Question

The standard enthalpy of formation of octane `(C_(8)H_(18))` is `-250kJ //mol`. Calculate the enthalpy of combustion of `C_(8)H_(18)`. The enthalpy of `CO_(2)(g)` and `H_(2)O(l)` are `-394 kJ//mol` and `-286kJ//mol` respectively.
A. `-5200kJ//mol`
B. `-5726kJ//mol`
C. `-5476kJ//mol`
D. `-5310kJ//mol`

Answer 1

Correct Answer - 3
`C_(5)H_(18)(g)+(25)/(2)O_(2)(g)rarr8CO_(2)(g)+9H_(2)O(l)`
`Delta_(r)H^(@)=8xx(-394)+9xx(-286)-(-250)`
`=5476kJ//mol`.