Question

In a constant volume calorimeter, $3.5 \,g$ of a gas with molecular weight $28$ was burnt in excess oxygen at $298.0 \,K$. The temperature of the calorimeter was found to increase from $298.0 K$ to $298.45 K$ due to the combustion process. Given that the heat capacity of the calorimeter is $2.5 \,kJ K ^{-1}$, the numerical value for the enthalpy of combustion of the gas in $kJmol ^{-1}$ is

Answer 1

Energy release at constant volume due to combustion of $3.5\, gm$ of a gas $=2.5 \times 0.45$
Hence energy released due to the combustion of $28\, gm$ (i.e., 1 mole) of a gas
$=2.5 \times 0.45 \times \frac{28}{3.5}=9 \,kJmol ^{-1}$