The heat of formations for `CO_(2)(g),H_(2)O(l) and CH_(4)(g)` are -400 kJ `mol^(-1),-280" kJ "mol^(-1) and -70" kJ "mol^(-1)`, respectively. The heat of combustion of `CH_(4)` in kJ `mol^(-1)` is

Options

A. `890`
B. `-160`
C. `-890`
D. `-90`

Answer

C

Explanation

`DeltaH_("reaction")=sumDeltaH_(i)("product")-sumDeltaH_(f)("reactant").`
`DeltaH_(f)` of a single element like `O_(2),H_(2),Cl_(2)` is considered equal to zero.
`CH_(4)+2O_(2) to CO_(2)+2H_(2)O`
`DeltaH_("reaction")=DeltaH_(f)(CO_(2))+2DeltaH_(f)*(H_(2)O)-DeltaH_(f)(CH_(4))-2DeltaH_(f)(O_(2))`
`=-400+2(-280)-(-70)-0=-890` kJ `mol^(-1)`