Science
Science
WEEK 6
NOTES
CATALYSTS Catalysts change the rate of chemical reactions but are not used up during the reaction. This means that the catalyst is still there, unchanged, at the end of the reaction. Different reactions need different catalysts. Enzymes act as catalysts in biological systems. Carbohydrase is an enzyme/catalyst that only breaks down carbohydrate. Chlorophyll is the catalyst that enables carbon dioxide and water to react together to make glucose during photosynthesis. Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy. A reaction profile for a catalysed reaction can be drawn as shown here. The graphs show how the energy changes in a reaction are different with an enzyme, but the graph is the same shape for any type of catalyst, not just a biological catalyst. You should be able to explain catalytic action in terms of activation energy. For example, “from the reaction profile I can see that the catalyst lowers the activation energy”.
CHECK YOU’RE UNDERSTANDING
20
1. What is meant by the term ‘collision theory’? 2. What is meant by the term ‘activation energy’? 3. What happens to the gradient of a line if the rate of reaction is increased? 4. What is a catalyst? 5. According to collision theory, chemical reactions can only occur when... 6. Other than concentration give three factors that affect the rate of reaction.
YEAR 10 S UMMER BO O KL ET
7. Draw a labelled graph to show how changing any one of these factors may affect the rate of reaction. Include the line before and after the change.
8. What is a catalyst? 9. The symbol equation for photosynthesis is: 6CO2 + 6H2O C6H12O6 + 6O2 The catalyst for this reaction is chlorophyll, however it does not appear in the equation. Why is this?
Delta Academies Trust
YEA R 10 SUM M ER B OOK L ET
Delta Academies Trust
21
