Question

The heat liberated when $1.89g$ of benzoic acid is burnt in a bomb calorimeter at $25^{\circ }C$ increases the temperature of $18.94kg$ of water by $0.632^{\circ }C$. If the specific heat of water at $25^{\circ }C$ is $0.998cal/g$ the value of the heat of combustion of benzoic acid is

• A. 881.1 kcal
• B. 771.4 kcal
• C. 981.1 kcal
• D. 871.2 kcal

Answer 1

Answer: (B)

Heat capacity, $C_V=18.94\times 0.998\times 10^3$
$=18.902\times 10^{3}cal/deg$
Moles of benzoic acid $=\frac{1.89}{122}$
$C_p=C_v+R$
$=18.902\times 10^3+2$
$=18.904\times 10^{3}cal$
Heat of combustion $=\frac{C_p\times \Delta t}{\text{ moles }}$
$=\frac{18.904\times 10^3\times 0.632\times 122}{1.89}$
$=771.2\times 10^{3}cal$
$=771.2kcal$