Heat of combustion `DeltaH^(@)` for `C(s),H_(2)(g)` and `CH_(4)(g)` are `94, -68` and `-213Kcal//mol` . Then `DeltaH^(@)` for `C(s)+2H_(2)(g)rarrDeltaCH_(4)(g)` is

Options

A. `-17` kcal/mol
B. `-111` kcal/mol
C. `-170 ` kcal/mol
D. `-85 ` kcal/mol

Answer

A

Explanation

For reaction
`C(s) + 2H_(2)(g) to CH_(4)(g), DeltaH^(@)C=? `
`C+O_(2) to CO_(2), DeltaH=-94 ` kcal …(i)
`2H_(2)+ O_(2) to 2H_(2)O, DeltaH=-68 xx 2` kcal …(ii)
`CH_(4)+ 2O_(2) to CO_(2) + 2H_(2)O, DeltaH=-213` Kcal …(iii)
On adding Eqs. (i) and (ii) and then subtracting Eq. (ii)
`=(-94) + (-2xx68)-(-213)`
`-230 + 213 =-17 `K cal/mol