Physical Chemistry Chapter 2 Heat Two bodies at unequal temperatures are placed in contact m,C2,12 (72>71) T12 m2c2(72-T7)=m;(Tr-71)=q (2.34) Specific heat capacity
12 Two bodies at unequal temperatures are placed in contact m1 , c1 , T1 m2 , c2 , T2 (T2>T1 ) Tf m2 c2 (T2 −Tf ) = m1 c1 (Tf −T1 ) q (2.34) Specific heat capacity Heat Physical Chemistry Chapter 2 T1<Tf<T2
Physical Chemistry Chapter 2 Heat -n, (2.34) dqp = mcpdT 2.35) p=m Cp(t)dT closed syst, P const.(2.36) P (2.37 72 m2L Cp (r)dT=m,l CP (T)dT=qp 2.38) 13
13 dqP mcP dT (2.35) Heat closed syst., P const. = 2 1 ( ) T T qP m CP T dT (2.36) dT dq C P P = (2.37) = = 2 1 2 1 ( ) ( ) 2 1 T T T T P P P f f m c T dT m c T dT q (2.38) m2 c2 (T2 −Tf ) = m1 c1 (Tf −T1 ) q (2.34) Physical Chemistry Chapter 2
Physical Chemistry Chapter 2 The First law of Thermodynamics The total energy of an isolated thermodynamic system is constant the conservation of energy Energy cannot be created or destroyed 40=9+w (241) Closed system at rest in the absence of external fields q is the heat supplied to the system w is the work done on the system AU is the internal energy of the system
14 The total energy of an isolated thermodynamic system is constant the conservation of energy The First Law of Thermodynamics Energy cannot be created or destroyed Closed system at rest in the absence of external fields U = q + w (2.41)* q is the heat supplied to the system w is the work done on the system U is the internal energy of the system Physical Chemistry Chapter 2
Physical Chemistry Chapter 2 - Heat and work Both are measures of energy transfer, and both have the same units as energy The unit of heat can be defined in terms of oule 1cal=4.184J (244) The calorie defined by(2.44)is called thermodynamical calorie, cali 15
15 Heat and Work 1 cal 4.184 J (2.44)* The calorie defined by (2.44) is called thermodynamical calorie, calth Both are measures of energy transfer, and both have the same units as energy. The unit of heat can be defined in terms of joule. Physical Chemistry Chapter 2
Physical Chemistry Chapter 2 ≡: Enthalpy H≡U+Pp (245) Since u p vare state functions, h is a state function Let qp be the heat adsorbed in a constant-pressure process in a closed system, from the first law △U=U2-U1=q+=q r Pdv pl dv=p-P(2-K) p=0+PV-U-PY P,=P2,=P (U2+PV2)(1+PV1)=H2-H1 AH-qp at cons P, closed syst. P-V work only(2.46)
16 Enthalpy H U + PV (2.45)* qP =U2 + PV2 −U1 − PV1 Let qP be the heat adsorbed in a constant-pressure process in a closed system, from the first law = − = + = − 2 1 2 1 V V U U U q w q PdV = − = − − 2 1 ( ) 2 1 V V qp P dV qP P V V 2 2 2 1 1 1 2 1 = (U + PV )−(U + PV ) = H − H H = qP at cons P,closed syst. P-V work only (2.46) Since U, P, V are state functions, H is a state function. P1=P2=P Physical Chemistry Chapter 2