The ratio of rate constants for the forward and backward reactions gives us the equilibrium constant, $K_c$. For a sample reaction:
$$ \ce{A \underset{k_{-1}}{\overset{k_1}{<=>}} P + Q}\quad \Longrightarrow \quad K_c = {k_1\over k_{-1}} = {C_P C_Q\over C_A} $$
Per kinetic theory, rate constants depend only on temperature and the presence of any catalysts:
$$ k_i = A_i e^{-E_{a,i}\over RT} $$
Thus, their ratio (i.e., the equilibrium constant, $K_c$) also must depend only on temperature:
So: Why does $K_x$, the mole-fraction equilibrium constant, depend on pressure and volume?