The molar heats of combustion of C_(2)H_(2)(g), C (graphite) and H_(2)(g) are 310.62 kcal, 94.05 kcal and 68.32 kcal respectively. Calculate the standard heat of formation of C_(2)H_(2)(g).

The molar heats of combustion of C_(2)H_(2)(g), C (graphite) and H_(2)

1.	The molar heats of combustion of C_(2)H_(2)(g), C (graphite) and H_(2)(g) are 310.62 kcal, 94.05 kcal and 68.32 kcal respectively. Calculate the standard heat of formation of C_(2)H_(2)(g).
Answer» Solution :Given that, (i) `{:(C(s)+O_(2)(g) to CO_(2)(g),,DELTAH=-94.05"KCAL"):}` (ii) `{:(H_(2)(g)+(1)/(2)O_(2)(g) to H_(2)O(g),,DeltaH=-68.32"kcal"):}` (III) `{:(C_(2)H_(2)(g)+2(1)/(2)O_(2)(g) to 2CO_(2)(g)+H_(2)O(g),,DeltaH=-310.62"kcal"):}` We have to calculate `DeltaH` of the equation `2C(s)+H_(2)(g) to C_(2)H_(2)(g),DeltaH=?` Proceeding the same way as in Example 9, we apply, [2xx Eqn. (i)+Eqn.(ii) - Eqn. (iii)] and we GET, `2C(s)+2O_(2)(g)+H_(2)(g)+(1)/(2)O_(2)(g)-C_(2)H_(6)(g)-2(1)/(2)O_(2)(g) to 2CO_(2)(g)+H_(2)O(g)-2CO_(2)(g)-H_(2)O(g),DeltaH=2xx(-94.05)+(-68.32)-(-310.62)` or `2C(s)+H_(2)(g) to C_(2)H_(2)(g),DeltaH=54.20"kcal"`