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Controlling Reaction Rates: Chemical Kinetics Guide

Understand how to control the speed of reactions through factors like reactant concentration, temperature, and catalysts in this comprehensive study of chemical kinetics. Learn about reaction rates, collision theory, and the influence of nature of reactants.

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Controlling Reaction Rates: Chemical Kinetics Guide

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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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