Catalyst

A catalyst lowers activation energy; it does not give particles more energy or change the overall energy change of the reaction.

Identify a catalyst using both its effect on reaction rate and the fact that it is not used up. Absence from an equation alone is not enough.

For catalytic cracking, describe vaporising the hydrocarbon and passing its vapour over a hot catalyst. For steam cracking, describe mixing the vapour with steam and heating to a very high temperature.