The following are heats of reactions `:`
`(A)` `DeltaH_(f)^(@)` of `H_(2)O(l)=-68.3kcal` `mol^(-1)`
`(B)` `DeltaH_(comb)^(@)` of `C_(2)H_(2)=-337.2 kcal` `mol^(-1)`
`(C)` `DeltaH_(comb)^(@)` of `C_(2)H_(4)=-363.7Kal` `mol_(-1)`
Then the heat charge for the reaction `:-`
`C_(2)H_(2)+H_(2)rarrC_(2)H_(4)`

Options

A. `-716.1` K cal
B. `+337.2` K cal
C. `-41.8` K cal
D. `-579.5` K cal

Answer

C

Explanation

`H_(2(g))+(1)/(2)O_(2(g))rarr H_(2)O_((l)) , Delta H = Delta H_(f)(H_(2)O)` and `Delta H_("comb.")(H_(2))`
`C_(2)H_(2)+H_(2)rarr C_(2)H_(4) , Delta H = ?`
`Delta H = Sigma (Delta H_("comb"))_(R )-Sigma (Delta H_("comb"))_(P)`
`=[(-337.2)+(-68.3)]-(-363.7)`
`Delta H=-41.8` kCal