Catalysts Catalysts speed up the rate of reaction because they make it easier for the particles to react. This means that the particles don’t need to have as much energy to react. Catalysts lower the activation energy required. This can be shown on energy profile diagrams as in Fig. 16
No catalyst catalyst Reactants
Smaller activation energy with catalyst
Products Reaction
Fig. 16 Catalysts lower the activation energy needed for a reaction to take place.
Nature of Science
In this chapter a range of investigations was carried out to find out the effect of temperature, pH, particle size and concentration on some chemical and biochemical reactions. An important part of science is being able to discover things by carrying out investigations, and then applying your findings to a range of different situations. 1. Think about what you discovered in these investigations. Give three real-life examples where knowledge of the effect of these variables on rate of reaction would be helpful.
2. Why is it important for scientists to be able to control (speed up or slow down) the rate of chemical reactions?
Chapter Summary
1. A chemical reaction is a process that involves the rearrangement of atoms, molecules or ions to form new substances.
2. The rate of a chemical reaction is the amount of any one material that is either made or used up per second.
3. Rate of reaction = 4. Rates are measured in s-1
Time taken 1
.
5. Particle size, concentration of a solution, temperature, pH and catalysts can all affect the rate of a reaction.
6. A catalyst is a substance that changes the rate of a chemical reaction without being used up in the reaction.
7. Enzymes are biological catalysts. 8. Exothermic reactions give out energy. 9. Endothermic reactions take in energy.
10. Activation energy is the minimum energy required for a reaction to take place. 11. Energy profile diagrams illustrate the changes in energy that take place during chemical reactions.
