Find the heat of formation of ethal alcohol from following data :
`{:(C(s)+O_(2)(g)rarrCO_(2)(g)",",,Delta H=-94 kcal),(H_(2)(g)+(1)/(2)O_(2)(g)rarr H_(2)O(l)",",,Delta H=-68 kcal),(C_(2)H_(5)O(l)+3O_(2)(g)rarr 2CO_(2)(g)+3H_(2)O(l)",",,Delta H=-327 kcal):}`

Explanation

On the basis of definition of formation, the following hermochemical equation is written for which `Delta H_(f)` is to be calculated : `2C(s)+3H_(2)(g)+(1)/(2)O_(2)(g)rarr C_(2)H_(5)OH(l),Delta H_(f) = ?`
Given data may be written as follows because thermochemical equation act as algebraic equations
`{:((i),2C(s)+2O_(2)(g)rarr2CO_(2)(g),,Delta H=-188 kcal),((ii),3H_(2)(g)+(3)/(2)O_(2)(g)rarr 3H_(2)O(l)",",,Delta H=-204 kcal),((iii),2CO_(2)(g)+3H_(2)O(l)rarr C_(2)H_(5)OH(l)+3O_(2)(g),,Delta H=+327 kcal),(,"On addition "2C(s)+3H_(2)(g)+(1)/(2)O_(2)(g)rarr C_(2)H_(5)OH(l)",",,Delta H_(f)=-65 kcal//mol.):}`