For this question, assume that all gases behave ideally. Hydrogen and iodine react reversibly in the reaction shown below. The system then attains dynamic equilibrium. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$ $\Delta H = -9.5\,\text{kJ mol}^{-1}$. Which statement must be true for the $K_p$ of this equilibrium to be constant?
- AThe partial pressures of $\text{H}_2$, $\text{I}_2$ and $\text{HI}$ are equal.
- BThe external pressure is constant.
- CThe forward and reverse reactions have stopped.
- DThe temperature is constant.