\r\n\r\n    sidebar.querySelectorAll('.active, 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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/\">Topic 6 Energetics<\/a> \/\n<span>Calorimetry: Measuring Enthalpy Changes<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Calorimetry: Measuring Enthalpy Changes<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to measuring enthalpy changes by calorimetry: q = mc\u0394T, converting to kJ mol\u207b\u00b9, the cooling-curve correction, and evaluating errors and assumptions, for Edexcel International A Level Chemistry.<\/p>\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">Exam board: Edexcel International<\/div>\n<div class=\"ols-badge\">Unit 2: WCH12\/01<\/div>\n<div class=\"ols-badge\">Topic 6: Energetics<\/div>\n<\/div>\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        <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\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: Temperature Change, Mass and Moles<\/h2>\n<p>Before you start, check the three GCSE skills this calculation is built from.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"756\"><\/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>The Key Equation: q = mc\u0394T<\/h2>\n<\/div>\n<p>A <strong>calorimetry<\/strong> experiment measures the temperature change of a known mass of water or solution and uses it to calculate the energy transferred:<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key equation:<\/strong> q = m \u00d7 c \u00d7 \u0394T<\/p>\n<\/div>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Symbol<\/th><th>Meaning<\/th><th>Units<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>q<\/strong><\/td><td>energy transferred to or from the surroundings<\/td><td>J<\/td><\/tr>\n<tr><td><strong>m<\/strong><\/td><td>mass of the water or solution being heated or cooled (not the mass of the reactants)<\/td><td>g<\/td><\/tr>\n<tr><td><strong>c<\/strong><\/td><td>specific heat capacity; 4.18 J g\u207b\u00b9 K\u207b\u00b9 for water and dilute solutions<\/td><td>J g\u207b\u00b9 K\u207b\u00b9<\/td><\/tr>\n<tr><td><strong>\u0394T<\/strong><\/td><td>temperature change; a change of 1 K equals a change of 1 \u00b0C<\/td><td>K<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>For dilute aqueous solutions it is assumed that the density is 1.00 g cm\u207b\u00b3, so 50.0 cm\u00b3 of solution has a mass of 50.0 g, and that the specific heat capacity is the same as that of water.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Common mistake:<\/strong> Using the mass of the solid added as m. The energy heats the water or solution, so m is the mass of the liquid.<\/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>From q to the Enthalpy Change<\/h2>\n<\/div>\n<p>q gives the energy for the amounts used in the experiment. To find the enthalpy change in kJ mol\u207b\u00b9:<\/p>\n<ol>\n<li>Calculate q = mc\u0394T in joules.<\/li>\n<li>Calculate the moles of the reactant that is <strong>not in excess<\/strong>.<\/li>\n<li>Divide q by those moles and convert to kJ by dividing by 1000.<\/li>\n<li>Add the sign: <strong>negative<\/strong> if the temperature rose (exothermic), positive if it fell.<\/li>\n<\/ol>\n<p><strong>An endothermic case.<\/strong> 10.11 g of potassium nitrate, KNO\u2083, M = 101.1 g mol\u207b\u00b9, is stirred into 100 g of water and the temperature falls by 8.4 K. q = 100 \u00d7 4.18 \u00d7 8.4 = 3511 J; n = 10.11 \u00f7 101.1 = 0.100 mol; \u0394H = 3511 \u00f7 0.100 = 35 110 J mol\u207b\u00b9 = <strong>+35.1 kJ mol\u207b\u00b9<\/strong>. The temperature fell, so the sign is positive.<\/p>\n\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Both a sign and units are required in the final answer, for example \u0394H = \u221256.8 kJ mol\u207b\u00b9. An answer without a sign is incomplete.<\/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: Follow the Four Steps<\/h2>\n<p>Drag the words and numbers into place to work through a new experiment.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-554\" class=\"h5p-iframe\" data-content-id=\"554\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Calorimetry Drag: An Endothermic Dissolving Experiment\"><\/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>Worked Example 1: Reaction in Solution<\/h2>\n<\/div>\n<p>50.0 cm\u00b3 of 1.00 mol dm\u207b\u00b3 hydrochloric acid is mixed with 50.0 cm\u00b3 of 1.10 mol dm\u207b\u00b3 sodium hydroxide in a polystyrene cup. The temperature rises by 6.8 K. Calculate the enthalpy change of neutralisation.<\/p>\n<ol>\n<li>Mass of solution = 100.0 g; q = 100.0 \u00d7 4.18 \u00d7 6.8 = 2842 J<\/li>\n<li>n(HCl) = 1.00 \u00d7 50.0 \u00f7 1000 = 0.0500 mol and n(NaOH) = 1.10 \u00d7 50.0 \u00f7 1000 = 0.0550 mol; they react in a 1:1 ratio, so the acid runs out first and 0.0500 mol of water forms<\/li>\n<li>\u0394H = \u22122842 \u00f7 0.0500 = \u221256 840 J mol\u207b\u00b9 = <strong>\u221256.8 kJ mol\u207b\u00b9<\/strong><\/li>\n<\/ol>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Add the volumes of both solutions to get the mass heated. Divide by the moles of the reagent that is used up, not the one in excess.<\/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: Mass and Moles<\/h2>\n<p>Decide which mass and which number of moles this experiment needs.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-555\" class=\"h5p-iframe\" data-content-id=\"555\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Calorimetry MCQ: Which Mass and Which Moles?\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Worked Example 2: Combustion of a Fuel<\/h2>\n<\/div>\n<p>Burning 0.460 g of ethanol, C\u2082H\u2085OH, from a spirit burner raises the temperature of 100 g of water in a copper can by 20.0 K. Calculate the enthalpy change of combustion.<\/p>\n<ol>\n<li>q = 100 \u00d7 4.18 \u00d7 20.0 = 8360 J<\/li>\n<li>n(C\u2082H\u2085OH) = 0.460 \u00f7 46.0 = 0.0100 mol<\/li>\n<li>\u0394H = \u22128360 \u00f7 0.0100 = \u2212836 000 J mol\u207b\u00b9 = <strong>\u2212836 kJ mol\u207b\u00b9<\/strong><\/li>\n<\/ol>\n<p>The data book value is \u22121367 kJ mol\u207b\u00b9. The experimental value is far less exothermic because much of the energy heats the air and the can rather than the water, and some ethanol burns incompletely. Combustion calorimetry nearly always underestimates the enthalpy change.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> When asked why an experimental value is less exothermic than the data value, give heat loss to the surroundings first, then incomplete combustion or evaporation of the fuel.<\/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: Four Calculations<\/h2>\n<p>Work each one out in full, with a sign and units, before you flip the card.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-757\" class=\"h5p-iframe\" data-content-id=\"757\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Calorimetry Flip Cards: Four Experiments, Four Enthalpy Changes\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Correcting for Heat Loss: the Cooling Curve<\/h2>\n<\/div>\n<p>In a slower reaction the solution starts losing heat before the maximum temperature is reached, so the highest reading is too low.<\/p><p>The correction is to take readings every minute before and after mixing, plot temperature against time, draw a best-fit line through the cooling points and <strong>extrapolate<\/strong> it back to the time of mixing.<\/p><p>The temperature change is read from the graph at that time.<\/p>\n<p>For example, if both solutions were steady at 20.5 \u00b0C before mixing, the highest reading afterwards was 27.9 \u00b0C and the extrapolated line reached 28.6 \u00b0C at the moment of mixing, then \u0394T is 28.6 \u2212 20.5 = 8.1 K, not the 7.4 K that the highest reading would have given.<\/p>\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\/06\/measuring-temperature-change-accurately.webp\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/measuring-temperature-change-accurately.webp\" alt=\"Graphical explanation of measuring temperature change accurately in calorimetry experiments\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/measuring-temperature-change-accurately.webp\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Extrapolating the cooling line back to the moment of mixing gives the temperature rise that would have been reached with no heat loss.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Remember:<\/strong> Record the starting temperature for a few minutes before mixing; if two solutions are used, measure both and take the mean.<\/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: Read the Graph<\/h2>\n<p>Use the described graph to work out the temperature change that should be used.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-557\" class=\"h5p-iframe\" data-content-id=\"557\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Calorimetry Fill In: Reading the Extrapolated Temperature Rise\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Errors, Assumptions and Technique<\/h2>\n<\/div>\n<p>Questions often ask you to evaluate the method. The main sources of error and the assumptions made are:<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Source<\/th><th>Effect<\/th><th>Improvement<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Heat lost to the surroundings<\/strong><\/td><td>\u0394T too small, so \u0394H not exothermic enough<\/td><td>lid on the cup, insulate, use the cooling-curve correction<\/td><\/tr>\n<tr><td><strong>Heat absorbed by the cup or can<\/strong><\/td><td>ignored in the calculation<\/td><td>use a polystyrene cup, which has a very low heat capacity<\/td><\/tr>\n<tr><td><strong>Solution assumed to have c = 4.18 J g\u207b\u00b9 K\u207b\u00b9 and density 1.00 g cm\u207b\u00b3<\/strong><\/td><td>small systematic error<\/td><td>accept as a stated assumption<\/td><\/tr>\n<tr><td><strong>Incomplete reaction or incomplete combustion<\/strong><\/td><td>less energy released<\/td><td>stir; use excess of one reagent; ensure a good oxygen supply<\/td><\/tr>\n<tr><td><strong>Thermometer resolution<\/strong><\/td><td>large percentage uncertainty in small \u0394T<\/td><td>use a 0.1 \u00b0C thermometer or a larger \u0394T<\/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\/wave-29.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\/wave-29.jpg\" alt=\"Four-panel calorimetry summary: q = mc\u0394T, method, calculation and errors, with c_p named as the SPECIFIC heat capacity.\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/wave-29.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>The calorimetric method in one view: the equation, the practical steps, the calculation and the main limitations.<\/p><\/div>\n<\/div>\n<p>This method is assessed in <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/cp-2-enthalpy-change-via-hess-law\/\">Core Practical 2<\/a>, which uses two measured enthalpy changes and Hess&#8217;s law.<\/p>\n<p><strong>Percentage uncertainty<\/strong> = (uncertainty \u00f7 measurement) \u00d7 100. A temperature change is the difference between two readings, so the uncertainty of the thermometer counts twice: read to \u00b10.1 \u00b0C, \u0394T carries \u00b10.2 \u00b0C, which on the 6.8 K rise above is (0.2 \u00f7 6.8) \u00d7 100 = 2.9 per cent. The larger the temperature change, the smaller that percentage.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> The value is less exothermic than expected because heat is lost to the surroundings, so the measured temperature rise is smaller than the true 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: What Went Wrong?<\/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-556\" class=\"h5p-iframe\" data-content-id=\"556\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Calorimetry Summary: Errors, Assumptions and What to Blame\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">7<\/div>\n<h2>Common Exam Points<\/h2>\n<\/div>\n<h3>Calculate an enthalpy change from a temperature rise<\/h3><p>q = mc\u0394T with the mass of solution, divide by moles of the reagent not in excess, convert to kJ, add a negative sign.<\/p>\n<h3>Explain the extrapolation on a temperature-time graph<\/h3><p>It corrects for heat lost while the reaction is still taking place, giving the temperature at the moment of mixing.<\/p>\n<h3>Suggest why the experimental value differs from the data value<\/h3><p>Heat loss to the surroundings, heat absorbed by the apparatus, incomplete reaction or combustion.<\/p>\n<h3>Do not say<\/h3><p>&#8220;Human error&#8221;; &#8220;m is the mass of the solid&#8221;; an answer with no sign.<\/p>\n<\/article>\n\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Use these quick answers to check the calorimetry calculations and practical points.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>What mass goes into q = mc\u0394T?<\/h3>\n<p>The mass of the water or solution being heated. For dilute solutions, 1 cm\u00b3 is taken to have a mass of 1 g.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is the answer negative when the temperature rises?<\/h3>\n<p>A temperature rise shows energy was released to the surroundings, so the reaction is exothermic and \u0394H is negative.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Which moles do I divide by?<\/h3>\n<p>The moles of the reactant that is not in excess, because that decides how much reaction takes place.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why are experimental values usually less exothermic than data book values?<\/h3>\n<p>Heat is lost to the surroundings and absorbed by the apparatus, so the measured temperature change is smaller than the true value.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why use a polystyrene cup?<\/h3>\n<p>It is a good insulator and has a very low heat capacity, so little energy is lost through it or used to heat it.<\/p>\n<\/div>\n<\/div>\n<\/section>\n<section class=\"ols-related-card\">\n<h2>Related Topic 6 Pages<\/h2>\n<p>Use these pages to connect enthalpy definitions, measurement and calculation methods across the topic.<\/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\/topic-6-energetics\/enthalpy-changes-and-standard-conditions\/\">Enthalpy Changes and Standard Conditions<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/standard-enthalpy-changes\/\">Standard Enthalpy Changes<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/hess-law-and-enthalpy-cycles\/\">Hess&#8217;s Law and Enthalpy Cycles<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/bond-enthalpies\/\">Bond Enthalpies<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/cp-2-enthalpy-change-via-hess-law\/\">CP2 Enthalpy Change via Hess&#8217;s Law<\/a>\n<\/div>\n<\/section>\n<section class=\"ols-attribution-card\">\n        <p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n      <\/section>\n    <\/main>\n  \n\n<script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@graph\": [\n    {\n      \"@type\": \"WebPage\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/calorimetry-measuring-enthalpy-changes\/#webpage\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/calorimetry-measuring-enthalpy-changes\/\",\n      \"name\": \"Calorimetry: Measuring Enthalpy Changes | Topic 6 Energetics | Online Learning System\",\n      \"description\": \"Calorimetry for Edexcel International A Level Chemistry: q = mc\u0394T, enthalpy change per mole, cooling-curve correction and sources of error.\",\n      \"isPartOf\": {\n        \"@id\": 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