8 Thermo-Chemistry & Chemical Equilibrium Objective Thermo-effect in chemical reaction and evaluation of reaction heat Theoretical adiabatic combustion temperature Chemical equilibrium and equilibrium constant Judgment on direction and limitation of chemical reaction Evaluation on equilibrium constant and dissociation

8.1 1 st Law Analysis of Chemical Reaction Internal Energy and Enthalpy Internal Energy Physical Chemical Potential Kinetic Depends on components Irreverent to temperature

8.1 1 st Law Analysis of Chemical Reaction Work of Chemical Reaction Work Volumetric Work Non-volumetric Work Example: Electricity by Fuel Cell

8.1 1 st Law Analysis of Chemical Reaction Heat of Chemical Reaction Definition: The heat transferred between system and surroundings during chemical reaction. Q > 0: heat transfer to the system Q < 0: heat transfer from the system Q = 0: adiabatic

8.1 1 st Law Analysis of Chemical Reaction st Law of Chemical Reaction Product React

8.2 Thermo-effect of Chemical Reaction Thermo-effect of chemical reaction Constant VolumeConstant Pressure 定容热效应等于 系统内能的变化 定压热效应等于 系统焓的变化 Reaction Heat under and

8.2.1 Thermo-effect at Constant Volume and Pressure Same react Const. P & T Const. V & T Same Product For Ideal Gas n － gas moles

8.2.2 Hess Law Hess ( Russian ) Law The thermo-effect of chemical reaction only depends on the initial and ending state of reaction and is unrelated with reaction path. It is important that different reactions can be related through Hess Law.

8.2.2 Hess Law Example: (1) (2) (1) － (2) NOTICE: Hess Law must be applied to the same reaction.

8.2.3 Temperature Effect Standard Thermo-effect The thermo-effect at Pa and 25 ℃. Two ways: 1. React － Product at T 2 2. React T 2 —T 1 React － Product at T 1 Product T 1 —T 2

8.2.3 Temperature Effect Kirchhoff Equation 化学反应的热效应随温度变化，是由于生成物和反应物的 物理焓随温度变化而引起的。 Physical enthalpy

8.2.3 Temperature Effect Generally, the standard thermo-effect is known The thermo-effect at any temperature

8.3 Combustion Heat & Production Heat Fuel +combustion supporting gases = products + heat Oxygen Air Theoretical oxygen quantity: according to reaction equation Theoretical air quantity=4.76× theoretical oxygen quantity In practical combustions, the air is always excessive

8.3 Combustion Heat & Production Heat Combustion Heat & Thermo-effect of Reaction Combustion Enthalpy: The thermo-effect of 1 mole fuel during complete combustion at standard condition. Its absolute value is heat value. means: Gas: Low Heat Value Liquid: High Heat Value

Total enthalpy of react and product Molar enthalpy at standard condition at standard condition at any temperature, the molar enthalpy: thermo-effect of chemical reaction:

8.3.2 Combustion Heat & Thermo-effect of Reaction Example: Propane Decomposition (1) (2) (3) (1) － (2) － (3)

8.3.3 Production Heat & Thermo-effect of Reaction Total enthalpy of react and product Molar enthalpy at standard condition The enthalpy of simple substance at standard condition is zero. Standard Production Enthalpy of Compound The thermo-effect of 1mol compound produced by stable simple substance at standard condition.

8.3.3 Production Heat & Thermo-effect of Reaction at standard condition at any temperature, the molar enthalpy: at any temperature, thermo-effect of chemical reaction: NOTICE: phase change

8.4 Flame Temperature Adiabatic Combustion: The heat generated by combustion reaction is totally used to raise the temperature of products. Theoretical Flame Temperature: The highest temperature of adiabatic combustion. at constant pressure at constant volume

8.4.1 Theoretical Flame Temperature at Constant Pressure 1st Law

8.4.2 Theoretical Flame Temperature at Constant Volume

8.5 Chemical Equilibrium 2 nd Law of Thermodynamics: Chemical Reaction at Constant Pressure & and Temperature Request of Chemical Equilibrium Chemical Equilibrium: The state that the concentrations of reactants and products is not changed with time.

8.5.1 Request for Chemical Equilibrium At constant pressure and temperature, system is still balanced, so… 即,即, Stoichiometric Coefficient Chemical Potential Partial pressure

8.5.2 Chemical Equilibrium Constant The chemical potential equation is applied to react (A,B) and product (D,E). Their pressure is

8.5.2 Chemical Equilibrium Constant Standard-state Free Enthalpy Change f(T) For given reaction at constant temperature Chemical Equilibrium Constant 化学平衡常数

8.5.2 Chemical Equilibrium Constant indicates the numerical relationship between react and product in system when equilibrium. In handbook 1.Single phase 2.All the components are gas.

8.5.2 Chemical Equilibrium Constant If multi-phases and solid or liquid exists: Because the saturated vapor pressure of solid or liquid is not change and has no relation with its quantity. So… Constant 有多聚相的多相反应的平衡常数由参加反应的气态物质的分 压确定。

8.5.2 Chemical Equilibrium Constant Chemical Equilibrium Constant － Concentration

Chemical Equilibrium Constant － Relative Molar Number Chemical Equilibrium Constant f(T,p)

8.5.2 Chemical Equilibrium Constant Remarks on Chemical Equilibrium Constant ① The of a reaction depends on the temperature only. Example: at specific temperature the following four reactions have same value

8.5.2 Chemical Equilibrium Constant ② is independent of the pressure of the equilibrium mixture. ③ K p is relevant to the form of reaction equation, when the stoichiometric coefficients are doubled, the value of K p is squared.

8.5.2 Chemical Equilibrium Constant ⑤ Evaluation of complex reaction through simple ones. ④ The larger the K p, the more complete the reaction.

8.5.3 Evaluation of Equilibrium Composition Reaction Equation Composition of Product Equilibrium Constant Equilibrium Composition Following Steps: ① Reaction Equation ② Mass Equilibrium Equation ③ Equilibrium Constant ④ Solution to Equilibrium Composition

8.5.3 Evaluation of Equilibrium Composition Example 8-3: 400 ℃, 30.4MPa Init. Mol React Mol Equi. Mol 130 x3x2x 1-x3(1-x)2x Tot. Mol

8.6 Direction & Limits of Chemical Reaction any pressure at constant temperature and pressure for ideal gas 压力商

8.6 Direction & Limits of Chemical Reaction Spontaneously positive reaction Spontaneously reverse reaction Equilibrium State

8.7 Variation of Chemical Equilibrium Temperature for reactant and product

at MPa and constant temperature Vant’Hoff Equation Enthalpy only depends on temperature for ideal-gas: 8.7 Variation of Chemical Equilibrium

for endothermic reaction or for exothermic reaction or 8.7 Variation of Chemical Equilibrium

压力增大，可以使摩尔数减少的反应进行得更完全一些。 压力增大，可以使摩尔数增加的反应进行得更不完全一些。 8.7 Variation of Chemical Equilibrium pressure

惰性气体的影响可以这样理解：在总压不变的 条件下，增加惰性气体的量实际上起到了稀释的 作用，因此它和减少反应系统总压的效应是一样 的。 8.7 Variation of Chemical Equilibrium Inert gases

如果把决定化学平衡的因素加以改变，则化学反应重新开始，新 的化学平衡向着抵消或削弱这种因素的改变的方向移动。这个定律称 为平衡移动定律，或吕 · 查德里原理。 增高（或降低）温度，则反应向吸热（或放热）的方向进行； 增加（或减小）压力，则反应向摩尔数减小（或增大）的方向进行； 增加（或减小）反应物的浓度，则反应正向（或逆向）进行； 增加（或减小）生成物的浓度，则反应逆向（或正向）进行； 增加（或减小）惰性气体的量，则反应向体积增大（或减小）的方 向进行。 8.7 Variation of Chemical Equilibrium summary

The enthalpy of simple substance at standard condition is zero. Standard Production Free Enthalpy of Compound The free Enthalpy difference of 1mol compound produced by stable simple substance at standard condition. 8.8 Evaluation of Equilibrium Constant For ideal gas reactions Based on Standard Production Free Enthalpy

Example: 试用标准生成自由焓的数据，求出 25 ℃时的平衡常数 已知反应 8.8 Evaluation of Equilibrium Constant

8.8.1 Based on the third law of thermodynamics The third law of thermodynamics The entropy of any perfect crystal is zero. Standard entropy: 8.8 Evaluation of Equilibrium Constant

8.9 Reversible process of chemical reaction Reversible process and reversible reaction Reversible process : the reverse process could be performed so that the system and surroundings can be restored to their initial states with no change in the system or surroundings. Ex. storage battery Reversible reaction : the reverse reaction could be performed.

8.9.2 Max. Non-expansion Work At constant temperature & volume Free Energy of Reactant and Product 8.9 Reversible process of chemical reaction

At constant temperature & pressure Free Enthalpy of React and Product 8.9 Reversible process of chemical reaction

8.10 Dissociation & Its Degree 离解 (Dissociation) 是指化合物（或反应生成物）分解成为 一些较为简单的物质与元素。 离解度 (Degree of Dissociation, ) 是指达到化学平衡时, 物质离解了的百分数。 离解度随着温度和压力的变化符合平衡移动原理。