# solve this

Question:

At $25^{\circ} \mathrm{C}, 50 \mathrm{~g}$ of iron reacts with $\mathrm{HCl}$ to form $\mathrm{FeCl}_{2}$. The evolved hydrogen gas expands against a constant pressure of 1 bar. The work done by the gas during this expansion is_____________J

(Round off to the Nearest Integer)

[Given : $\mathrm{R}=8.314 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}$. Assume,

hydrogen is an ideal gas]

[Atomic mass off $\mathrm{Fe}$ is $55.85 \mathrm{u}$ ]

Solution:

$\mathrm{T}=298 \mathrm{~K}, \mathrm{R}=8.314 \frac{\mathrm{J}}{\mathrm{mol} \mathrm{K}}$

$\rightarrow$ Chemical reaction is

$\mathrm{Fe}+2 \mathrm{HCl} \rightarrow \mathrm{FeCl}_{2}+\mathrm{H}_{2}(\mathrm{~g})$

$\begin{array}{ll}50 \mathrm{~g} & \mathrm{P}=1 \text { bar }\end{array}$

$=\frac{50}{55.85} \mathrm{~mol}$

$\frac{50}{55.85} \mathrm{~mol}$

$\rightarrow$ Work done for $1 \mathrm{~mol}$ gas

$=-\mathrm{P}_{\mathrm{ext}} \times \Delta \mathrm{V}$

$=\Delta \mathrm{ng} \mathrm{RT}$

$=-1 \times 8.314 \times 298 \mathrm{~J}$

$\rightarrow$ Work done for $\frac{50}{55.85} \mathrm{~mol}$ of gas

$=-1.8314 \times 298 \times \frac{50}{55.85} \mathrm{~J}$

$=-2218.059 \mathrm{~J}$

$\simeq-2218 \mathrm{~J}$