1. How can I control the rate of my Reactions? Chemical Kinetics Chapter 15

2. Kinetics Study of speed or rate of reactions.

3.  We can use thermodynamics to tell if a reaction is product or reactant favored.  But this gives us no info on HOW FAST reaction goes from reactants to products.  KINETICS — the study of REACTION RATES and their relation to the way the reaction proceeds, i.e., its MECHANISM.  The reaction mechanism is our goal!  We can use thermodynamics to tell if a reaction is product or reactant favored.  But this gives us no info on HOW FAST reaction goes from reactants to products.  KINETICS — the study of REACTION RATES and their relation to the way the reaction proceeds, i.e., its MECHANISM.  The reaction mechanism is our goal!

4.  Reaction rate = change in concentration of a reactant or product with time.  Three “types” of rates  initial rate  average rate  instantaneous rate Reaction Rates Section 15.1

5. What is similar ? ratio of two things TIME always Bottom !!!!! Rate =  [ x ]  t Change in amount Change in time

6. CALCULATING RATE

7. RATE CALCULATIONS 1.John takes 10 weeks to earn $150. However, Mary earns $150 in 30 days. Calculate the rate at which they both earn money. Which has the larger rate? Mary John Amount Amount Time Time Rate ($/day) Rate ($/day) Larger = $150 30 days 70 days $5/day$2/day Mary

8. REACTION RATES ! ! RR =  [reactants ]  t RR =  [products ]  t

9. Blue dye is oxidized with bleach. Its concentration decreases with time. The rate — the change in dye conc with time — can be determined from the plot. Blue dye is oxidized with bleach. Its concentration decreases with time. The rate — the change in dye conc with time — can be determined from the plot. Dye Concentration

11. REACTION RATES RR =  [P ] = -  [R ]  t  t P = products R = reactants

12. Relative Rates Reactant 2A  4B + C -  [A ] =  [ B ] =  [ C ] 2  t 4  t  t

13. Rate Expressions

14. HOW CAN WE CHANGE REACTION RATES ? Some reactions need to be fast : airbags. Some reactions are slowed ; time released pills Examples:

15. Collision Theory D9 C20 (theory about molecules colliding) Rate of reactions depend molecules colliding in such a way that old bonds break and new bonds form.

16. COLLISION THEORY C = collisions E = energy O = orientation

17. Factors Affecting RXN Rates Nature of Reactants Temperature Concentration Surface Area/ Physical state Catalysts

18. Nature of Reactants What you use

19. Nature of Reactants Examples Packaging materials Food Building materials Clothing Fireworks

20. Nature of Reactants The materials used Activation Energy; Unique to each substance Orientation of reactants; depends on reactants

21. lower concentration of reactantsMore concentrated Concentration (M) amount present

22. Examples Hydrogen peroxide Food: vacuum packed Breathing Firemen

23. 0.3 M HCl 6.0 M HCl Concentrations

24. Concentration (M) amount present Increasing the number of reactants, the chance of successful Collisions increase.

25. Physical state of reactant or Surface area

26. Surface Area More it can be spread out  more area Paper (demo) MORE kindle ground LESS Whole bean Logs  

27. SURFACE AREA amount in contact Examples Fire: solid / liquid fuels Food: chew or grinding Brewing: tea or coffee Grain elevator

28. Surface Area Number of particles that are exposed. More surface area = more reactions More contact = more Collisions.

29. Temperature Increased temperature causes increased motion. Increases the KINETIC energy

30. TEMPERATURE Examples Glowstick Cook / freeze Summer / winter Ice pack / hot packs Medication

31. Temperature Cold Hot D9 C30

32. Temperature Temperature is related to Kinetic Energy Lower T has less E T: related to motion Lower T = less motion Collide less

33. Collision Theory Collisions Energy Collisions Energy Orientation NO YES

34. Catalyst / Inhibitors A substance NOT permanently changed during the reaction. Changes energy needed to start reaction

35. Activation Energy Energy needed to start reaction

36. Energy Diagram

37. Catalyzed Reactions d9 c23

38. Hydrogen peroxide Rxt. C34

39. Catalyst Works by changing the activation energy required The lower the Ea the greater the rate of the reaction.

41. Inhibitors d9 c38 Works by changing the activation energy required The greater the Ea the lower the rate of the reaction.

42. Energy Diagram Inhibitors Ea