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)+(25)/(2)O_(2)(g)rarr8CO_(2)+9H_(2)O(l)`
`DeltaH_(t)=E(DeltaH_(f)^(@))_("Product")-E(DeltaH_(f)^(@))_("reactant")`
`=[8(-394)+9(-286)]-[-250+0]`
`=[-3152-2574]+250`
`=-5726+250`
`=-5476` kJ/mol