Heat Capacity (C) : 1 K ( 1 oC)

(s) : 1 (Specific heat) 1 K

1. : Cv = DqV = dUdTdT

2. : CP= DqP = dHdTdT

0.28 100 oC 180 oC

: Cp = a + bT + CT 2 + ...Cp(N2 ,g) = 27.3 + 5.23x10-3 T - 0.04x10-7 T2 +... J K-1 mol-1

T2 T2 DH = CpdT = n CpdT T1 T1= n Cp(T2-T1)T1 = 100 OC = 373 KT2 = 180 OC = 453 K

DH = (0.01mol) (27.3 + 5.23x10-3 T - 0.04x10-7 T2) dT453373= (0.01) [2184 + 172.8 - 0.055] = 23.57 J

Cp Cv enthalpy : H = U + PV dH = dU + d (PV)

U = 3 RT monoatomic ideal gas n = 12

heat capacity ratio = CP = 5 = 1.66CV3(g)

Cp > Cv

?

CP

CP = CV + (-W) = CV + Pext DV Dn = 1; DT = 1;

(Thermochemistry)

H2S(g) + (3/2)0 2(g) H2O(l) + SO2(g) DHo298 = - 561 KJ (Thermochemical reaction)

DH, DHreactionSTP = Standard Temperature and Pressure P = 1 atm ; T = 273.15 K (0 OC)

H2S(g) + (3/2)0 2(g) H2O(l) + SO2(g) DHO298 = - 561 KJni nj

DH > O : (Endothermic reaction)DH < O : (Exothermic reaction) DH

absolute enthalpy (H) DH ?

1) Hess Law2) Bond Energy3) Heat of Formation (Hess Law) The Law of Constant Heat Summation DH ?

???

H2(g) + 1 O2 (g) H2O(g) DH o291.75 = - 241.75 kJ

1. DH

2. DH 2 H2O(g) 2H2(g) + O2(g) DH o291.15 = 483.50 kJ

Ex 298 KC2H4(g) + H2(g) C2H6(g)1) C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(l) DH o= -1411.26 kJ2) 2H2(g) + O2(g) 2H2O(l) DH o = -571.68 kJ1233) C2H6(g) + 7 O2(g) 3H2O(l) + 2CO2(g) DH o = -1559.80 kJ2

2(4) = (2) C2H4(g) + H2(g) C2H6(g) DH

(1)+ (4) - (3) : DH o = DH o + DH o - DH o = - 137.3 kJ 143= -1411.26 - 285.84 - (-1559.8)

Bond Energy (Bond Enthalpy)A -- B A + B DH = . kJ mol-1

1. (Dissociation bond enthalply)CH4 CH3 + H CH3 CH2 + HCH2 CH + HCH C + HDH o298 = 422 kJDH o298 = 364 kJDH o298 = 385 kJDH o298 = 335 kJ

2. (Average bond enthalpy)

C H C + HDH o298 = 413 kJC C C + CDH o298 = 348 kJC C C + CDH o298 = 614 kJC C C + CDH o298 = 839 kJAverage bond enthalpy

Table : Selected values of mean bonddissociated energies, DH(x-y) in kJ mol-1

DH 1. (reactants) ()

2. () (products) DH

- () - ()

Ex. DHo CH3OH(g) + HBr(g) H2O(g) + CH3Br(g)3 C - H = 3(412) = 1236 kJ 3C - H = 3(- 412) = - 1236 kJ C - O = 360 C - Br = - 285 O - H = 463 O - H = - 463 H - Br = 366 O - H = - 463 2425 kJ - 2447 kJ DHo = (-2447) + (2425) = -22 kJ