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ChemistryGCSE, IGCSE & A Level

What is catalyst?

A catalyst speeds up a reaction by providing an alternative pathway with a lower activation energy, without being used up itself.

Catalyst explained

Because the activation energy falls, a larger fraction of collisions is successful at the same temperature — draw this on a Maxwell-Boltzmann distribution at A Level.
Catalysts do not change the position of equilibrium; they let the system reach that same position faster, which is why industry values them.

Key formula

Lower EaE_{a}, unchanged ΔH\Delta H

Worked example

Iron catalyses the Haber process, allowing ammonia synthesis at a workable rate and lower temperature.

Examiner tip

Never write that a catalyst lowers the energy of the reactants — it lowers the activation energy by offering a different route.

Catalyst: common questions

What is the difference between a homogeneous and heterogeneous catalyst?
A homogeneous catalyst is in the same physical state as the reactants; a heterogeneous one is in a different state, usually a solid with gaseous reactants.
Do enzymes count as catalysts?
Yes — enzymes are biological catalysts, highly specific to their substrate and sensitive to temperature and pH.

Related terms

Rate of reaction

The rate of reaction is how quickly reactants are used up or products are formed, usually measured as a change in amount per unit time.

Dynamic equilibrium

A dynamic equilibrium is reached in a closed system when the forward and reverse reactions occur at the same rate, so concentrations stay constant.

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