Rates of Reaction

What a catalyst is

• A catalyst is a substance that speeds up a chemical reaction without being used up in it
• The mass of the catalyst is the same at the end of the reaction as at the start
• Only small amounts of catalyst are usually needed because each particle of catalyst can take part in many reactant turnovers
• A catalyst is neither a reactant nor a product, so its formula is written next to the arrow itself rather than inside the balanced equation

Industrial examples of catalysts

• Many catalysts are transition metals or their oxides — their variable oxidation states allow them to accept and donate electrons easily, which is what makes them catalytic
• Enzymes are biological catalysts: protein molecules that accelerate specific reactions inside cells

How a catalyst works

• A catalyst provides an alternative reaction pathway that has a lower activation energy than the uncatalysed route
• More reactant particles now have at least the (lower) activation energy at any given temperature, so a larger proportion of every collision is successful
• The catalyst is not consumed because it is regenerated at the end of the alternative pathway