3. The Collision Theory and Activation Energy Explaining how and why factors affect reaction rates

4. SIMPLE COLLISION THEORY

5. Simple Collision Theory

6. How can we increase high energy collisions? Increase surface area Increase Temperature Increase concentration Anything that increases the rate at which collisions occur will increase the rate of reaction.

7. Increase temperature Particles have more energy. Particles move faster. Particles have MORE EFFECTIVE COLLISIONS PER SECOND. Low Temperature High Temperature

8. Increase concentration If a reactant is more concentrated… … particles are more crowded… … so there are MORE EFFECTIVE COLLISIONS PER SECOND! Low concentration High concentration

9. Increase surface area If surface area is high (as in a powder), less particles will be trapped in the centre. Low surface areaHigh surface area So there are MORE EFFECTIVE COLLISIONS per second.

10. We’ll cover Collision Theory in greater detail in later lessons

11. Why don’t reactions occur spontaneously? Many reactions do not occur spontaneously Most need a “push” to get them going This is because there is an energy barrier between reactants and products. So we have to give the reactant molecules sufficient energy to scale this energy barrier

12. Why don’t reactions occur spontaneously? Once an exothermic reaction gets going, it releases enough energy to activate the rest of the reactant molecules. This energy barrier is an activation energy UNIT: kJ/mol

13. Exothermic Vs Endothermic Exothermic – once we get them going they produce enough energy to become self-sustaining. Endothermic – we have to supply energy continuously.

14. So what effect does activation have? Determines how quickly the rate of reaction increases as temp. increases High activation energy, slow reaction. Low activation energy, fast reaction.

15. Start Reactant energy at 0 kJ/mol