Question

Calculate the standard heat of formation of $C_{10}{H}_8$ (naphthalene) if standard heat of combustion of naphthalene is $-1231.0kcal$ at $298K$ and standard heats of formation of $C{O}_2\left(g\right)$ and $H_{2}O\left(l\right)$ are $-94.0kcal$ and $-68.4kcal$ respectively.

• A. 14.4 kcal
• B. 17.4 kcal
• C. 16.4 kcal
• D. 15.4 kcal

Answer 1

The correct option is B 17.4 kcal

Standard heat of formation of $C_{10}{H}_8$ = 10$\times$heat of formation of $C{O}_2$ + 4$\times$ heat of formation of water - heat of combustion of naphthalene.

Heat of formation of $C_{10}{H}_8$ = $10\ast (-94)+(-68.4)-\left(1231\right)$ = $17.4kcal$