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 formation of `CO_(2)(g)` and `H_(2)O(l)` are `-394 kJ//mol` and `-286kJ//mol` respectively.
A. `- 5200` kJ/mol
B. `- 5726` kJ/mol
C. `- 5476` kJ/mol
D. `- 5310` kJ/mol

Answer 1

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