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所在平台: Udemy |
课程主页: https://www.udemy.com/course/physical-chemistry-chemical-thermodynamics/
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本课程“物理化学 - 化学热力学”旨在深入探讨化学和物理过程中能量的变化。课程将引导学习者理解热力学基本概念，包括系统与环境的划分、热量（q）与功（w）的交换，以及它们与内能变化（∆U）的关系（∆U = q + w）。 课程强调了状态函数（如内能）和路径函数的区别，并介绍了热量和功的正负号约定。学习者将了解热容（C）的概念，以及热量传递为何会导致温度变化（q = C∆T）。此外，课程还将讲解气体膨胀做功的计算，特别是在可逆过程下的功（w_rev = -p dV），并会涉及理想气体状态方程（pV = nRT）。 在恒容过程下，内能变化等于热量传递（∆U = qV）。然而，化学反应研究中更常遇到的是恒压过程，因此课程引入了另一个重要的状态函数——焓。焓变（∆H）可以从恒压下的热量变化直接获得（∆H = qp），并给出了焓变与内能变化的关联（∆H = ∆U + ∆ngRT）。 课程还会介绍各种焓变，如相变焓（熔化、汽化、升华）以及通过赫斯定律计算生成的焓、燃烧焓等。 第一定律只能描述能量转化，但无法预测反应方向。为此，课程引入了熵（S）的概念，将其定义为衡量无序度的状态函数。对于孤立系统，若发生自发过程，其总熵变（∆S）为正。课程还将介绍熵变的计算方法，特别是对于可逆过程（∆S = q_rev/T），并指出熵变是路径无关的。 课程还包含一系列问题，旨在巩固学习效果，涵盖了热力学状态函数、绝热过程、标准状态下元素的焓、焓变计算、吉布斯自由能与自发性判断（结合焓变和熵变）、内能变化计算、热容相关计算、燃烧热应用、由生成焓计算反应焓、以及判断反应焓变和熵变符号等。 总而言之，本课程为学习者提供了扎实的化学热力学理论基础，并通过实际计算和问题演练，使其能够定量分析和预测化学及物理过程的能量变化和自发性。
SUMMARYThermodynamics deals with energy changes in chemical or physical processes and enables us to study these changes quantitatively and to make useful predictions. For these purposes, we divide the universe into the system and the surroundings. Chemical or physical processes lead to evolution or absorption of heat (q), part of which may be converted into work (w). These quantities are related through the first law of thermodynamics via ∆U = q + w. ∆U, change in internal energy, depends on initial and final states only and is a state function, whereas q and w depend on the path and are not the state functions. We follow sign conventions of q and w by giving the positive sign to these quantities when these are added to the system. We can measure the transfer of heat from one system to another which causes the change in temperature. The magnitude of rise in temperature depends on the heat capacity (C) of a substance. Therefore, heat absorbed or evolved is q = C∆T. Work can be measured by w = -pex ∆V, in case of expansion of gases. Under reversible process, we can put pex = p for infinitesimal changes in the volume making wrev = - p dV. In this condition, we can use gas equation, pV = nRT.At constant volume, w = 0, then ∆U = qV , heat transfer at constant volume. But in study of chemical reactions, we usually have constant pressure. We define another state function enthalpy. Enthalpy change, ∆H = ∆U + ∆ngRT, can be found directly from the heat changes at constant pressure, ∆H = qp.There are varieties of enthalpy changes. Changes of phase such as melting, vaporization and sublimation usually occur at constant temperature and can be characterized by enthalpy changes which are always positive. Enthalpy of formation, combustion and other enthalpy changes can be calculated using Hess's law.First law of thermodynamics does not guide us about the direction of chemical reactions i.e., what is the driving force of a chemical reaction. For isolated systems, ∆U = 0. We define another state function, S, entropy for this purpose. Entropy is a measure of disorder or randomness. For a spontaneous change, total entropy change is positive. Therefore, for an isolated system, ∆U = 0, ∆S > 0, so entropy change distinguishes a spontaneous change, while energy change does not. Entropy changes can be measured by the equation ∆S = qrev/T for a reversible process. qrev/T is independent of path.1 Choose the correct answer. A thermodynamic state function is a quantity (i) used to determine heat changes (ii) whose value is independent of path (iii) used to determine pressure volume work (iv) whose value depends on temperature only. 2 For the process to occur under adiabatic conditions, the correct condition is: (i) ∆T = 0 (ii) ∆p = 0 (iii) q = 0 (iv) w = 0 3 The enthalpies of all elements in their standard states are: (i) unity (ii) zero (iii) < 0 (iv) different for each element 4 The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are, -890.3 kJ mol-1 -393.5 kJ mol-1, and -285.8 kJ mol-1 respectively. Enthalpy of formation of CH4 (g) will be (i) -74.8 kJ mol-1 (ii) -52.27 kJ mol-1 (iii) +74.8 kJ mol-1 (iv) +52.26 kJ mol-1. 5 A reaction, A + B → C + D + q is found to have a positive entropy change. The reaction will be (i) possible at high temperature (ii) possible only at low temperature (iii) not possible at any temperature (v) possible at any temperature 6 In a process, 701 J of heat is absorbed by a system and 394 J of work is done by the system. What is the change in internal energy for the process? 7 Calculate the number of kJ of heat necessary to raise the temperature of 60.0 g of aluminium from 35°C to 55°C. Molar heat capacity of Al is 24 J mol-1 K-1. 8 Enthalpy of combustion of carbon to CO2 is -393.5 kJ mol-1. Calculate the heat released upon formation of 35.2 g of CO2 from carbon and dioxygen gas. 9 Enthalpies of formation of CO(g), CO2 (g), N2O(g) and N2O4 (g) are -110, - 393, 81 and 9.7 kJ mol-1 respectively. Find the value of ∆rH for the reaction: N2O4 (g) + 3CO(g) → N2O(g) + 3CO2 (g) 10 For an isolated system, ∆U = 0, what will be ∆S ?11 For the reaction at 298 K, 2A + B → C ∆H = 400 kJ mol-1 and ∆S = 0.2 kJ K-1 mol-1 At what temperature will the reaction become spontaneous considering ∆H and ∆S to be constant over the temperature range. 12 For the reaction, 2 Cl(g) → Cl2 (g), what are the signs of ∆H and ∆S ?
