For the reaction $CH_4(g) + 2O_2(g) \rightleftharpoons CO_2(g) + 2H_2O(l)$,the enthalpy change is $\Delta H_r = -170.8 \, kJ \, mol^{-1}$. Which of the following statements is $NOT$ true?

• A
  At equilibrium,the concentrations of $CO_2(g)$ and $H_2O(l)$ are not equal.
• B
  The equilibrium constant for the reaction is given by $K_p = \frac{P_{CO_2}}{P_{CH_4} \cdot P_{O_2}^2}$.
• C
  Adding $CH_4(g)$ or $O_2(g)$ at equilibrium shifts the reaction to the right.
• D
  The reaction is exothermic.