Dihydrogen gas is obtained from natural gas by partial oxidation with steam as per the following endothermic reaction:
$CH_{4(g)} + H_2O_{(g)} \rightleftharpoons CO_{(g)} + 3H_{2(g)}$
$(a)$ Write an expression for $K_p$ for the above reaction.
$(b)$ How will the values of $K_p$ and the composition of the equilibrium mixture be affected by:
$(i)$ increasing the pressure
$(ii)$ increasing the temperature
$(iii)$ using a catalyst?

(A) The expression for the equilibrium constant $K_p$ is:
$K_p = \frac{p_{CO} \times p_{H_2}^3}{p_{CH_4} \times p_{H_2O}}$
$(b)$ $(i)$ Increasing the pressure shifts the equilibrium in the backward direction because the number of moles of gaseous products $(4 \ mol)$ is greater than the number of moles of gaseous reactants $(2 \ mol)$. $K_p$ remains unchanged as it depends only on temperature.
$(ii)$ Increasing the temperature shifts the equilibrium in the forward direction because the reaction is endothermic $(\Delta H > 0)$. Consequently,the value of $K_p$ increases.
$(iii)$ Using a catalyst does not affect the equilibrium position or the value of $K_p$. It only increases the rate at which the equilibrium is attained.