Question

Determine `Delta U^(@) ` at 300K for the following reaction using the listed enthalpies of reaction :
`4CO(g)+8H_(2)(g)to3CH_(4)(g)+CO_(2)(g)+2H_(2)O(l)`
`C("graphite")+(1)/(2)O_(2)(g)to CO(g), DeltaH_(1)^(@)=-110.5KJ`
` CO(g)(1)/(2)O_(2)(g)toCO_(2)(g), DeltaH_(2)^(@)=-282.9KJ`
`H_(2)(g)+(1)/(2)O_(2)(g)to H_(2)O(l), DeltaH_(3)^(@)=-285.8KJ`
`C("graphite")+2H_(2)(g)to CH_(4)(g), DeltaH_(4)^(@)=-74.8KJ`
A. `-653.5` kJ
B. `-686.2` kKJ
C. `-747.4` kJ
D. None of these

Answer 1

Correct Answer - D
`DeltaH^(@)=-3DeltaH_(1)^(@)+DeltaH_(2)^(@)+2DeltaH_(3)^(@)+3DeltaH_(4)^(@)`
`=-747.4kJ`
`DeltaH^(@)=DeltaU^(@)+Deltan_(g)RT," where " Deltan_(g)=-8`
`-747.4=DeltaU^(@)=(8xx8.314xx300)/(1000)`
`DeltaU^(@)=-727.44kJ`