- Catalysts are substances which speed up the rate of a reaction without themselves being altered or consumed in the reaction.
- The mass of a catalyst at the beginning and end of a reaction is the same and they do not form part of the equation nor do they participate chemically in the formation of the products.
- An industrially important example is iron, which is used to catalyse the Haber Process for the production of ammonia.
- Iron beads are used to increase the surface area available for catalysis.
- Normally only small amounts of catalysts are needed to have an effect on a reaction.
- Different processes require different types of catalysts but they all work on the same principle of providing an alternate route for the reaction to occur.
- They do this by lowering the activation energy required, hence providing a reaction pathway of least resistance by way of requiring less energy.
- Catalysis is a very important branch of chemistry in commercial terms as catalysts increase the rate of reaction (hence the production rate) and reduce energy costs.
- The transition metals are used extensively in this area as they readily donate and accept different numbers of electrons due to their having variable oxidation states.
- This allows them to flood reaction mixtures with electrons and mop up any leftovers before the next batch of reactants is added to the reactor.
Nickel is used to catalyse the production of ethane from ethylene
- Catalysts work by decreasing the activation energy of a particular reaction by providing an alternative reaction pathway which requires less energy.
- This means that a higher percentage of the particles will have the minimum energy required to react, hence there is a higher number of successful collisions.
- Therefore more product molecules are produced in a shorter time, thus increasing the rate of reaction.
- Reaction profile graphs show the relative energy levels of reactants and products on a graph.
- The reaction profile graph below shows the effect of catalysts on reactions.
Graph showing the effect of the use of a catalyst on the rate of reaction
- Catalysts reduce the activation energy as they create alternative pathways requiring lower activation energy, allowing more successful and frequent collisions.
- This shows that when a catalyst is used, the rate of reaction will increase.
- Enzymes are nature’s catalysts.
- They are biological substances that catalyse reactions in living cells.
- Important reactions that are biologically catalysed include respiration, photosynthesis and protein synthesis.
- The production of alcohol by the fermentation of sugars occurs in the presence of a biological catalyst, yeast enzymes:
C6H12O6 + enzymes → 2CO2+ 2C2H5OH
AQA GCSE Chemistry Notes
Want to aim for a Level 9?
See if you’ve got what it takes. Test yourself with our topic questions.
More AQA GCSE (9-1) Chemistry Revision Resources
Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.