A catalyst is a substance (usually a transition metal) which speeds up a chemical reaction, but remains unchanged at the end
Adding a catalyst increases the rate of reaction
A catalyst allows the reaction to go by an alternative pathway with lower activation energy
More particles will have an energy greater than or equal to the activation energy, therefore successful collision rate increases resulting in increased rate of reaction
For gaseous reactants, if catalyst is solid metal, the catalyst provides a surface for reaction to take place on
The larger the surface area of the metal catalyst, the larger the area for reaction to take place therefore the higher rate of reaction
Enzymes are biological catalysts which speed up reactions but remain chemically unchanged at the end
Enzymes function best at optimum temperature and pH level otherwise they may denature and completely stop functioning