{"id":1283,"date":"2024-08-17T10:20:45","date_gmt":"2024-08-17T10:20:45","guid":{"rendered":"https:\/\/www.meniit.com\/study-material\/?p=1283"},"modified":"2024-09-10T11:14:36","modified_gmt":"2024-09-10T11:14:36","slug":"thermodynamic","status":"publish","type":"post","link":"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic","title":{"rendered":"Thermodynamics"},"content":{"rendered":"<h2 style=\"text-align: justify;\">SECTION 1 : SOME BASIC TERMS OF THERMODYNAMICS<\/h2>\n<ol>\n<li style=\"text-align: justify;\"><strong>System :<\/strong> A system is defined as that part of the universe which is under investigation.<\/li>\n<li style=\"text-align: justify;\"><strong>Surroundings :<\/strong> The part of the universe other than the system is known as surroundings<\/li>\n<\/ol>\n<p style=\"text-align: center;\">Universe = System + Surroundings<\/p>\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_69_1 counter-hierarchy ez-toc-counter ez-toc-light-blue ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#TYPES-OF-SYSTEMS\" title=\"TYPES OF SYSTEMS\">TYPES OF SYSTEMS<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#HEAT-Q\" title=\"HEAT (Q)\">HEAT (Q)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#WORK-W\" title=\"WORK (W)\">WORK (W)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#Pressure-Volume-Work\" title=\"Pressure-Volume Work\">Pressure-Volume Work<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#INTERNAL-ENERGY\" title=\"INTERNAL ENERGY\">INTERNAL ENERGY<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#Characteristics-of-Internal-Energy\" title=\"Characteristics of Internal Energy\">Characteristics of Internal Energy<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#MATHEMATICAL-FORMULATION-OF-THE-FIRST-LAW-OF-THERMODYNAMICS\" title=\"MATHEMATICAL FORMULATION OF THE FIRST LAW OF THERMODYNAMICS\">MATHEMATICAL FORMULATION OF THE FIRST LAW OF THERMODYNAMICS<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#CALCULATION-OF-WORK-DONE-W\" title=\"CALCULATION OF WORK DONE (W)\">CALCULATION OF WORK DONE (W)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#SECTION-6-ENTROPY-S\" title=\"SECTION 6 : ENTROPY (S)\">SECTION 6 : ENTROPY (S)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#SOME-IMPORTANT-POINTS-RELATED-TO-ENTROPY\" title=\"SOME IMPORTANT POINTS RELATED TO ENTROPY\">SOME IMPORTANT POINTS RELATED TO ENTROPY<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#SECTION-7-SECOND-LAW-OF-THERMODYNAMICS\" title=\"SECTION 7 : SECOND LAW OF THERMODYNAMICS\">SECTION 7 : SECOND LAW OF THERMODYNAMICS<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#STATEMENT-OF-SECOND-LAW-OF-THERMODYNAMICS\" title=\"STATEMENT OF SECOND LAW OF THERMODYNAMICS\">STATEMENT OF SECOND LAW OF THERMODYNAMICS<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#SECTION-8-SPONTANEOUS-PROCESSES\" title=\"SECTION 8 : SPONTANEOUS PROCESSES\">SECTION 8 : SPONTANEOUS PROCESSES<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#SOME-IMPORTANT-POINTS-RELATED-TO-SPONTANEOUS-CHANGES\" title=\"SOME IMPORTANT POINTS RELATED TO SPONTANEOUS CHANGES\">SOME IMPORTANT POINTS RELATED TO SPONTANEOUS CHANGES<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-15\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#SECTION-9-FREE-ENERGY-G\" title=\"SECTION 9 : FREE ENERGY (G)\">SECTION 9 : FREE ENERGY (G)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-16\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#FREE-ENERGY-CHANGE-AND-THE-NATURE-OF-PROCESS\" title=\"FREE ENERGY CHANGE AND THE NATURE OF PROCESS\">FREE ENERGY CHANGE AND THE NATURE OF PROCESS<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-17\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#SECTION-10-THERMOCHEMISTRY\" title=\"SECTION 10 : THERMOCHEMISTRY\">SECTION 10 : THERMOCHEMISTRY<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-18\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#SECTION-11-HESSS-LAW-OF-CONSTANT-HEAT-SUMMATION\" title=\"SECTION 11 : HESS\u2019S LAW OF CONSTANT HEAT SUMMATION\">SECTION 11 : HESS\u2019S LAW OF CONSTANT HEAT SUMMATION<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-19\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\/#SECTION-12-BOND-ENERGY-OR-BOND-ENTHALPY\" title=\"SECTION 12 : BOND ENERGY OR BOND ENTHALPY\">SECTION 12 : BOND ENERGY OR BOND ENTHALPY<\/a><\/li><\/ul><\/nav><\/div>\n<h3><span class=\"ez-toc-section\" id=\"TYPES-OF-SYSTEMS\"><\/span>TYPES OF SYSTEMS<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\"><strong>Isolated System :<\/strong> A system that cannot exchange mass and\/or energy with the surroundings.\u00a0 For example : ice, milk or any other liquid kept in a thermos flask.<\/p>\n<p style=\"text-align: justify;\"><strong>Closed System :<\/strong> It exchanges only energy with the surroundings. For example :<\/p>\n<ul>\n<li style=\"text-align: justify;\">Water in closed bottle (boundaries of closed system act as conductor of heat)<\/li>\n<li style=\"text-align: justify;\">Heating of CaCO<sub>3<\/sub> in sealed tube, etc.<\/li>\n<\/ul>\n<p style=\"text-align: justify;\"><strong>Open System :<\/strong> It exchanges energy and mass both with the surroundings.<\/p>\n<p style=\"text-align: justify;\">For example : Trees in forest, tea in an open cup, etc.<\/p>\n<p style=\"text-align: justify;\"><strong>Macro System :<\/strong> A very large number of molecules\/atoms are present in this system. Properties of<br \/>\na macro system are called macro properties.<\/p>\n<p style=\"text-align: justify;\">For example : Pressure, temperature, density, composition, viscosity, surface tension, colour,<br \/>\nrefractive index, etc.<\/p>\n<p style=\"text-align: justify;\"><strong>State of System :<\/strong> The system in which the values of macro properties are definite. It is said to be<br \/>\nin definite state. Thus, the state of system is determined by its macro properties.<\/p>\n<p style=\"text-align: justify;\"><strong>State Functions :<\/strong> The properties of a system which depend only on initial and final states, and do<br \/>\nnot depend on its path.<\/p>\n<p style=\"text-align: justify;\">For example : Free energy, enthalpy, internal energy, etc.<\/p>\n<p style=\"text-align: justify;\"><strong>Extensive Property :<\/strong> The property which depends on the amount of substance present in the<br \/>\nsystem.<\/p>\n<p style=\"text-align: justify;\">For example : Mass volume, Heat capacity, Entropy, Enthalpy, Free energy, Internal energy etc.<\/p>\n<p style=\"text-align: justify;\"><strong>Intensive Property :<\/strong> These do not depend on the amount of substance present in the system.<\/p>\n<p style=\"text-align: justify;\">For example : Temperature, Density, Viscosity, Melting point, Boiling point, Surface tension,<br \/>\nRefractive index. etc.<\/p>\n<h2>SECTION 2 : THERMODYNAMIC PARAMETERS<\/h2>\n<h3 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"HEAT-Q\"><\/span>HEAT (Q)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">The energy transferred from hotter body to colder body is known as heat. If heat is given to the<br \/>\nsystem Q &gt; 0. If heat is released from system Q &lt; 0.<\/p>\n<h3 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"WORK-W\"><\/span>WORK (W)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">Work done by system \u21d2 W &lt; 0, W = \u2013ve<\/p>\n<p style=\"text-align: justify;\">Work done on the system \u21d2 W &gt; 0, W = +ve<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Pressure-Volume-Work\"><\/span>Pressure-Volume Work<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">Consider a cylinder fitted with a frictionless and weightless piston having area of cross section A. Let the pressure acting on the piston be P(external pressure), which is slightly less than the internal pressure of gas. Suppose the gas expands a little and piston is pushed out a small distance dx. The work done by the gas on the piston will be<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1286 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/diagram-5.png\" alt=\"diagram\" width=\"508\" height=\"223\" srcset=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/diagram-5.png 508w, https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/diagram-5-300x132.png 300w\" sizes=\"auto, (max-width: 508px) 100vw, 508px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1462 size-full aligncenter\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-73.png\" alt=\"formula\" width=\"661\" height=\"174\" srcset=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-73.png 661w, https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-73-300x79.png 300w\" sizes=\"auto, (max-width: 661px) 100vw, 661px\" \/><\/p>\n<p style=\"text-align: justify;\">If the volume of gas changes from V<sub>1<\/sub> to V<sub>2<\/sub> then total work done W will be given by<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1288 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-19.png\" alt=\"formula\" width=\"154\" height=\"79\" \/><\/p>\n<p style=\"text-align: justify;\">If the external pressure P against which the gas expands remains almost constant throughout the process then<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1289 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-20.png\" alt=\"formula\" width=\"288\" height=\"88\" \/><\/p>\n<p>According to latest SI convention :<\/p>\n<ul>\n<li style=\"text-align: justify;\">Work is taken as negative when work is done by the system on the surrounding as in expansion of gas<\/li>\n<\/ul>\n<p style=\"text-align: center;\">\u2206W = \u2013P\u2206V<\/p>\n<ul>\n<li style=\"text-align: justify;\">Work is taken as positive when work is done on the system as in contraction of gas<\/li>\n<\/ul>\n<p style=\"text-align: center;\">\u2206W = P\u2206V<\/p>\n<h3><span class=\"ez-toc-section\" id=\"INTERNAL-ENERGY\"><\/span>INTERNAL ENERGY<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>The total energy contained in a system is called its internal energy or intrinsic energy. This is denoted by a symbol E or U. Change in internal energy = \u2206E.<\/p>\n<p>If internal energy is increased \u21d2 \u2206E &gt; 0\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 [\u2206E = positive]<\/p>\n<p>If internal energy is decreased \u21d2 \u2206E &gt; 0\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0[\u2206E = negative]<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Characteristics-of-Internal-Energy\"><\/span>Characteristics of Internal Energy<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<ol>\n<li style=\"text-align: justify;\">The fixed amount of energy contained in a substance is called its internal energy.<\/li>\n<li style=\"text-align: justify;\">Internal energy is present in all the substances.<\/li>\n<li style=\"text-align: justify;\">Quantitative Property : Internal energy depends on chemical nature, pressure, temperature and volume of the substance.<\/li>\n<li style=\"text-align: justify;\">State Functions : Internal energy depends on the physical state of the system.<\/li>\n<li style=\"text-align: justify;\">Internal energy is the total of all types of energy, e.g., potential energy, kinetic energy, vibrational energy, rotational energy, etc.<\/li>\n<li style=\"text-align: justify;\">Absolute value of internal energy cannot be determined. Only change in internal energy (\u2206E) can be determined.<\/li>\n<\/ol>\n<p style=\"text-align: justify;\">\u2206E = Energy in final state \u2013 Energy in initial state<\/p>\n<p style=\"text-align: justify;\">\u2206E = E<sub>2<\/sub> \u2013 E<sub>1<\/sub><\/p>\n<p style=\"text-align: justify;\">\u2206E = Sum of energy of the products \u2013 Sum of energy of reactants<\/p>\n<ul>\n<li style=\"text-align: justify;\">Internal energy is an extensive property.<\/li>\n<li style=\"text-align: justify;\">In most stable form, internal energy of the system is regarded as zero.<\/li>\n<\/ul>\n<h2>SECTION 4 : FIRST LAW OF THERMODYNAMICS<\/h2>\n<p style=\"text-align: justify;\">Energy can neither be produced nor destroyed, it can only be changed from one form to the other, i.e.,<\/p>\n<ol>\n<li style=\"text-align: justify;\">Total energy of an isolated system remains constant.<\/li>\n<li style=\"text-align: justify;\">Total energy of universe remains constant.<\/li>\n<li style=\"text-align: justify;\">Whenever some amount of any form of energy disappears, the same amount of energy of other form is produced.<\/li>\n<\/ol>\n<h3><span class=\"ez-toc-section\" id=\"MATHEMATICAL-FORMULATION-OF-THE-FIRST-LAW-OF-THERMODYNAMICS\"><\/span>MATHEMATICAL FORMULATION OF THE FIRST LAW OF THERMODYNAMICS<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">Let, Initial internal energy of the system = E<sub>1<\/sub><\/p>\n<p style=\"text-align: justify;\">Heat supplied to the system = q<\/p>\n<p style=\"text-align: justify;\">Work done on the system = w<\/p>\n<p style=\"text-align: justify;\">Final internal energy of the system = E<sub>2<\/sub><\/p>\n<p style=\"text-align: justify;\">According first law of thermodynamics<\/p>\n<p style=\"text-align: justify;\">E<sub>2<\/sub> = E<sub>1<\/sub> + q + w<\/p>\n<p style=\"text-align: justify;\">E<sub>2<\/sub> \u2013 E<sub>1<\/sub> = q + w<\/p>\n<p style=\"text-align: justify;\">\u2206E = q + w<\/p>\n<h3><span class=\"ez-toc-section\" id=\"CALCULATION-OF-WORK-DONE-W\"><\/span>CALCULATION OF WORK DONE (W)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">For any expansion against external pressure p<sub>ext<\/sub> ;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1293 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-21.png\" alt=\"formula\" width=\"151\" height=\"70\" \/><\/p>\n<p style=\"text-align: justify;\"><strong>Case 1 :<\/strong> When V is constant (Isochoric process)<\/p>\n<p style=\"text-align: center;\">w = 0, q<sub>v<\/sub> = \u2206E<\/p>\n<p style=\"text-align: justify;\"><strong>Case 2 :<\/strong> When p<sub>ext<\/sub> is constant (isobaric process)<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1294 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-22.png\" alt=\"formula\" width=\"162\" height=\"62\" \/><\/p>\n<p style=\"text-align: justify;\">If process is reversible and isobaric, i.e., p<sub>ext<\/sub> = P<sub>gas<\/sub> = constant<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1297 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-23.png\" alt=\"formula\" width=\"209\" height=\"58\" \/><\/p>\n<p style=\"text-align: justify;\"><strong>Case 3 :<\/strong> When T is constant (Isothermal expansion)<\/p>\n<p style=\"text-align: justify;\"><strong>Case (a) :<\/strong> When process is irreversible isothermal and p<sub>ext<\/sub> is constant.<\/p>\n<p style=\"text-align: center;\">w = \u2013 p<sub>ext<\/sub>\u2206V<\/p>\n<p style=\"text-align: justify;\"><strong>Case (b) :<\/strong> When process is reversible and isothermal.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1298 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-24.png\" alt=\"formula\" width=\"388\" height=\"58\" srcset=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-24.png 388w, https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-24-300x45.png 300w\" sizes=\"auto, (max-width: 388px) 100vw, 388px\" \/><\/p>\n<p style=\"text-align: justify;\"><strong>Important Fact :<\/strong> During isothermal expansion for a sample of ideal gas \u2206E = 0.<\/p>\n<p style=\"text-align: justify;\"><strong>Case 4 :<\/strong> When q = 0, i.e., (adiabatic reversible process)<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1299 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/thermodynamics-functions.png\" alt=\"thermodynamics functions\" width=\"634\" height=\"362\" srcset=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/thermodynamics-functions.png 634w, https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/thermodynamics-functions-300x171.png 300w\" sizes=\"auto, (max-width: 634px) 100vw, 634px\" \/><\/p>\n<h3><span class=\"ez-toc-section\" id=\"SECTION-6-ENTROPY-S\"><\/span>SECTION 6 : ENTROPY (S)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">It is a thermodynamic property and is a measure of disorderliness or randomness of a system, i.e., greater the disorder in a system, higher is the entropy of that system.<\/p>\n<p style=\"text-align: center;\">Solid &lt; Liquid &lt; Gas<\/p>\n<p style=\"text-align: justify;\">Entropy is a state function and does not depend on path.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1302 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-25.png\" alt=\"formula\" width=\"519\" height=\"116\" srcset=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-25.png 519w, https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-25-300x67.png 300w\" sizes=\"auto, (max-width: 519px) 100vw, 519px\" \/><\/p>\n<h3><span class=\"ez-toc-section\" id=\"SOME-IMPORTANT-POINTS-RELATED-TO-ENTROPY\"><\/span>SOME IMPORTANT POINTS RELATED TO ENTROPY<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li style=\"text-align: left;\">Entropy change, \u2206S = S (Final state) \u2013 S (Initial state)<\/li>\n<li style=\"text-align: left;\">Among states of matter, entropy of solid &gt; liquid &gt; gas.<\/li>\n<li style=\"text-align: left;\">Reactions involving increase in overall moles generally show increase in entropy.<\/li>\n<li style=\"text-align: left;\">When a solute gets dissolved a solvent, the entropy increases.<\/li>\n<li style=\"text-align: left;\">When the number of gaseous products increases in a chemical reaction, the entropy also increases.<br \/>\nFor example.<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<p style=\"text-align: center;\">(NH<sub>4<\/sub>)<sub>2<\/sub>S (s) \u2192 2NH<sub>3<\/sub> (g) + H<sub>2<\/sub>S (g)<\/p>\n<ol style=\"text-align: center;\" start=\"6\">\n<li>NH<sub>3<\/sub> (g) + HCl (g) \u2192 NH<sub>4<\/sub>Cl (s) Entropy is decreasing.<\/li>\n<li style=\"text-align: left;\">For a reaction, change in entropy \u2206S = Sum of entropies of the products \u2013 Sum of entropies of the reactants.<\/li>\n<li style=\"text-align: left;\">From the formula given above, unit of entropy is Joule kelvin<sup>\u20131<\/sup> mole<sup>\u20131<\/sup>.<\/li>\n<li style=\"text-align: left;\">At equilibrium, \u2206S<sub>universe<\/sub> for the process is zero.<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<h3><span class=\"ez-toc-section\" id=\"SECTION-7-SECOND-LAW-OF-THERMODYNAMICS\"><\/span>SECTION 7 : SECOND LAW OF THERMODYNAMICS<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<ol>\n<li style=\"text-align: justify;\">The first law of thermodynamics does not help us to predict the direction of the change. The answer to this problem is provided by second law of thermodynamics. The statement of the law is developed in terms of the entropy criterion.<\/li>\n<li style=\"text-align: justify;\">The second law of thermodynamics introduces the concept of entropy and its relation with spontaneous processes.<\/li>\n<li style=\"text-align: justify;\">In an isolated system such as mixing of gases, there is no exchange of energy or matter between the system and the surroundings. But due to increase in randomness, there is increase in entropy. Thus, we can say that for a spontaneous process in an isolated system, the change in entropy is positive. i.e., \u2206S &gt; 0.<\/li>\n<li style=\"text-align: justify;\">However, if the system is not isolated, we have to take into account the entropy changes of the system and the surroundings. Then, the total entropy change (\u2206S<sub>total<\/sub>) will be equal to the sum of the change in entropy of the system (\u2206S<sub>system<\/sub>) and the change in entropy of the surroundings (\u2206S<sub>surrounding<\/sub>), i.e.,<\/li>\n<\/ol>\n<p style=\"text-align: center;\">\u2206S<sub>total<\/sub> = \u2206S<sub>system<\/sub> + \u2206S<sub>surroundings<\/sub><\/p>\n<ol style=\"text-align: justify;\" start=\"5\">\n<li style=\"text-align: justify;\">For a spontaneous process, \u2206S<sub>total<\/sub> must be positive, i.e.,<\/li>\n<\/ol>\n<p style=\"text-align: center;\">\u2206S<sub>total<\/sub> = \u2206S<sub>system<\/sub> + \u2206S<sub>surroundings<\/sub> &gt; 0<\/p>\n<ol style=\"text-align: justify;\" start=\"6\">\n<li style=\"text-align: justify;\">But system and surroundings constitute universe for thermodynamic point of view so that for spontaneous change<\/li>\n<\/ol>\n<p style=\"text-align: center;\">\u2206S<sub>universe<\/sub> &gt; 0<\/p>\n<h3><span class=\"ez-toc-section\" id=\"STATEMENT-OF-SECOND-LAW-OF-THERMODYNAMICS\"><\/span>STATEMENT OF SECOND LAW OF THERMODYNAMICS<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">This states that the entropy of the universe always increases in every spontaneous (natural) change.<\/p>\n<p style=\"text-align: justify;\">Thus, combining the first and second law of thermodynamics, the combined statement becomes :<\/p>\n<p style=\"text-align: justify;\">The energy of the universe is conserved whereas the entropy of the universe always increases in any natural process.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"SECTION-8-SPONTANEOUS-PROCESSES\"><\/span>SECTION 8 : SPONTANEOUS PROCESSES<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">This type of physical and chemical change occurs of its own under specific circumstances or on proper initiation.<\/p>\n<p style=\"text-align: justify;\"><strong>Examples :<\/strong><\/p>\n<ol>\n<li style=\"text-align: justify;\">Flow of liquids from higher to lower level.<\/li>\n<li style=\"text-align: justify;\">Flow of gases from higher pressure to lower pressure.<\/li>\n<li style=\"text-align: justify;\">Conduction of heat from hot body to the colder body.<\/li>\n<li style=\"text-align: justify;\">Flow of electric current from higher potential to lower potential.<\/li>\n<li style=\"text-align: justify;\">Dissolution of sugar in water.<\/li>\n<li style=\"text-align: justify;\">All naturally occurring processes.<\/li>\n<li style=\"text-align: justify;\">Burning of coal and other fuels.<\/li>\n<\/ol>\n<h3><span class=\"ez-toc-section\" id=\"SOME-IMPORTANT-POINTS-RELATED-TO-SPONTANEOUS-CHANGES\"><\/span>SOME IMPORTANT POINTS RELATED TO SPONTANEOUS CHANGES<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<ul>\n<li style=\"text-align: justify;\">These changes occur only in single direction. They do not occur in opposite direction by themselves. For example. water does not flow itself from lower to upper level.<\/li>\n<li style=\"text-align: justify;\">Work can be done by a spontaneous change. For example, motion of a piston by expansion of gas, rotation of a wheel when water falls on it from some height, etc.<\/li>\n<li style=\"text-align: justify;\">For a spontaneous change for an isolated system, \u2206S is positive.<\/li>\n<li style=\"text-align: justify;\">When system is not isolated.<\/li>\n<\/ul>\n<p style=\"text-align: center;\">\u2206S<sub>(total)<\/sub> = \u2206S<sub>(system)<\/sub> + \u2206S<sub>(surrounding)<\/sub> &gt; 0<\/p>\n<ul>\n<li>Change in entropy of a system<\/li>\n<\/ul>\n<p style=\"text-align: center;\">\u2206S<sub>(Surroundings)<\/sub> = q (Reversible)\/T<\/p>\n<h3><span class=\"ez-toc-section\" id=\"SECTION-9-FREE-ENERGY-G\"><\/span>SECTION 9 : FREE ENERGY (G)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">The available amount of energy during the process in the system which can be changed into maximum useful work, is called free energy of the system.<\/p>\n<p style=\"text-align: justify;\">Thus, free energy change in the system (\u2206G), is the measure of the capability of doing useful work by the system.<\/p>\n<p style=\"text-align: center;\">G = H \u2013 TS (Gibbs-Helmholtz equation)<\/p>\n<p style=\"text-align: justify;\">At constant temperature Gibb\u2019s free energy change<\/p>\n<p style=\"text-align: center;\">\u2206G = \u2206H \u2013 T\u2206S<\/p>\n<p style=\"text-align: center;\">If\u00a0 \u00a0\u2206G &lt; 0, then the reaction is spontaneous<\/p>\n<p style=\"text-align: center;\">\u2206G = 0, reaction has achieved quilibrium<\/p>\n<p style=\"text-align: center;\">\u2206G &gt; 0, then the reaction is non-spontaneous<\/p>\n<h3><span class=\"ez-toc-section\" id=\"FREE-ENERGY-CHANGE-AND-THE-NATURE-OF-PROCESS\"><\/span>FREE ENERGY CHANGE AND THE NATURE OF PROCESS<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<table style=\"height: 228px;\" width=\"735\">\n<tbody>\n<tr>\n<th class=\"thhead\" width=\"37\">D<strong>H<\/strong><\/th>\n<th class=\"thhead\" width=\"42\">D<strong>S<\/strong><\/th>\n<th class=\"thhead\" width=\"129\">D<strong>G = <\/strong>D<strong>H \u2013 T<\/strong>D<strong>S<\/strong><\/th>\n<th class=\"thhead\" width=\"121\"><strong>Remarks<\/strong><\/th>\n<\/tr>\n<tr>\n<td style=\"text-align: center;\" width=\"37\">\u2013<\/td>\n<td style=\"text-align: center;\" width=\"42\">(+)<\/td>\n<td style=\"text-align: center;\" width=\"129\">(\u2013) always<\/td>\n<td style=\"text-align: center;\" width=\"121\">Spontaneous<\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;\" width=\"37\">+<\/td>\n<td style=\"text-align: center;\" width=\"42\">+<\/td>\n<td style=\"text-align: center;\" width=\"129\">(+) at low temperature<br \/>\n(\u2013) at high temperature<\/td>\n<td style=\"text-align: center;\" width=\"121\">Non-spontaneous Spontaneous<\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;\" width=\"37\">\u2013<\/td>\n<td style=\"text-align: center;\" width=\"42\">\u2013<\/td>\n<td style=\"text-align: center;\" width=\"129\">(\u2013) at high temperature<br \/>\n(+) at low temperature<\/td>\n<td style=\"text-align: center;\" width=\"121\">Spontaneous Non spontaneous<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3><span class=\"ez-toc-section\" id=\"SECTION-10-THERMOCHEMISTRY\"><\/span>SECTION 10 : THERMOCHEMISTRY<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\"><strong>Thermochemical Standard State :<\/strong> In thermodynamics, standard state of a substance at a specified temperature is its most stable, pure form at 1 bar pressure.<\/p>\n<p style=\"text-align: justify;\">For example, the standard state of liquid water at 300 K is pure liquid water at 300 K and 1 bar. For example, for the combustion of 1 mol of methane under standard conditions, at 298 K we write the equation<\/p>\n<p style=\"text-align: center;\">CH<sub>4<\/sub>(g) + 2O<sub>2<\/sub>(g) \u2192 CH<sub>4<\/sub>(g) + 2H<sub>2<\/sub>O (<em>l<\/em>), \u2206H (298 K) = \u2013890.4 kJ mol<sup>\u20131<\/sup><\/p>\n<p style=\"text-align: justify;\"><strong>Thermochemical Equations :<\/strong> A balanced chemical reaction together with the value of heat (energy)<br \/>\nevolved or absorbed (i.e., value of \u2206H) during reaction is called a <strong>thermochemical equatio<\/strong>n.<\/p>\n<p style=\"text-align: center;\"><strong>Example :<\/strong> C<sub>2<\/sub>H<sub>5<\/sub>OH (<em>l<\/em>) + 3O<sub>2<\/sub> (g) \u2192 2CO<sub>2<\/sub> (g) + 3H<sub>2<\/sub>O (<em>l<\/em>) ; \u2206H = \u20131367 kJ mol<sup>\u20131<\/sup><\/p>\n<p style=\"text-align: justify;\"><strong>Conventions regarding Thermochemical Equations :<\/strong> In writing thermochemical equations, the<br \/>\nfollowing conventions are followed :<\/p>\n<ol>\n<li style=\"text-align: justify;\">For exothermic reaction, \u2206H = \u2013ve and for endothermic reaction, \u2206H = +ve.<\/li>\n<li style=\"text-align: justify;\">The coefficients in a thermo chemical equation refer to the <strong>number of moles<\/strong> of reactants and products involved in the reaction.<\/li>\n<li>When a chemical equation is reversed, the value of <img decoding=\"async\" class=\"alignnone size-full wp-image-1211\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-26.png\" alt=\"NEET Chemistry Class XI\" \/> is reversed in sign. For example<\/li>\n<\/ol>\n<p style=\"text-align: center;\">N<sub>2<\/sub> (g) + O<sub>2<\/sub> (g) \u2192 2NO (g); \u2206H = +180.0 kJ mol<sup>\u20131<\/sup><\/p>\n<p style=\"text-align: center;\">2NO<sub>2<\/sub> (g) \u2192 N<sub>2<\/sub> (g) + O<sub>2<\/sub> (g); \u2206H = \u2013180.0 kJ mol<sup>\u20131<\/sup><\/p>\n<ol style=\"text-align: justify;\" start=\"4\">\n<li style=\"text-align: justify;\">If the coefficients of the substances involved in a reaction are multiplied or divided by certain factor, then the value of \u2206H is also treated in the same way, but unit of \u2206H will remain kJ mol<sup>\u20131<\/sup> . For example,<\/li>\n<\/ol>\n<p style=\"text-align: justify;\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1330 size-full aligncenter\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/thermodynamics.png\" alt=\"thermodynamics\" width=\"417\" height=\"47\" srcset=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/thermodynamics.png 417w, https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/thermodynamics-300x34.png 300w\" sizes=\"auto, (max-width: 417px) 100vw, 417px\" \/><\/p>\n<p style=\"text-align: center;\">2P (s) + 3Br<sub>2<\/sub> (<em>l<\/em>) \u2192 2PBr<sub>3<\/sub> (g); \u2206H = \u2013243.0 kJ mol<sup>\u20131<\/sup><\/p>\n<ol style=\"text-align: justify;\" start=\"5\">\n<li style=\"text-align: justify;\">The physical states of the different reactants and products must be indicated because the value of \u2206H changes with the change in the physical states. For examples ;<\/li>\n<\/ol>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1331 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-27.png\" alt=\"formula\" width=\"405\" height=\"93\" srcset=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-27.png 405w, https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-27-300x69.png 300w\" sizes=\"auto, (max-width: 405px) 100vw, 405px\" \/><\/p>\n<ol style=\"text-align: justify;\" start=\"6\">\n<li style=\"text-align: justify;\">The allotropic form of substances must be indicated because the value of \u2206H also depends upon allotropic form of substances used. For example,<\/li>\n<\/ol>\n<p style=\"text-align: center;\">C (graphite) + O<sub>2<\/sub> (g) \u2192 CO<sub>2<\/sub> (g); \u2206H<sup>\u03b8<\/sup> = \u201394.0 kJ mol<sup>\u20131<\/sup><\/p>\n<p style=\"text-align: center;\">C (diamond) + O<sub>2<\/sub> (g) \u2192 CO<sub>2<\/sub> (g); \u2206H<sup>\u03b8<\/sup> = \u201394.5 kJ mol<sup>\u20131<\/sup><\/p>\n<p><strong>Standard Enthalpy Changes of Reaction :<\/strong> Standard enthalpy of reaction is the enthalpy change for<br \/>\na reaction when all the participating substances (elements and compounds) are in their standard states. It is denoted by symbol<img decoding=\"async\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/changes-of-reaction.png\" \/>.<\/p>\n<p style=\"text-align: justify;\"><strong>Example :<\/strong> The reaction,<\/p>\n<p style=\"text-align: center;\">H<sub>2<\/sub> (g) + Cl<sub>2<\/sub> (g) \u2192 2HCl (g) ; \u2206H = \u201344.0 kcal,<\/p>\n<p style=\"text-align: justify;\">indicates that when 1 mole hydrogen (2 g hydrogen) in its standard state completely reacts with 1 mole chlorine (71 g chlorine) in its standard state to form 2 mole HCl (73 g HCl) in its standard state, the amount of heat evolved is 44.0 kcal or the enthalpy decreases by 44.0 kcal or the reacting system loses 44.0 kcal of heat or the standard enthalpy change of the reaction, i.e.,<\/p>\n<p style=\"text-align: center;\">\u2206H = \u2013 4.0 kcal<\/p>\n<h3><span class=\"ez-toc-section\" id=\"SECTION-11-HESSS-LAW-OF-CONSTANT-HEAT-SUMMATION\"><\/span>SECTION 11 : HESS\u2019S LAW OF CONSTANT HEAT SUMMATION<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">This law states that, <strong>if a reaction is the sum of two or more constituent reactions, then \u2206H (enthalpy change) for the overall process must be sum of the \u2206H\u2019s of the constituent reactions. In other words, the enthalpy change for a reaction is the same whether it occurs in one step or in a series of steps.<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1334 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/hess-law.png\" alt=\"hess law \" width=\"293\" height=\"181\" \/><\/p>\n<p style=\"text-align: justify;\"><strong>Example :<\/strong> Let us consider a chemical change in which \u2018A\u2019 changes into \u2018D\u2019. If this change, A \u2192 D, can take place either in one step or in more than one step as shown in figure.<br \/>\nThen according to Hess\u2019s law, we can write<\/p>\n<p style=\"text-align: center;\">\u2206r H<sup>\u2013<\/sup> = \u2206<sub>1<\/sub>H + \u2206<sub>2<\/sub>H<\/p>\n<p style=\"text-align: justify;\">Hess\u2019s law can be verified experimentally with the help of following examples.<\/p>\n<p style=\"text-align: justify;\"><strong>Formation of CO<sub>2<\/sub> from Carbon<\/strong><\/p>\n<p style=\"text-align: justify;\"><strong>First Method :<\/strong> Carbon is directly converted into CO<sub>2<\/sub> (g)<\/p>\n<p style=\"text-align: center;\">C (s) + O<sub>2<\/sub> (g) \u2192 CO<sub>2<\/sub> (g);\u00a0 \u00a0 \u00a0 \u00a0 \u2206<sub>r<\/sub>H = \u2013393.5 kJ mol<sup>\u20131<\/sup><\/p>\n<p style=\"text-align: justify;\"><strong>Second Method :<\/strong> Carbon is first converted into CO (g) and then CO (g) into CO<sub>2<\/sub> (g), i.e., conversion has been carried in two steps.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1337 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-28.png\" alt=\"formula\" width=\"672\" height=\"153\" srcset=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-28.png 672w, https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/formula-28-300x68.png 300w\" sizes=\"auto, (max-width: 672px) 100vw, 672px\" \/><\/p>\n<p style=\"text-align: justify;\"><strong>Conclusions Drawn from Hess\u2019s Law<\/strong><\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li style=\"text-align: justify;\">Enthalpy change of a reaction (\u2206<sub>r<\/sub>H) is independent of the path followed, i.e., enthalpy is a state function.<\/li>\n<li style=\"text-align: justify;\">\u2206<sub>r<\/sub>H is independent of the time consumed in the process.<\/li>\n<li style=\"text-align: justify;\">Thermochemical equation can be added, subtracted or multiplied like algebraic equations.<\/li>\n<\/ol>\n<p style=\"text-align: justify;\"><strong>Applications of Hess\u2019s Law<\/strong><\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li style=\"text-align: justify;\">The enthalpies of formation of many compounds cannot be determined experimentally. These are calculated by the application of Hess\u2019s law. It can be explained by following example.<\/li>\n<\/ol>\n<p style=\"text-align: justify;\"><strong>Determination of Enthalpies of Slow Reactions like \u2206H of Transition<\/strong><\/p>\n<p style=\"text-align: justify;\">Elements like carbon, sulphur, phosphorus etc., exist in different allotropic form. The enthalpy of transition is the change in enthalpy when one mole of allotropic form of a substance change to the other and vice versa.<\/p>\n<p style=\"text-align: justify;\">The change is very slow and the amount of heat energy exchanged is so small that the value cannot be determined experimentally. However, enthalpies of such transitions can be determined by Hess\u2019s law as explained by following example.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"SECTION-12-BOND-ENERGY-OR-BOND-ENTHALPY\"><\/span>SECTION 12 : BOND ENERGY OR BOND ENTHALPY<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">The amount of energy required to break one mole of bond of a particular type between the atoms in the gaseous state, i.e., to separate the atoms in the gaseous state under 1 atm. pressure and the specified temperature is called bond dissociation energy.<\/p>\n<p style=\"text-align: justify;\"><strong>Example :<\/strong><\/p>\n<p style=\"text-align: center;\">H \u2013 H (g) \u2192 2H (g);\u00a0 \u00a0 \u00a0 \u00a0\u2206H = +433 kJ mole<sup>\u20131<\/sup><\/p>\n<p style=\"text-align: center;\">Cl \u2013 Cl (g) \u2192 2Cl (g);\u00a0 \u00a0 \u00a0 \u2206H = +242.5 kJ mole<sup>\u20131<\/sup><\/p>\n<p style=\"text-align: center;\">H \u2013 Cl (g) \u2192 H(g) + Cl (g); \u2206H = +431 kJ mole\u20131<\/p>\n<p style=\"text-align: justify;\">The bond dissociation energy of a diatomic molecule is called bond energy. When more than one bond of the same kind are present in a compound, then the average bond dissociation energy required to break each bond in a compound is called bond energy.<\/p>\n<p style=\"text-align: justify;\"><strong>Example :<\/strong> Dissociation of H<sub>2<\/sub>O molecule<\/p>\n<p style=\"text-align: center;\">H<sub>2<\/sub>O (g) \u2192 H (g) + OH (g);\u00a0 \u00a0 \u00a0\u2206H = 497.8 kJ mole<sup>\u20131<\/sup><\/p>\n<p style=\"text-align: center;\">OH (g) \u2192 H (g) + O (g);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u2206H = 428.5 kJ mole<sup>\u20131<\/sup><\/p>\n<p style=\"text-align: justify;\">The average bond dissociation energy gives the value of O \u2013 H.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1344 size-full\" src=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/bond-energy.png\" alt=\"bond energy\" width=\"519\" height=\"53\" srcset=\"https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/bond-energy.png 519w, https:\/\/www.meniit.com\/study-material\/wp-content\/uploads\/2024\/08\/bond-energy-300x31.png 300w\" sizes=\"auto, (max-width: 519px) 100vw, 519px\" \/><\/p>\n<p style=\"text-align: justify;\">Application of Bond Energy<\/p>\n<ol>\n<li style=\"text-align: justify;\"><strong>Heat of Reactions :<\/strong> Enthalpy of reaction = \u2211Bond energies of reactants &#8211; \u2211 Bond energies of products<\/li>\n<li style=\"text-align: justify;\"><strong>Determination of Resonance Energy :<\/strong> When a compound shows resonance there is considerable difference between the heat of formation as calculated from bond energies and that determined experimently. Resonance Energy = Experimental or actual heat of formation \u2013 Calculated heat of formation.<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<div class=\"newspaper-x-tags\"><strong>TAGS: <\/strong><span><a href=\"https:\/\/www.meniit.com\/study-material\/tag\/bond-energy\" rel=\"tag\">Bond energy<\/a><\/span><a href=\"https:\/\/www.meniit.com\/study-material\/tag\/bond-enthalpy\" rel=\"tag\">Bond enthalpy<\/a><\/span><a href=\"https:\/\/www.meniit.com\/study-material\/tag\/hesss-law\" rel=\"tag\">Hess&#8217;s law<\/a><\/span><a href=\"https:\/\/www.meniit.com\/study-material\/tag\/second-law-of-themodynamics\" rel=\"tag\">Second law of Themodynamics<\/a><\/span><a href=\"https:\/\/www.meniit.com\/study-material\/tag\/thermochemistry\" rel=\"tag\">Thermochemistry<\/a><\/span><a href=\"https:\/\/www.meniit.com\/study-material\/tag\/thermodynamics\" rel=\"tag\">Thermodynamics<\/a> <\/div>\n","protected":false},"excerpt":{"rendered":"<p>SECTION 1 : SOME BASIC TERMS OF THERMODYNAMICS System : A system is defined as that part of the universe&nbsp;&nbsp;&#8230;.<a class=\"read_more\" href=\"https:\/\/www.meniit.com\/study-material\/neet\/class-11th\/chemistry\/thermodynamic\" rel=\"nofollow\">Read More >><\/a><\/p>\n","protected":false},"author":5,"featured_media":1587,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"om_disable_all_campaigns":false,"rank_math_lock_modified_date":false,"footnotes":""},"categories":[268,241,240],"tags":[450,451,449,447,448,446],"class_list":["post-1283","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-chemistry","category-class-11th","category-neet","tag-bond-energy","tag-bond-enthalpy","tag-hesss-law","tag-second-law-of-themodynamics","tag-thermochemistry","tag-thermodynamics"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/posts\/1283","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/comments?post=1283"}],"version-history":[{"count":13,"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/posts\/1283\/revisions"}],"predecessor-version":[{"id":1466,"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/posts\/1283\/revisions\/1466"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/media\/1587"}],"wp:attachment":[{"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/media?parent=1283"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/categories?post=1283"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.meniit.com\/study-material\/wp-json\/wp\/v2\/tags?post=1283"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}