Reaction Rates

1. Reaction Rates

2. Collision Theory • In order for reactions to occur, particles must collide • If collisions are too gentle, no reaction occurs • If collisions do not occur at the correct angle, no reaction occurs

3. Activation Energy • In order for reaction to occur, the old bonds of the substances must be broken before new bonds can form • Breaking the bonds is always endothermic while forming new bonds is exothermic • Even though an overall reaction is exothermic, it may require an initial input of energy to get the bonds broken – called activation energy (Ea)

4. Activated Complex • An intermediate structure that atoms are in while breaking old bonds and making new ones

5. Reactants Energy Products Reaction coordinate

6. Activation Energy (E a ) - Minimum energy to make the reaction happen Reactants Energy Products Reaction coordinate

7. Activated Complex or Transition State Reactants Energy Products Reaction coordinate

8. Reactants Energy Overall energy change (H) Products Reaction coordinate

9. Reaction Rate • Speed of a reaction • Measured by the change in concentration of reactants or products over time • As the reaction proceeds the concentration of reactants will decrease and the concentration of products will increase

10. Factors Affecting Reaction Rate • Changing conditions may affect the collision frequency or collision efficiency and this will affect the speed of the reaction • Five important factors influence the rate

11. 1) Nature of Reactants – some substances are more reactive 2) Surface area – greater surface area faster reaction 3) Concentration – greater concentration, faster the reaction 4) Temperature – greater temp, faster reaction

12. 5) Catalyst Substance not part of the reaction but makes the reaction faster by lowering the activation energy

13. Reactants Energy Products Reaction coordinate