Question

The following are the heats of reactions -
(i) `Delta H_(f)^(@)` of `H_(2)O_((l))=-68.3 "K cal mol"^(-1)`
(ii) `Delta H_("comb.")^(@)` of `C_(2)H_(2)=-337.2 "K cal mol"^(-1)`
(iii) `Delta H_("comb.")^(@)` of `C_(2)H_(4)=-363.7 "K cal mol"^(-1)`
Then heat change for the reaction `C_(2)H_(2)+H_(2)rarr C_(2)H_(4)` is -
A. `-716.1 kcal`
B. `+337.2 kcal`
C. `-41.8 kcal`
D. `-579.5 kcal`

Answer 1

Correct Answer - C
Add eqn. `(i)` and `(iii)` and subtract equation `(ii)`