Catalysts (Edexcel IGCSE Chemistry: Double Science)

Revision Note

Test yourself
Stewart

Author

Stewart

Last updated

The effect of a catalyst on rate of reaction

  • Catalysts are substances which speed up the rate of a reaction without themselves being altered or consumed in the reaction
    • Normally only small amounts of catalysts are needed to have an effect on a reaction
    • The mass of a catalyst at the beginning and end of a reaction is the same 
  • Catalysts do not form part of the chemical equation but they are sometimes seen above or below the reaction arrow: 

N2 (g) + 3H2 (g) rightwards harpoon over leftwards harpoon from 450 space degree straight C comma space 200 space atm to iron space catalyst of
 2NH3 (g)

SO2 (g) + O2 (g) rightwards arrow from straight V subscript 2 straight O subscript 5 space catalyst to 450 space degree straight C of SO3 (g)

  • Different processes require different types of catalysts but they all work on the same principle:
    • They provide an alternative pathway for the reaction to occur
    • The alternative pathway has a lower activation energy

Diagram showing how iron acts as a catalyst for the Haber process

Reaction Kinetics - Iron Catalyst (2), downloadable AS & A Level Chemistry revision notes

Catalysts work by attracting reactant molecules on to the surface and so providing an alternate reaction pathway of lower energy

  • Catalysis is a very important  branch of chemistry in commercial terms as catalysts increase the rate of reaction (hence the production rate) and they reduce energy costs
  • The transition metals are used widely as catalysts as they have variable oxidation states allowing them to readily donate and accept different numbers of electrons
    • This is key to their catalytic activity
  • Enzymes act as catalysts in biological systems

Examiner Tip

The effect of a catalyst on activation energy can be shown on a reaction profile

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Stewart

Author: Stewart

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.