1. “Reaction Rates and Equilibrium” Activation Energy is being supplied Activated Complex OBJECTIVES: Describe how to express the rate of a chemical reaction. Identify four factors that influence the rate of a chemical reaction

2. Collision Theory   Reactions can occur: – –Very fast – such as a firecracker – –Very slow – such as the time it took for dead plants to make coal – –Moderately – such as food spoilage   A “rate” is a measure of the speed of any change that occurs within an interval of time   In chemistry, reaction rate is expressed as the amount of reactant changing per unit time. Example: 3 moles/year, or 5 grams/second

3. I wonder what happens if I mix these two solutions… WOW, that was really FAST It was also really FUN

4. Collision Theory  Reaction rate depends on the collisions between reacting particles.  Successful collisions occur if the particles... –collide with each other –have the correct orientation –have enough kinetic energy to break bonds

5. Collision Theory Key Idea: The molecules must touch (or collide) to react. However, only a small fraction of collisions produces a reaction. Why? Particles lacking the necessary kinetic energy to react will bounce apart unchanged when they collide

6. Collision Theory   Collisions must have enough energy to produce the reaction   activation energy: the minimum energy needed for a reaction to occur Activation Energy

7. Collision Theory   activated complex: an unstable arrangement of atoms that forms momentarily at the peak of the activation-energy barrier. – –This is sometimes called the transition state   Results in either a) forming products, or b) reformation of reactants – –Both outcomes are equally likely

8. - Page 543 a. Reactants b. Absorbedc. No; it could also revert back to the reactants

9. Factors Affecting Rxn Rate  Surface Area –high SA = fast rxn rate –more opportunities for collisions –Increase surface area by…  using smaller particles  dissolving in water

10. Factors Affecting Rxn Rate  Concentration –high concentration = fast rxn rate –more opportunities for collisions

11. Factors Affecting Rxn Rate  Temperature –high temp = fast rxn rate –high KE  fast-moving particles  more likely to reach activation energy

12. Factors Affecting Rxn Rate  Catalyst –substance that increases rxn rate without being consumed in the rxn –lowers the activation energy

13. Endothermic Reaction with a Catalyst

14. Exothermic Reaction with a Catalyst