Catalysts & Rate of Reactions (Oxford AQA IGCSE Combined Science Double Award)

Catalysts & Rate of Reactions

• Catalysts are substances which speed up the rate of a reaction while remaining chemically unchanged 

  • This means that the mass of a catalyst at the beginning and end of a reaction is the same

• Normally only small amounts of catalysts are needed to have an effect on a reaction

• Catalysts do not form part of the chemical equation but they are sometimes seen above or below the reaction arrow: 

N₂ (g) + 3H₂ (g)  2NH₃ (g)

Graph for the addition of a Catalyst

Graph showing the effect of a catalyst on rate of reaction

• Compared to a reaction without a catalyst, the line graph for the same reaction with a catalyst:

  • Has a steeper gradient at the start

  • Becomes horizontal sooner

  • Forms the same amount of product

• This shows that the addition of a catalyst increases the rate of reaction

Uses of Catalysts

• Catalysts are a very important  branch of chemistry in industry because:

  • They increase the rate of reaction which increases the rate of production

  • They reduce energy requirements which reduces costs

• Examples of industrial processes that use catalysts include:

  • The Haber process:

    N₂ (g) + 3H₂ (g)  2NH₃ (g)

  • The Contact process:

    SO₂ (g) + O₂ (g)  SO₃ (g)

  • Cracking