Question

Heat of combustion of ethanol at constant pressure and at temperature TK is found to be `-q J" mol"^(-1)`. Hence, heat of combustion (in J `mol^(-1)`) of ethanol at the same temperature and at constant volume will be :
A. RT - q
B. `-(q+RT)`
C. q - RT
D. q + RT

Answer 1

Correct Answer - A
`C_(2)H_(5)OH(l)+3O_(2)(g)rarr2CO_(2)(g)+3H_(2)O(l)`
`Deltan_(g)=2-3=-1`
`DeltaH=DeltaU+Deltan_(g)RT`
`DeltaU=DeltaH+RT=RT-q`