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How can I control the rate of my Reactions?

Chemical Kinetics Chapter 15. How can I control the rate of my Reactions?. Kinetics. Study of speed or rate of reactions. Chemical Kinetics. We can use thermodynamics to tell if a reaction is product or reactant favored .

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How can I control the rate of my Reactions?

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

  2. Kinetics • Study of speed or rate of reactions.

  3. Chemical Kinetics • 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 Rates Section 15.1 • Reaction rate = change in concentration of a reactant or product with time. • Three “types” of rates • initial rate • average rate • instantaneous rate

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

  6. CALCULATING RATE

  7. RATE CALCULATIONS • 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 $150 70 days 30 days $5/day $2/day Mary

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

  9. Determining a Reaction Rate 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

  10. REACTION RATES RR =D [P ] = -D [R ] D t D t P =products R = reactants

  11. Relative Rates Reactant 2A g 4B + C - D [A ] = D [B ] = D [C ] 2D t 4D t D t

  12. Rate Expressions

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

  14. 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.

  15. COLLISION THEORY • C = collisions • E = energy • O = orientation

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

  17. Nature of Reactants • What you use

  18. Nature of Reactants Examples • Packaging materials • Food • Building materials • Clothing • Fireworks

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

  20. Concentration (M)amount present lower concentration of reactants More concentrated

  21. Concentration (M)amount present • Examples • Hydrogen peroxide • Food: vacuum packed • Breathing • Firemen

  22. Concentrations 0.3 M HCl 6.0 M HCl

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

  24. Physical state of reactant or Surface area

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

  26. SURFACE AREAamount in contact • Examples • Fire: solid / liquid fuels • Food: chew or grinding • Brewing: tea or coffee • Grain elevator

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

  28. Temperature • Increased temperature causes increased motion. • Increases the KINETIC energy

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

  30. Temperature Cold Hot D9 C30

  31. Temperature • Temperature is related to KineticEnergy Lower T has less E • T: related to motion Lower T = less motion Collide less

  32. Collision Theory NO Collisions Collisions Energy NO Collisions YES Energy Orientation

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

  34. Activation Energy • Energy needed to start reaction

  35. Energy Diagram

  36. Catalyzed Reactions d9 c23

  37. Hydrogen peroxide Rxt. C34

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

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

  40. Energy Diagram Ea Inhibitors

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