Chemistry C2 Part three

1. Chemistry C2 Part three Revision PowerPoint - Big ideas Chemical reactionscollisions and energy

2. Speeding up chemical reactions • The rate of reaction is the change in the amount of product or reactant per second. • Reactions are faster at higher temperatures, at high concentrations or high pressure, and with powdered solids.

3. Particle collisions and energy • In order for a chemical reaction to occur particles must collide with sufficient energy for their chemical bonds to break • Any factor which affects the number of violent collisions will increase the rate of reaction.

4. Catalysts and activation energy • Activation energy is the minimum amount of energy particles need to react. • Catalysts speed up the rate of slow reactions but are unchanged at the end. They reduce the cost of industrial reactions.

5. Exothermic or endothermic? • Most reactions, e.g. combustion of fuels and neutralisation, are exothermic and give out energy intothe surroundings, which become warmer. • Other reactions are endothermic, e.g. electrolysis and photosynthesis, and take in energy from the surroundings

6. Reversible reactions • Reversible reactions are endothermic in one direction and exothermic in the other.e.g. heating hydrated copper sulphate is endothermic, but adding water to anhydrous copper sulphate is exothermic

7. Endothermic reactions Endothermic reactions create products with higher chemical energy than the reactants Thermal energy is changed into chemical energy; the surroundings get colder.

8. Exothermic reactions Exothermic reactions create products with lower chemical energy than the reactants Chemical energy is changed into thermal energy; the surroundings get warmer.