# Solve the following

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______________ $\mathrm{J}$.

(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 Fe is 55.85u ]

Solution:

(2218)

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

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

$50 \mathrm{~g} \quad \mathrm{P}=1 \mathrm{bar}$

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

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

$\rightarrow$ Work done for $1 \mathrm{~mol}$ gas $=-\mathrm{P}_{\text {ext }} \times \Delta \mathrm{V}$

$=\Delta \mathrm{ngRT}$

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

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

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

$=-2218.059 \mathrm{~J}$

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