02b First Law concepts.ppt

1、Lectures: M14:30-16:10AM, H101,Course Information,Instructor: Jianping Liu,email: ,Office Hours: Fri 16:00-17:30 H219,Mobile:Bilingual Course by Jianping Liu,F10:00-11:40AM, 8110,Atkins & de Paula: Atkins Physical Chemistry 7e,2,The first law: the concepts,Bilingual Course by Jianping L

2、iu,2.4 Heat transactions, internal energy change and heat transfer,In general,dU = dq + dwexp+ dwe,dU = dqv,at constant volume (dwexp = 0) and no additional work (dwe = 0),U = qv,(a) Calorimetry,the study of heat transfer during physical and chemical processes, Adiabatic bomb calorimeter,The common

3、device for measuring U.,qV = CT,U = qv,( C is the calorimeter constant),(b) Heat capacity at constant volume CV,Since dU = dqv then,the internal energy varies with the temperature and the volume being held constant., internal energy change at constant volume,(b) Heat capacity at constant volume CV,

4、Why introduce?,2.5 Enthalpy H,In general, the system is free to change its volume, then,can q equal to another thermodynamic property of the system at constant pressure?,Question:,(a) The definition of enthalpy,(state function), enthalpy change,Infinitesimal,measurable,2.5 Enthalpy H,(at equilibrium

5、 and expansion work only),at constant pressure,Infinitesimal,measurable,for a reaction that produces or consumes gas,for a perfect gas,Since dH = dqp then, heat capacity at constant pressure Cp,Questions:, Cp CV?, Cp = f(T)?,The variation of capacity with temperature,Two empirical expressions, The m

6、olar constant-volume heat capacity,(d) relation between heat capacities,monatomic gas,diatomic gas, for a perfect gas,体积功,等容无其它功,等压无其它功,显热,求 W, q , U , H。,q=0 (adiabatic),附2.2 1 mol 理想气体简变 (迅速膨胀),q=0 (绝热),U = q + w = -1030J,求 W, q , U , H。,附2.2 1 mol 理想气体简变 (迅速膨胀),1.0 mol 乙醇在正常沸点下蒸发成乙醇气体,求 此过程 W, Q

7、, U , H。,附2.3 等温等压下相变,附2.3 等温等压下相变,解(1) ：,Q1= -110.52 kJ.mol-1,U1=Q1+W1= -111.76 kJ mol-1,H1=Qp=Q1= -110.52 kJ.mol-1,解(2) ：,Q2= U2 -W2,U2= U1= -111.76 kJ mol-1,H2= H1= -110.52 kJ.mol-1,=(-111.76)-(-61.39)=-56.37 kJ.mol-1,Summary,Total differential of Z,z depends only on the initial and final state,a

8、nd is independent of the path.,Numerical problems,P2.3 at page 69,P2.3,Numerical problems,P2.3 at page 69,P2.3,( isotherm ),Numerical problems,P2.3 at page 69,Numerical problems,P2.3 at page 69,Numerical problems,P2.3 at page 69,P2.3, Adiabatic,for perfect gas,2.6 Adiabatic changes,(1) The work of a

9、diabatic change,Decide the initial and final state,2.6 Adiabatic changes, the state function,The state function and the process function, isothermal process, adiabatic process, the adiabatic reversible expansion,perfect gas,adiabatic,reversible,2.6 Adiabatic changes,The adiabatic reversible expansion,Illustration 2.5,(2) Heat capacity ratio,2.6 Adiabatic changes, isothermal, adiabatic,Atkins & de Paula: Atkins Ph