The heat of combustion of naphthalene (s) is -123.25 kcal. If the heats of formation of CO_(2)(g) and H_(2)O (l) are -97.0 and -68.4 kcal respectively. Calculate the heat of formation of naphthalene.

The heat of combustion of naphthalene (s) is -123.25 kcal. If the heat

1.	The heat of combustion of naphthalene (s) is -123.25 kcal. If the heats of formation of CO_(2)(g) and H_(2)O (l) are -97.0 and -68.4 kcal respectively. Calculate the heat of formation of naphthalene.
Answer» Solution :Given that, (i) `C_(10)H_(8)(s)+12O_(2)(g) to 10CO_(2)(g)+4H_(2)O(l),DeltaH=-123.25"kcal"` (II) `C(s)+O_(2)(g) to CO_(2)(g),DeltaH=-97.0"kcal"` (iii)`H_(2)(g)+(1)/(2)O_(2)(g) to H_(2)O(l),DeltaH=-68.4"kcal"` We have to calculate `DeltaH` of the EQUATION, `10C(s)+4H_(2)(g) to C_(10)H_(8)(s),DeltaH=?` Applying the inspection method, [-Eqn.(i)+10xxEqn. (ii)+4xxEqn.(iii)], we get, `-C_(10)H_(8)(s)-12O_(2)(g)+10C(s)+10O_(2)(g)+4H_(2)(g)+2O_(2)(g) to -10CO_(2)(g)-4H_(2)O(l)+10CO_(2)(g)+4H_(2)O(l),DeltaH=-(-123.25)+10xx(-97.0)+4xx(-68.4)` or `10C(s)+4H_(2)(g) to C_(10)H_(8)(s),DeltaH=-1120.35"kcal"`