When iodine vapour is heated together with hydrogen at $450\,^{\circ}\text{C}$, an equilibrium is formed. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g) \qquad \Delta H = +53\,\text{kJ mol}^{-1}$ $\text{H}_2$ colourless, $\text{I}_2$ purple, $\text{HI}$ colourless. Which change in conditions would make the purple colour of the equilibrium mixture less intense?
- Adecrease in pressure
- Bdecrease in temperature
- Cincrease in pressure
- Dincrease in temperature