Temperature
An increase in temperature usually, increases the rate of a reaction. Cooking at sea level takes less time than on the mountain top because water boils at higher temperature at sea level than at the mountain top.
Catalyst
A catalyst usually speeds up the rate of reaction, although it is not consumed in the reaction. Oxidation of sulphur dioxide (SO2) to sulphur trioxide (SO3) is a very slow reaction. However, this reaction accelerates in the presence of nitric oxide (NO).
