A gas (Molar mass = 280 $\mathrm{~g} \mathrm{~mol}^{-1}$) was burnt in excess $\mathrm{O}_{2}$ in a constant volume calorimeter and during combustion the temperature of calorimeter increased from $298.0 \mathrm{~K}$ to $298.45$ $\mathrm{K}$. If the heat capacity of calorimeter is $2.5 \mathrm{~kJ} \mathrm{~K}^{-1}$ and enthalpy of combustion of gas is $9 \mathrm{~kJ} \mathrm{~mol}^{-1}$ then amount of gas burnt is _____________ g. (Nearest Integer)
Answer (integer)
35
Solution
$\Delta \mathrm{U}=\mathrm{C} \Delta \mathrm{T}$
<br/><br/>
$$
\begin{aligned}
&=2.5 \times 10^{3} \times 0.45 \\\\
&=1.125 \mathrm{~kJ}
\end{aligned}
$$
<br/><br/>
Considering $\Delta \mathrm{H} \simeq \Delta \mathrm{U}$
<br/><br/>
$\Delta \mathrm{H}=9 \mathrm{~kJ} / \mathrm{mol} \simeq \Delta \mathrm{U}$
<br/><br/>
$\therefore$ Mass of gas burnt $=\frac{1.125}{9} \times 280=35 \mathrm{~g}$
About this question
Subject: Chemistry · Chapter: Thermodynamics · Topic: Zeroth and First Law
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