{"id":66923,"date":"2026-10-13T10:15:34","date_gmt":"2026-10-13T07:15:34","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=66923"},"modified":"2026-10-13T10:15:34","modified_gmt":"2026-10-13T07:15:34","slug":"standard-entropy-of-reaction-calculator","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/chemistry\/standard-entropy-of-reaction-calculator\/","title":{"rendered":"Standard Entropy of Reaction Calculator"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 id=\"calculator-title\" class=\"text-lg font-display font-bold\">Find \u0394S\u00b0 from Molar Entropies and Stoichiometric Coefficients<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"66923\" data-favorite-title=\"Standard Entropy of Reaction\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/chemistry\/standard-entropy-of-reaction-calculator\/\" data-favorite-excerpt=\"Calculate the standard entropy of reaction \u0394S\u00b0 from tabulated standard molar entropies. Enter the stoichiometric coefficient and S\u00b0 of each reactant and product, pick a unit, and get \u0394S\u00b0 with a full breakdown.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-chemistry-1\">\n    <span class=\"icon icon-shape-star-empty\" aria-hidden=\"true\"><\/span>\n  <\/button>\n  <div class=\"calcdash-favorite__tip\" aria-hidden=\"true\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n  <span class=\"sr-only\" role=\"status\" id=\"favorite-status\"><\/span>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/chemistry\/standard-entropy-of-reaction-calculator\/\" method=\"POST\" class=\"calculator\" id=\"calculator-66923\" data-post=\"66923\"><fieldset class=\"fieldset-input is-2\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field is-single\" id=\"input-1\"><label for=\"field-1\">Reactants \u2014 coefficient and S\u00b0 per species<\/label><textarea id=\"field-1\" name=\"reactants_coefficient_and_s_per_species\">1 191.6; 3 130.7<\/textarea><\/div><div class=\"field is-single\" id=\"input-2\"><label for=\"field-2\">Products \u2014 coefficient and S\u00b0 per species<\/label><textarea id=\"field-2\" name=\"products_coefficient_and_s_per_species\">2 192.8<\/textarea><\/div><div class=\"field is-single\" id=\"input-3\"><label for=\"field-3\">Entropy Unit<\/label><div class=\"grid grid-cols-1\"><select id=\"field-3\" name=\"entropy_unit\"><option value=\"J\" selected>J\/(mol\u00b7K)<\/option><option value=\"cal\">cal\/(mol\u00b7K)<\/option><option value=\"kJ\">kJ\/(mol\u00b7K)<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"66923\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> Standard Entropy of Reaction Results<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Standard Reaction Entropy (\u0394S\u00b0)<\/span><span class=\"result-term\">\u0394S\u00b0<\/span><\/span><span class=\"field-value\" id=\"result-1\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result is-column\" id=\"output-2\"><span class=\"field-title\"><span>Species Contributions<\/span><\/span><span class=\"field-value\" id=\"result-2\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result is-column\" id=\"output-3\"><span class=\"field-title\"><span>Calculation Details<\/span><\/span><span class=\"field-value\" id=\"result-3\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result is-column\" id=\"output-4\"><span class=\"field-title\"><span>About the Standard Entropy of Reaction<\/span><\/span><span class=\"field-value\" id=\"result-4\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><\/div><div class=\"result-actions\"><button type=\"button\" class=\"copy-link\"><svg viewBox=\"0 0 20 20\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M12.232 4.232a2.5 2.5 0 0 1 3.536 3.536l-1.225 1.224a.75.75 0 0 0 1.061 1.06l1.224-1.224a4 4 0 0 0-5.656-5.656l-3 3a4 4 0 0 0 .225 5.865.75.75 0 0 0 .977-1.138 2.5 2.5 0 0 1-.142-3.667l3-3Z\"\/><path d=\"M11.603 7.963a.75.75 0 0 0-.977 1.138 2.5 2.5 0 0 1 .142 3.667l-3 3a2.5 2.5 0 0 1-3.536-3.536l1.225-1.224a.75.75 0 0 0-1.061-1.06l-1.224 1.224a4 4 0 1 0 5.656 5.656l3-3a4 4 0 0 0-.225-5.865Z\"\/><\/svg><span class=\"copy-link__text\">Copy link to this calculation<\/span><\/button><span class=\"sr-only\" role=\"status\" id=\"copy-link-status\"><\/span><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"66923\" aria-live=\"polite\" aria-labelledby=\"calc-reactions-title\"><p id=\"calc-reactions-title\" class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/p><div role=\"group\" aria-labelledby=\"calc-reactions-title\" class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" data-reaction-count=\"helpful\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\udca1 <\/span><span class=\"reaction-description font-medium\">Helpful <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"confused\"><span class=\"reaction-count\" data-reaction-count=\"confused\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude15 <\/span><span class=\"reaction-description font-medium\">Confused <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"disappointed\"><span class=\"reaction-count\" data-reaction-count=\"disappointed\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><div class=\"calcdash-ad not-prose calcdash-ad--calc_result calcdash-ad--in-article\"><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-1721569815777345\" data-ad-slot=\"6317458308\" data-ad-layout=\"in-article\" data-ad-format=\"fluid\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script><\/div>\n<style id=\"wpcoderpro-inline-1\">.formula-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>Standard Entropy of Reaction Formula<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\n\\[ \\Delta S^\\circ = \\sum \\nu \\cdot S^\\circ_{\\text{products}} - \\sum \\nu \\cdot S^\\circ_{\\text{reactants}} \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\( \\Delta S^\\circ \\) \u2014 standard entropy of reaction, in J\/(mol\u00b7K) or the chosen unit<\/li>\n<li>\\( \\nu \\) \u2014 stoichiometric coefficient of each species in the balanced equation<\/li>\n<li>\\( S^\\circ \\) \u2014 standard molar entropy of a species, tabulated at 298.15 K<\/li>\n<\/ul>\n<p>The formula states that because entropy is a state function, the entropy change of a reaction is the total entropy of the products minus the total entropy of the reactants, each weighted by its stoichiometric coefficient.<\/p>\n<p>\r\n<\/section>\n<style id=\"wpcoderpro-inline-459\">.calculation-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section id=\"calculation\" class=\"calculation-box\" aria-labelledby=\"calculation-title\">\r\n\t<div id=\"calculation-title\" class=\"not-prose font-display\"><span class=\"icon icon-unordered-list\" aria-hidden=\"true\"><\/span><h2>Standard Entropy of Reaction \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> the Haber reaction N\u2082(g) + 3H\u2082(g) \u2192 2NH\u2083(g). The tabulated standard molar entropies at 298.15 K are S\u00b0(N\u2082) = 191.6, S\u00b0(H\u2082) = 130.7 and S\u00b0(NH\u2083) = 192.8 J\/(mol\u00b7K). These are the calculator's default values, so you can reproduce the result directly.<\/p>\n<p>\\[ \\sum \\nu \\cdot S^\\circ_{\\text{reactants}} = 1 \\times 191.6 + 3 \\times 130.7 = 583.7 \\text{ J\/(mol\u00b7K)} \\]<\/p>\n<p>\\[ \\sum \\nu \\cdot S^\\circ_{\\text{products}} = 2 \\times 192.8 = 385.6 \\text{ J\/(mol\u00b7K)} \\]<\/p>\n<p>\\[ \\Delta S^\\circ = 385.6 - 583.7 = -198.1 \\text{ J\/(mol\u00b7K)} \\]<\/p>\n<p><strong>Result:<\/strong> \u0394S\u00b0 = \u2212198.1 J\/(mol\u00b7K), i.e. \u22120.1981 kJ\/(mol\u00b7K) or \u221247.35 cal\/(mol\u00b7K). The negative sign reflects that four gas molecules combine into two, so the system becomes more ordered.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the Calculator<\/h2>\n<ol>\n<li>Open a table of standard molar entropies (all values must be from the same table, at 298.15 K) and write down the <strong>balanced<\/strong> chemical equation for your reaction.<\/li>\n<li>For every reactant, enter its stoichiometric coefficient followed by its S\u00b0 value in the field <em>Reactants \u2014 coefficient and S\u00b0 per species<\/em>. Separate species with a semicolon or a new line, e.g. <code>1 191.6; 3 130.7<\/code>.<\/li>\n<li>Do the same for the products in the field <em>Products \u2014 coefficient and S\u00b0 per species<\/em>, e.g. <code>2 192.8<\/code>.<\/li>\n<li>Select the unit of your S\u00b0 values under <em>Entropy Unit<\/em>: J\/(mol\u00b7K), cal\/(mol\u00b7K) or kJ\/(mol\u00b7K). Most standard tables use J\/(mol\u00b7K).<\/li>\n<li>Read the result: \u0394S\u00b0 in your chosen unit, plus a per-species contribution table, a step-by-step calculation and an interpretation of the sign.<\/li>\n<\/ol>\n<h2>What Is the Standard Entropy of Reaction?<\/h2>\n<p>The standard entropy of reaction, \u0394S\u00b0, is the entropy change when a reaction proceeds completely under standard conditions \u2014 by convention 298.15 K and 1 bar, with every species in its standard state. Entropy measures the number of microscopic configurations available to a system, so \u0394S\u00b0 tells you whether the reaction makes the system more disordered (positive \u0394S\u00b0) or more ordered (negative \u0394S\u00b0) on balance.<\/p>\n<p>Because entropy is a state function, \u0394S\u00b0 does not depend on the reaction path; it only depends on the initial and final states. This allows the same Hess-type additivity used for enthalpies: you sum the entropies of the products, subtract the sum for the reactants, and weight each species by its coefficient in the balanced equation. If a reaction can be written as the sum of two others, its \u0394S\u00b0 is the sum of the two individual \u0394S\u00b0 values.<\/p>\n<p>An important difference from enthalpies of formation: standard molar entropies are <em>absolute<\/em> quantities, fixed by the third law of thermodynamics (the entropy of a perfect crystal approaches zero as temperature approaches 0 K). Consequently, S\u00b0 values are always positive \u2014 even for elements in their standard state. Typical values at 298 K: N\u2082 191.6, H\u2082 130.7, NH\u2083 192.8, H\u2082O(g) 188.8, H\u2082O(l) 69.9, C(graphite) 5.7 J\/(mol\u00b7K). Gases carry far more entropy than liquids or solids, which is why the sign of \u0394S\u00b0 for gas-phase reactions usually mirrors the change in the number of gas molecules: more gas molecules on the product side \u2192 positive \u0394S\u00b0; fewer \u2192 negative \u0394S\u00b0.<\/p>\n<p>\u0394S\u00b0 rarely stands alone. Combined with the standard enthalpy of reaction \u0394H\u00b0 and the temperature T, it gives the standard Gibbs free energy change, \\( \\Delta G^\\circ = \\Delta H^\\circ - T\\Delta S^\\circ \\), from which the equilibrium constant follows: \\( K = e^{-\\Delta G^\\circ \/ RT} \\). A reaction that is entropy-driven at high temperature may be unfavorable at low temperature precisely because the \\( T\\Delta S^\\circ \\) term grows with T. You can explore the electrochemical route to K with our <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/electrochemical-equilibrium-constant-calculator\/\">Electrochemical Equilibrium Constant calculator<\/a> or the cell-potential side with the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/standard-cell-potential-calculator\/\">Standard Cell Potential calculator<\/a>.<\/p>\n<h2>Assumptions, Limitations and Practical Tips<\/h2>\n<ul>\n<li><strong>Balanced equation required.<\/strong> The coefficients you enter must match the balanced equation exactly; otherwise \u0394S\u00b0 refers to a different reaction. Doubling all coefficients doubles \u0394S\u00b0.<\/li>\n<li><strong>Consistent data source.<\/strong> All S\u00b0 values must come from the same table \u2014 same temperature (298.15 K) and same standard-state convention (1 bar). Mixing tables can shift the result by a few J\/(mol\u00b7K).<\/li>\n<li><strong>Standard states only.<\/strong> Each species must be in its standard state (pure substance at 1 bar; 1 M for solutes). Use the tabulated value for the correct phase: H\u2082O(g) = 188.8 vs H\u2082O(l) = 69.9 J\/(mol\u00b7K) differ enormously.<\/li>\n<li><strong>Temperature dependence.<\/strong> Tabulated S\u00b0 values apply at 298.15 K. At other temperatures, \u0394S\u00b0 changes through heat-capacity corrections; the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/kirchhoffs-law-of-thermochemistry-calculator\/\">Kirchhoff's Law of Thermochemistry calculator<\/a> handles this adjustment.<\/li>\n<li><strong>Ions in solution.<\/strong> Standard entropies of aqueous ions are relative values (H\u207a is defined as 0 J\/(mol\u00b7K)), so some can be negative. This calculator rejects negative S\u00b0 inputs; for ion-based calculations, tabulate whole neutral salt combinations instead or allow signed relative values in your own spreadsheet.<\/li>\n<li><strong>Sign interpretation.<\/strong> A negative \u0394S\u00b0 does not mean a reaction cannot occur \u2014 spontaneity depends on \u0394G\u00b0, not \u0394S\u00b0 alone. It simply means the system's entropy decreases; the surroundings may more than compensate.<\/li>\n<\/ul>\n<p>Once you have \u0394S\u00b0, the natural next steps are computing \u0394G\u00b0 and K at various temperatures, or checking how a temperature change shifts the entropy of reaction. Both build directly on the value this calculator produces.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Calculate the standard entropy of reaction \u0394S\u00b0 from tabulated standard molar entropies. Enter the stoichiometric coefficient and S\u00b0 of each reactant and product, pick a unit, and get \u0394S\u00b0 with a full breakdown.<\/p>\n","protected":false},"author":3168,"featured_media":0,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[54],"tags":[57],"class_list":["post-66923","post","type-post","status-publish","format-standard","hentry","category-chemistry","tag-reactions"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66923","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/3168"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=66923"}],"version-history":[{"count":1,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66923\/revisions"}],"predecessor-version":[{"id":66924,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66923\/revisions\/66924"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=66923"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=66923"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=66923"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}