Q60 / 200 · NEET 2006 · Chemistry
For the reaction:
$$
\mathrm{CH}_{4(g)}+2 \mathrm{O}_{2(g)} \rightleftharpoons \mathrm{CO}_{2(g)}+2 \mathrm{H}_2 \mathrm{O}(l)
$$
$\Delta \mathrm{H}_r=-170.8 \mathrm{~kJ} \mathrm{~mol}^{-1}$. Which of the following statements is not true?
- AThe reaction is exothermic
- BAt equilibrium, the concentrations of $\mathrm{CO}_{2(g)}$ and $\mathrm{H}_2 \mathrm{O}_{(h)}$ are not equal
- Correct answerCThe equilibrium constant for the reaction is given by $\mathrm{K}_p=\frac{\left[\mathrm{CO}_2\right]}{\left[\mathrm{CH}_4\right]\left[\mathrm{O}_2\right]}$
- DAddition of $\mathrm{CH}_{4(g)}$ or $\mathrm{O}_{2(g)}$ at equilibrium will cause a shift to the right
Solution
For the reaction,
$$
\begin{gathered}
\mathrm{CH}_{4(\mathrm{~g})}+2 \mathrm{O}_{2(\mathrm{~g})} \rightarrow \mathrm{CO}_{2(\mathrm{~g})}+2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{I})} \\
\Delta \mathrm{H}_r=-170.8 \mathrm{~kJ} \mathrm{~mol}^{-1}
\end{gathered}
$$
From the above reaction,
$$
\mathrm{K}_c=\frac{\left[\mathrm{CO}_2\right]}{\left[\mathrm{CH}_4\right]\left[\mathrm{O}_2\right]^2}
$$
$$
\mathrm{K}_p=\frac{\mathrm{P}_{\mathrm{CO}_2}}{\mathrm{P}_{\mathrm{CH}_4} \times \mathrm{P}_{\mathrm{O}_2^2}}
$$
So, $\quad \mathrm{K}_p=\frac{\left[\mathrm{CO}_2\right]}{\left[\mathrm{CH}_4\right]\left[\mathrm{O}_2\right]^2}$ is incorrect.
Hence, the correct answer is option: 'C'.