Chemistry - Thermodynamics - II Question with Solution | TestHub

Vapor Pressure of Water: For H₂O(l) $\rightleftharpoons$ H₂O(g), $\Delta G^{\circ }=-230.7-(-239.0)=8.3kJ/mol$, giving constant $P_{H_{2}O}=e^{-\frac{8300}{8.3\times 300}}=e^{-3.33}\approx 0.036bar$.

Equilibrium Constant ($K_p$): For CO(g) + H₂O(g) $\rightleftharpoons$ CO₂(g) + H₂(g), ${\Delta }_r{G}^{\circ }=-393.9-(-138.3-230.7)=-24.9kJ/mol$, so $K_p=e^{10}\approx 2.2\times 10^4$.

Equilibrium Pressures: Since $K_p$ is very large, CO is mostly consumed. Let $P_{CO}=p$, then $P_{C{O}_2}=P_{H_2}\approx 1+1=2bar$.

Calculation: Substituting into $K_p=\frac{P_{C{O}_2}\cdot P_{H_2}}{P_{CO}\cdot P_{H_{2}O}}⟹2.2\times 10^4=\frac{2\times 2}{p\times 0.036}⟹p\approx 5.05\times 10^{-3}\mathbf{bar}$ (Option B).