Reaction Rates (Kinetics)

1. Reaction Rates (Kinetics) Chapter 16

2. Big Picture Thermodynamics (energy) tells us in which direction a change occurs e.g. does a ball roll up or down a ramp? Kinetics (reaction rates) tells us how fast a change occurs e.g. what is the speed of the ball rolling down a ramp?

3. Next Generation Science Standard Kinetics: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperatureor concentration of the reacting particles on the rate at which a reaction occurs.

4. Next Generation Science Standard Equilibrium Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.

5. ‘Rate’ Defined Rate = how quickly or slowly a change occurs Rate = change per unit of time e.g. Slow test taker: 1 question per minute Fast test taker: 2 questions per minute

6. Rate UnitsThink about it….. Which unit is used to express a car’s rate of motion down the road in: • USA • Mexico

7. Pre-Physics VELOCITY EQUATION:   velocity = distance          OR        v =  d   time t What is the speed of a baseball that travels 49 meters in 2.4 seconds? ANS = 20 m/s

8. Pre-Physics        v =  d                  t Rearrange the equation for velocity into its two other algebraic forms. How long will your trip take (in hours) if you travel 350 km at an average speed of 80 km/hr? ANS = 4.4 hours

9. Rate Real world example eggs + flour cupcakes The rate of baking can be measured by: • How quickly the eggs are used up, OR • How quickly the flour is used up, OR • How quickly the cupcakes are made.

10. Some reactions occur very slowly: E.g. rusting of iron Some reactions occur very rapidly: E.g. explosion of TNT Chemical Reaction rates

11. Reaction Rate A  B + C • Reactant = A(ingredients) • Products = B & C (what is produced) • Reaction Rate = Δ[C] Δt • Delta, Δ= Change • [C] = concentration of C

12. Reaction Rates Graph Think about it….. What is this graph telling us about reaction rate?

13. In this graph: Which line is the reactant? Which lines are the product(s)? How do we know? Read p. 580 para 1 Graph: think about it……. N2O5 NO2 + O2

14. Concentration vs Time graph • What happens to concentration as a reaction progresses? Reactant decreases. (negative slope) Product increases. (positive slope) 2N2O5 4NO2 + O2

15. Conc vs Time graph: p. 580 fig 3 • What does the slope of each line tell us? Slope = rise (y) over run (x) Slope = Reaction rate!! Read para 3 2N2O5 4NO2 + O2

16. Does the slope stay the same the entire time? No. How does the slope change over time? What does that tell us? The slope starts out steep…. meaning that the reaction starts out fast Over time, the slope becomes more flat meaning that the reaction slows down Conc vs. Time graph (consider the blue line) 2N2O5 4NO2 + O2

17. Do all the lines have the same slope? No Why is the slope of the red line steeper than the slope of the blue line? Read p. 580 para 2 Reaction rate 2N2O5 4NO2 + O2

18. Free Write (closed notes) Reaction Rates Can Be Represented Graphically Write a paragraph describing what a concentration vs time graph can tell us about reaction rates

19. Think about it…. Model: Reaction rates can be explained by thinking at the particle level PhET: Reactions and Rates

20. Molecular Collision At the particle level, in order for a chemical reaction to happen, a collision between reactant molecules must occur Teacher Notes: PhET Reactions and Rates

21. Collisions Notes: For a reaction to occur, reactant particles must collide with: • correct orientation • sufficient energy YouTube: How to speed up chemical reactions (and get a date) -

22. How can the rate of a chemical reaction be increased? Students know how reaction rates depend on such factors as: • concentration • temperature • pressure

23. Chemical Engineer = $$$$$$$$$$ 2012 Median Pay $94,350 per year $45.36 per hour Design chemical plant equipment and devise processes for manufacturing chemicals and products, such as gasoline, synthetic rubber, plastics, detergents, cement, paper, and pulp, by applying principles and technology of chemistry, physics, and engineering.

24. What factors effect the rate of a reaction? Notes 1. Temperature: Increase T increase rxn rate. WHY? • particles collide more often • particles collide with more energy

25. What factors effect the rate of a reaction? 2. Concentration: Increase the amount of reactant  increase rxn rate. WHY? • particles collide more frequently (more “crowding”)

26. What factors effect the rate of a reaction? 3. Pressure: (effects reaction rate in the gas phase only) • increase pressure = increase reaction rate

27. Think about it….. • With your neighbor, discuss what an enzyme is / does (think back to biology last year). Write a definition for the word enzyme in your notes. (textbooks closed)

28. 16.2 Think about it…. The combustion of a piece of coal is exothermic. Yet a piece of coal does not just spontaneously catch fire? WHY?

29. Activation Energy, EA

30. Standard 8d * Students know the definition and role of activationenergy in a chemical reaction. Read p. 590 para 1-3 Read p. 590 para 4-5

31. Catalysts Frayer: Definition/Facts/ Diagram/Examples p. 593-595 Not a list of cats

32. Frayer: Catalyst Definition: • Unasubstanciaquecambialatasadeunareaccionquimicasinsercounsumidanicambiarsignificativamente • Asubstancethatchangestherateofachemicalreactionwithoutbeingconsumed • A substance that changes the rate of a chemical reaction without being consumed YouTube:Whatare catalysts? | Chemistry for All | The Fuse School

33. Catalysts Facts(p. 593-595): • Only a small amount required • Is not used up in the reaction • Provides a different pathway from reactant to product with a lower activation energy

34. Catalysis: Diagram

35. Think about it…. Activation Energy. Study figure 9 on p. 591. What are these diagrams telling us? What are the similarities and differences between figure 9a and 9b?

36. 16.2 Reaction Pathways: Hess’s Law* What makes a reaction exothermic? 2HI  H2 + I2 Energy of rxn = - 52 KJ/mol • Bond breaking absorbs energy (endothermic) • Energy to break H-I bond • Bond forming releases energy (exothermic) • Energy to form new H-H bond and new I-I bond • Energy released > energy absorbed • Overall rxn releases energy (exothermic)

37. Catalyst Examples Haber Process nitrogen + hydrogen  ammonia (NH3) Catalyst = iron

38. Catalyst Examples:Catalytic Converter

39. Catalyst Examples Decomposition of hydrogen peroxide: H2O2  H2O + O2 Catalyst = potassium iodide OR manganese dioxide Teacher notes: “elephant toothpaste”

40. Catalysts Subset: Enzymes • biological catalysts • Made of protein e.g. lactose • Catalyzes the metabolism of lactase (milk sugar) • DNA polymerase

41. 16.2 Catalysts Enzymes work by the “Lock and Key mechanism” Teacher notes: Youtube - Enzyme Function (University of Surrey)

42. Master Degree: University of Arizona 1994-97 Enzyme: Sulfite Oxidase Metabolizes sulfur in liver: Sulfite  Sulfate Metalloenzyme: protein containing molybdenum and iron Catalyst: Examples

43. Inhibitors • An inhibitor is something that slows down or stops a reaction.