武汉大学：《物理化学 Physical Chemistry》课程教学资源（PPT课件讲稿）03 热化学（ThermoChemistry）

热力学第一定律 热化学( ThermoChemistry) 1.吸热反应&放热反应 2标准态:指定温度(通常是29815K),一个标准大气压 标准焓变ΔH°变化前后物质都处于标准态 3.热化学方程式:注明状态 标准摩尔焓变AHn;标准反应焓变ΔrH° CH4g)+2o2(9) Co2 (g)+2H2 O() 4, Ho=-890 kJ mol △rH°=2△Hm°(H2O)+△Hn(CO2)-△Hn。(CH4)-2△Hn(O2)

热化学 (ThermoChemistry) 1. 吸热反应 & 放热反应 2. 标准态: 指定温度(通常是298.15K), 一个标准大气压. 标准焓变 H: 变化前后物质都处于标准态. 3. 热化学方程式: 注明状态 标准摩尔焓变 Hm ; 标准反应焓变rH rH = 2 Hm (H2O) + Hm (CO2 ) - Hm (CH4 ) - 2 Hm (O2 ) 热力学第一定律

热力学第一定律 盖斯定律( Hess law) The standard enthalpy of an overall reaction is the sum of the standard enthalpies of the individual reactions into which the overall reaction may be divided -Individual steps may not be"real" reactions, but must balance △/kJmo C3H6(g)+H2(g) C3Ha(g) 124 C3H8(g)+502(g)3CO2(g)+4H2O() 2220 H2O() H2(g)+O2(g) +286 C3H6(g)+(9/2)O2(g) 3cO2(g)+3H2O() 2058

盖斯定律 (Hess’ Law) 热力学第一定律

热力学第一定律 标准摩尔生成焓 standard enthalpy of formation,△HP° 反应焓:标准态的稳定单质→标准态的某物质 6C(s, graphite)+ 3H2 - ChOo elements △H=+49.0kJmo ∑w1H°-∑ reactants products reactants △H products

标准摩尔生成焓 反应焓: 标准态的稳定单质 →标准态的某物质 热力学第一定律

热力学第一定律 Group Contributions Sometimes it is difficult to exactly thermodynamically break enthalpies of formation down into contributions from individual atoms and bonds mean bond enthalpies,△H(A-B)平均键焓 enthalpy change associated with breaking of a specific bond, A-B A-B(g) A(g)+ b(g) △H(A-B) This is an unreliable method, since AH(A-B )are average values for series of unrelated compounds(different geometries, isomers, etc. thermochemical groups atom or physical group of atoms bound to at least two other atoms enthalpy of formation is associated with sum of contributions associated with all of the thermochemical groups into which the molecule can be divided-sometimes called Benson thermochemical groups

平均键焓 热力学第一定律

热力学第一定律 Benson Group Contributions Group △HP/kJmo1Cpm°JK1mo C(H)2C)-42.17 259 C(H)2C)2-20.7 22.8 C(H)C3 -6.19 18.7 C(C) +8.16 18.2 Example C(C)4 C(H)2C)2 Estimate standard enthalpy of formation for hexane(g& I)at 298 K Decomposition: two C(H)3(C) groups and four C(H)2(C)2 groups △H(C。H1429) 2(-42.17)+4(-20.7 =-167.1kJmo1 △a(CH14)=289kJmo1 △H(CAH 167.1-289 196.0 kJ mol- Experimental:-1987 kJ mol

热力学第一定律

热力学第一定律 反应焓与温度的关系(基尔霍夫定律 Kirchoff's law) Products H(T2)=H(1)+|C,d7 工 △H°(T Reactants △,H"(T2)=△H(T)+(△Cam Temperature, T m ∑vCaJ products reactants

反应焓与温度的关系 (基尔霍夫定律 Kirchoff’s Law) 热力学第一定律

热力学第二定律 Perfectly elastic ball; Vacuum Real world Ball Egg P.E PE○ PE KE KE Heat The First Law Fulfilled! Ist Law: Where does the energy go? Broken egg: Disorganized form of matter

Perfectly elastic ball; Vacuum The First Law Fulfilled! Real World 1st Law: Where does the energy go? Broken egg: Disorganized form of matter. 热力学第二定律

热力学第二定律 (1)规则运动→无规则运动(混乱度增大么y The universe tends towards more random disorganized states (2)自发性(方向性)

(1) 规则运动 → 无规则运动 (混乱度增大!) (2) 自发性 (方向性) 热力学第二定律 impossi ble

热力学第二定律 Hot source T H t source Heat Flow of +20 energy +5 -15 Engine Work T 第二类动机 Cold sink 2. Lord Kelvin(1824-1907)In a cycle of processes, it is impossible to transfer heat from a heat reservoir and convert it all into work without at the same time transferring a certain amount of heat from a hotter to a colder body The Second Law

第二类永动机 The Second Law 热力学第二定律

热力学第二定律 熵的定义 Second law Uses entropy, S, to identify the spontaneous(irreversible) changes among the permissible changes Entropy is a measure of molecular disorder in a system, letting us assess whether one state is accessible from another via spontaneous change 需设计 w:有序,对S无贡献 熵的表达式 Why g, not w? rev △S re\ infinitessimal change measurable change

熵的表达式 熵的定义 Why q, not w? 热力学第二定律 需设计 w: 有序, 对S无贡献