Sulfur dioxide combines with oxygen in the air. $2\text{SO}_2(\text{g}) + \text{O}_2(\text{g}) \rightleftharpoons 2\text{SO}_3(\text{g}) \quad \Delta H = -196\,\text{kJ mol}^{-1}$ In the absence of a catalyst, the reaction rate is very low. Which statement accounts for this?
- AAir contains only 21% oxygen so there is not enough oxygen for all the sulfur dioxide to react.
- BOnly a small proportion of the sulfur dioxide and oxygen molecules have enough energy to react, even at high temperatures.
- CThe reaction is exothermic and so at high temperatures the equilibrium shifts to the left.
- DThe reaction is reversible and so products turn back to reactants; this happens more quickly at high temperatures.