Question

The heat linerated when $1.89g$ of benzoic acid is burnt in a bomb calorimeter at ${25}^{o}C$ increases the temperature of $18.94kg$ of water by ${0.632}^{o}C$. If the specific heat of water at ${25}^{o}C$ is $0.998cal{g}^{-1}$ ${deg}^{-1}$, the value of heat of combustion of benzoic acid is:

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

Answer 1

The correct option is B $771.4kcal$

$\text{Given, weight of benzoic acid =1.89g}$

$\text{Temperature of bomb calorimeter=25 degree celsius}$

$\text{Mass of water (m)= 18.94 kg=18940g}$

$\text{Increse in temperature(T)=0.632}$

$\text{and specific heat of water(s)=0.998 cal/g/deg}$

$\text{We know that heat gained by water or heat liberated by benzoic acid(Q)=}$

$ms\delta T=18940\ast 0.998-0.632=11946.14cal$

$textSince,1.89gofacidliberates11946.14calofheat,$

$\text{hence, heat liberated by 112g of acid(1 mol)=}$ $\frac{11946.14X112}{1.89}=771.12kcal$