Question

the enthalpy of combustion of CH4(g) to make H2O(l) and CO2(g) is -2340 kJ mol-1. The enthalpy of combustion of CH2(g) to make H2O(l) and CO2(g) is -2760 kJ mol-1. The enthalpy of formation of H2O(l) is -286 kJ mol-1. All the data are for 298 K. The heat capacities for O2(g), CHA(8), CH3(g), H2O(l) and CO2(8) are 29, 61, 71, 75 and 37 JK"mor", respectively. Deduce a) 4U298 for the combustion of C4H8(g). 5) AH for the combustion of C4H8(8) at 900 K. AH298 for the reaction CH4(g) + 2 H2(g) - C4H3(g). 3) De po punon edou OSIS:

Answer 1

Solution:

The enthalpy of combustions and heat capacities are given

Answen Given: enthalpy rembutien C H) to make o l) and cais-23yo KJmel Enthalpy o cenbustien q Cytte (to nake 0e) and cois-2#60kJmiol The onthalay 9 formatien g ol4) is 286 kmet Tue Aeat capacities CR a) Cty( H), H20(l) and co) aue 29,6)) 775 and37 JKm respetively Hene Tue egnations ane CoM Y AcH=-2340 kJmol 4C )+ 4 HO () 4D 60g) CytHs CA) AcH=-2760k Jmal 2 H2Ol) 4fH = -286 KTmd - 2H2a)+ 0lg) nodhodee'y S 379971 AH= 6Ut4T (a) 40 fon combultion Cy He AH-2760KJmor R=&.314 X10kmol K T298K A Jaon equation Ae E2760)-(-3)&.g14 Ml 073X 298 = -2360 +3 x8.34 X103X298 lA = -2760+ 7.4 32 A2 AU 252 KImol E $ 298

(b) AcH at 40ok for CyHg Ca) AH(900K)AH (298k)+ACp 4T AT= 90-298 = 602 K Cp Cy He Cg)= 71 JKme p )-75 JKnet cp O3 C9)=29 JmelpCo37 JKnol HODK)- AH(298k)+ ACPAT ck)2760xo 3)+x15+yx37)-+6x29) AMAcokC-260X103) + [300tly8-717) X602 = C-2760X103)+7448-245)x602 = -2760X/03 203X602 - -2760X/o 3 + 122206 = -2637794J mol x (9-298) 1 (10s lsg AH(9k 263 7. 79y kJmor Henee enthalpy embuatiou CyHa () at 90ok 2631.79Uy&kInt V e) Entaleyrectien Cyty +2l9)te) y Hul+ 4/0) +220(0,42 OKTh CyHal9)+ bo, 4C09)o) A260k Add eg uDand aud substrect egu DyH= AyH-2340-a2 86+2160

Ag(-23y0-2X286)+ 2160 45H-158 KJmal Enthalpy reaction yAy Ca)+2H2(g)-34Hl) aund to be - 158kimal