Kinetics

1. Kinetics Chapter 12 Chemistry SC5

2. Think About It • Rank in order from slowest to fastest chance of causing an automobile accident. • Option A: A person obeying all the traffic laws • Option B: A person changing the radio station in the car. • Option C: A person changing the radio station and making a phone call in the car. • Option D: A person changing the radio station, making a phone call and drinking water.

3. What Is a Reaction Rate? • Measures the change in concentration of a substance over time. • Concentration: moles in a liter (M) • Concentration of A is written as [A] • Units: mol/L x s

4. What Is the Formula of Average Rate? • Average Rate = Δ [reactant] / Δ time • Average Rate = concentrationfinal – concentrationinitial • timefinal – timeinitial

5. Practice 1 Average Rate • What is the average rate in a reaction between butyl chloride (C4H9Cl) and water, if the concentration of C4H9Cl is 0.220 M at the beginning and after 4.00 s the concentration of C4H9Cl is 0.100 M?

6. Practice Problems – Classwork/Homework Red Cards • P. 563 – Practice Problems • Problem 1 Black Cards • P. 563 – Practice Problems • Problem 2

7. Homework Chapter 16 • P. 586 #48 • Careful, go to moles!

8. Storyboarding Collision Theory • To understand reactions you have to be able to ‘see’ it at the molecular level. Picture it and all the theories make sense. • Activity: You are being given a colorful sheet of paper. You will storyboard the Collision Theory as it appears p. 563-565 in textbook. • Requirements: • Must have all three postulates. • Must have original wording of the postulate. • Must have your interpretation of the each postulate. • Must have a visual representation of each postulate. • Must have a summary box on its own (sentence combining).

9. Storyboarding Collision Theory • Rubric: • Requirements: • Must have all three postulates. _____/10 • Must have original wording of the postulate. ___/10 • Must have your interpretation of the each postulate. ___/10 • Must have a visual representation of each postulate. ___/10 • Must have a summary box on its own (sentence combining). ___/10 • Verbal Explanation ____/30 • Visually Pleasing ____/10 • Neatness/Colorful ____/10 • Total = ____/100 • Plagiarism from the book is a grade of 0 and you will have to redo.

10. ABC of Collision TheoryMy Storyboard • All three of these postulates affect the rate of the reaction because the reactants have to • Attack each other hard (correct energy) • Be aligned properly (hit on correctside) • Collide (findeach other)

11. Storyboarding Collision Theory • Rubric: • Requirements: • Must have all three postulates. _____/10 • Must have original wording of the postulate. ___/10 • Must have your interpretation of the each postulate. ___/10 • Must have a visual representation of each postulate. ___/10 • Must have a summary box on its own (sentence combining). ___/10 • Verbal Explanation ____/30 • Visually Pleasing ____/10 • Neatness/Colorful ____/10 • Total = ____/100 • Plagiarism from the book is a grade of 0 and you will have to redo.

12. Collision Theory • Collision • For a reaction to occur they reactants must collide.

13. Collision Theory • Activation Energy • For a reaction to occur you must have sufficient energy.

14. Collision Theory • Orientation • For a reaction to occur, you must have correct alignment.

15. Collision Theory • Youtube: Collision Theory • http://www.youtube.com/watch?v=xswUKlUSsc0 • Collision • Activation Energy • Orientation

16. Going Further with Collision Theory Homework • P. 586 (52, 54, 55) • Apply collision theory to explain why the increasing concentration of a reactant usually increases the reaction rate. • Food Preservation Apply collision theory to explain why foods usually spoil more slowly when refrigerated than at room temperature. • Apply collision theory to explain why powdered zinc reacts to form hydrogen gas faster than large pieces of zinc when both are placed in hydrochloric acid solution.

17. Factors Affecting Reaction Rates • A reaction can increase in rate (speed) or decrease in speed only by these factors. • Catalyst • Concentration • Nature of the reactant • Pressure • Surface Area • Temperature • That means stirring does NOT increase the rate of the reaction.

18. Factors Affecting Reaction Rates • Nature of the reactant • Is the reactant naturally reactive? • More unstable the more reactive it is. • Cs and F are very reactive. • Decreases activation energy which makes forming the activated complex easier.

19. Energy Products Reactants Reaction Pathway Activation EnergyEa – get into the game! Type of reactant decreasesthe activation energy. before after

20. Factors Affecting Reaction Rates • Concentration • The more of the reactant present, the higher the number of collisions. • Particles bump more if there are more there.

21. Factors Affecting Reaction Rates • Surface Area • The more parts the reactant can collide with the higher the reaction rate. • This increases the amount of collisions.

22. Factors Affecting Reaction Rates • Temperature • The higher the temperature, the faster the particles move which increase the number of collisions. • This increases collisions, good orientation and gives a higher energy.

23. Reaction Rates - Demonstration • H2O2 will decompose over time. 2 H2O2  2 H2O + O2

24. Reaction Rates - Demonstration Group As • You have a cup of hydrogen peroxide that is decomposing, observe the reaction and explain what you observe. • THINK: are there bubbles, is there a smell, does anything change, how long does it take, identify the product. • What can make this reaction go faster?

25. Reaction Rates - Demonstration Group Bs • You have a cup of hydrogen peroxide that is decomposing, observe the reaction and explain what you observe. • THINK: are there bubbles, is there a smell, does anything change, how long does it take, identify the product. • Identify if the yeast is a reactantor catalyst. • What is the difference between reactantand catalyst? • Why did the reaction occur so quickly?

26. Learning About Catalyst • What is the purpose of a catalyst in a reaction? • Does the catalyst react and form an new product? • To speed up a reaction by orienting the particles properly (glue) • A catalyst is just there to hold two pieces together, it does not form a new product.

27. Going Further with Collision Theory Homework • p. 586 (50, 51, 53, 56) • What role does reactivity of the reactants play in determining the rate of a chemical reaction? • In general, what is the relationship between reaction rate and reaction concentration? • Explain why a crushed solid reacts with a gas more quickly than a large chunk of the same solid. • Hydrogen peroxide decomposes to water and oxygen gas more rapidly when manganese dioxide is added. The manganese dioxide is not consumed in the reaction. Explain the role of manganese dioxide.

28. Activation Energy A major requirement for all REACTIONS to occur. Get over the ‘hump’ to form products

29. Energy Products Reactants Reaction Pathway Activation EnergyEa – get into the game! Type of reactant decreasesthe activation energy. before after

30. Reaction Pathway Activation EnergyEa – get into the game! Reaction Pathway – the direction of the reaction from the beginning to the end. Reaction from reactant to product.

31. Energy Reaction Pathway Activation EnergyEa – get into the game! Energy – how much energy is needed to complete the reaction. (q=mc(Tf - Ti)).

32. Energy Reactants Reaction Pathway Activation EnergyEa – get into the game! Just before the reaction begins, the energy needed to collide particles. Ea

33. Activated Complex Energy Reactants Reaction Pathway Activation EnergyEa – get into the game! The particles are colliding, aligned properly and finally hitting enough energy to form this intermediate. Ea

34. Activated Complex Energy Reactants Products Reaction Pathway Activation EnergyEa – get into the game! If the product is below the reactant, energy is released. This is an exothermic reaction. Usually, exothermic reactions feel warm or do work. Ea -ΔE

35. Activated Complex Energy Products Reactants Reaction Pathway Activation EnergyEa – get into the game! If the product is above the reactant, energy is absorbed. This is an endothermic reaction. Usually, endothermic reactions feel cold or require work. Ea +ΔE

36. Let Them Eat Cake Pudding We are going to make three concentrations of puddings • Following the recipe but using HALF the ingredients (except batter). • Following the recipe exactly. • Following the recipe but using DOUBLE the ingredients (except batter) • Predict what you think will happen and WHY? Which factors will affect the rate of the reaction?

37. Formal Lab Write Up Due a week from today. Look over rubric

38. Rate Law • Because of the nature of the reactant, there is a way to formulate a mathematical expression based on reaction and the concentration of the reactants. aA bB • The rate law for the above BALANCED chemical reaction is Rate = k[A]m. • General rate law have a constant, k whose units change depending on the order. • Exponent m tells you how reactive the reactant is.

39. Rate Law - Practice • Use the reactants below to write the rate law: aA + bB cC • Answer: Remember, you don’t know the superscript so use a variable.

40. Rate Law - Practice • Use the reactants below to write the rate law: aAB + bB cC • Answer: Remember, you don’t know the superscript so use a variable.

41. Zero Order • If the concentration of a reactant doubles but the rate does nothing, the reaction is zero order. • Write the rate law as Rate = k[B]0 Rate = k x 1 Rate = k

42. Practice Rate Law 1 • What happen to the [A]? • A. did not change B. doubled C. I don’t know • What happen to the rate? • A. did not change B. doubled C. I don’t know • What order is this reaction?

43. First Order Reactant • A reaction is first order if the concentration of ONE reactant doubles and the rate doubles. • Write the law as • Rate = k[A]1 • Rate = k[A] • k is just a constant that can be solved (unit is 1/s or s-1). • m = 1 to reflect the ‘1st’ order.

44. Practice Rate Law 1 • What happen to the [B]? • A. did not change B. doubled C. I don’t know • What happen to the rate? • A. did not change B. doubled C. I don’t know • What order is this reaction?

45. Combine Rate Laws • The overall order of reactionis: • The sum of the exponents in the rate law. • For example • Rate = k[A]0[B]1 • The overall reaction of the above is first order (0+1 = 1).

46. Overall Rate Law Problem 1: • NH4+ (aq) + NO2- (aq)  N2 (g) + 2 H2O (l) • Find the rate law

47. Problem 1: Answers • NH4+ (aq) + NO2- (aq)  N2 (g) + 2 H2O (l) • [NH4+] doubles; Rate doubles = first order • [NO2-] doubles; Rate doubles = first order • Rate Law: Rate = k[NH4+][NO2-]

48. Homework Homework, read the section 16.3. • Write down keywords you don’t understand. • Write down questions you had on the reading. • Write down questions you have on the math. • Problems p. 587 #66 (try #67)

49. Rate Determining Steps • To calculate the rate, you must look at the SLOWEST step. Label it as the rate determining step. • Ex 1: 2A  product (slow) • Rate = k[A]2 • Ex 2: 2A + B  product (slow) • Rate = k[A]2[B]

50. Which Is the Rate determining Step? • Step 1: O3 + NO  NO2 + O2 (slow) • Step 2: NO2 + O  NO + O2 (fast) Step 1