Wk6 session 1 rates
- 1. Effective from September 2015 | Plus term chemistry Wk6 – session 1 Joanne Lumley Week 6 – session 1 Rates of Reactions
- 2. Effective from September 2015 | Plus term chemistry Wk6 – session 1 In Contact • Reactions don’t happen unless the substances are in contact.
- 3. Effective from September 2015 | Plus term chemistry Wk6 – session 1 Why? • The particles of the reactants need to get together so that they can react.
- 4. Effective from September 2015 | Plus term chemistry Wk6 – session 1 How? Reactant particles collide Product particles formed REACTION
- 5. Effective from September 2015 | Plus term chemistry Wk6 – session 1 Not all collisions are effective • Paper burns • Paper + oxygen carbon dioxide + water + nitrogen • The paper in this room isn’t burning. • It doesn’t have enough energy to burn. • If we make it hotter it will catch fire. • Paper burns on its own at 250 ºC
- 6. Effective from September 2015 | Plus term chemistry Wk6 – session 1 A collision but with no effect Reactant particles collide Product particles not formed as there is not enough energy
- 7. Effective from September 2015 | Plus term chemistry Wk6 – session 1 Activation Energy • Reactions only happen if the particles have enough energy. • The minimum amount of energy needed to start a reaction is called the Activation Energy • The amount of activation energy needed is different for each reaction. • But • Every reaction has activation energy, they all need a little push to get started.
- 8. Effective from September 2015 | Plus term chemistry Wk6 – session 1 More than the activation energy. Reactant particles collide Product particles formed REACTION
- 9. Effective from September 2015 | Plus term chemistry Wk6 – session 1 More than the activation energy. C O O CO O Effective collisions, a reaction.
- 10. Effective from September 2015 | Plus term chemistry Wk6 – session 1 The Collision Theory • Particles are constantly moving • For a chemical reaction to take place the reactant particles must collide first • For the collision to be effective the particles must have the right amount of energy • The minimum amount of energy required for an effective collision is called the activation energy
- 11. Effective from September 2015 | Plus term chemistry Wk6 – session 1 Factors affecting rate • Concentration • Temperature • Catalysts • Surface Area
- 12. Effective from September 2015 | Plus term chemistry Wk6 – session 1 Concentration • More particles in the same space means more collisions. • More collisions means more effective collisions • If we double the concentration we double the number of collisions
- 13. Effective from September 2015 | Plus term chemistry Wk6 – session 1 Temperature • Particles turn heat energy into kinetic energy • When they get hotter they move faster • When they move faster they collide more often • More collisions means more effective collisions
- 14. Effective from September 2015 | Plus term chemistry Wk6 – session 1 Catalysts • Catalysts reduce the activation energy needed for a reaction • They do this by offering an alternate route for the reaction to take • Less activation energy means more effective collisions • More effective collisions means faster rate Activation energy with a catalyst
- 15. Effective from September 2015 | Plus term chemistry Wk6 – session 1 Surface Area/Particle Size • Using smaller particles increases rate • Increase in surface area allows more collisions at surface • More collisions means more effective collisions means faster rate.