2. Kinetics (Reaction Rate) How Fast Does the Reaction Go

3. Collision Theory l In order to react molecules and atoms must touch each other. l They must hit each other with enough force and with the correct orientation. l The more “frequently” the particles hit, the faster the reaction will go. l Anything that increase these effective collisions will make the reaction faster.

4. Factors that Affect Rate l Temperature – Higher temperature faster particles. – More and harder collisions. – Faster Reactions. l Concentration – More concentrated closer together the molecules. – Collide more often. – Faster reaction.

5. Factors that Affect Rate l Particle size – Molecules can only collide at the surface. – Smaller particles bigger surface area. – Smaller particles faster reaction. – Smallest possible are molecules or ions. l Dissolving speeds up reactions. – Getting two solids to react with each other is slow.

6. Factors that Affect Rate l Catalysts- substances that speed up a reaction without being used up.(enzyme). – Speeds up reaction by giving the reaction a new path. – The new path has a lower activation energy. – More molecules have this energy. – The reaction goes faster. l Inhibitor- a substance that blocks a catalyst.

7. Potential Energy Diagrams l Represent the changes in potential energy that occur during a chemical reaction. l The reaction coordinate represents the progress of the reaction.

8. Remember in terms of energy content l HIGH ENERGY =UNSTABLE l LOW ENERGY = STABLE

9. Classification of reactions l Exothermic Rx: releases energy. Heat part of the products. l Endothermic Rx: absorbs energy. Heat part of the reactants.

10. Definitions l Activation Energy: the minimum amount of energy needed to start up a chemical reaction. l l Activated Complex: a temporary intermediate product. Highest point of the diagram. Is UNSTABLE. l

11. Catalyzed Reactions l Need less energy to start up the reaction. The presence of a catalyst LOWERS THE ACTIVATION ENERGY!!!

12. Energy Reaction coordinate Reactants Products

13. Energy Reaction coordinate Reactants Products Activation Energy - Minimum energy to make the reaction happen

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

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

16. Thermochemistry The study of the changes in heat energy that accompany chemical reactions and physical changes.

17. What is  H?  H is the enthalpy, or “heat of reaction.” The amount of energy released or absorbed during a chemical reaction. By convention  H rxn = H products - H reactants

18. What is an exothermic reaction? A reaction that gives off or releases heat. Since...  H rxn = H products - H reactants then  H rxn will be a negative number

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

20. What is an endothermic reaction? A reaction that absorbs heat. Since…  H rxn = H products – H reactants then  H will be a positive number.

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

22. Heats of Reaction Table I The new reference table (Table I) shows different heats of reaction for some common reactions.

23. EXOTHERMIC RX l Release heat.  H for reaction is negative The value for  H is the amount of heat released during the rx l We write the heat it as PRODUCT in the chemical equation The greater the magnitude of  H the more stable the product will be!!!!

24. l Absorb heat  H for reaction is positive The value for  H is the amount of heat absorbed during the rx l We write the heat it as REACTANT in the chemical equation The greater the magnitude of  H the more UNstable the product will be!!!! ENDOTHERMIC RX

25. PAGE 140 ANSWERS RB 2012 edition 11. 4 12. 2 13. 1 14. 2 15. 2 16. 1 17. 3

26. INTERPRETING REACTION COORDINATES handout 1) B 2) A 3) G 4) G 5) A 6) F 7) F 8) F 9) F 10) B 11) E 12) I 13) D 14) J 15) C 16) H 17) H 18) A

27. PE DIAGRAMS FOR RX 1. EXO 2. -30 3. 20 4. 10 5. 60 6. ENDO 7. 25 8. 20 9. 30 10. SAME 11. H 12. E 13. B 14. G 15. I 16. F 17. A 18. C 19. D

28. HEATS OF REACTION MC 1) 1 2) 1 3) 4 4) 2 5) 2 6) 2 7) 2 8) 1 9) 1 10) 4 11) 4 12) 1