KINETICS AND EQUILIBRIUM

1. KINETICS AND EQUILIBRIUM

2. BELL RINGER How can you make a reaction occur quicker?

3. Kinetics - The study of reaction rates and their relation to the way the reaction proceeds, ie. its mechanism breaking A REACTION is the _________ and ____________ to make entirely new compounds as products re-forming

4. Reaction Mechanism Step by step process needed to make a product How to get from a  b Reactants  Products • Just like making a recipe! • Can’t omit steps • Can’t change the order of the steps • Can’t omit any reactants

5. Some Practice Determine if the following chemical reactions would be considered slow or fast: Rusting Alka Seltzer in water Styrofoam decomposing Weathering of rocks Bleaching fabric

6. What determines the rate of a reaction? 1. Number of steps more steps mean a slower rxn 2. Rate determining step = slowest step of the rxn - the MOST important factor in determining the rate A + B + C  ABC (2 steps) Tall hill Short hill

7. Collision Theory “You can’t react if you don’t collide!” Bumper cars – need to get bumped out of your seat – going fast enough

8. Collision Theory “You can’t react if you don’t collide!” 1. Proper orientation Side collisions just move you, need to hit head on for the bonds to be broken and new bonds be formed A2 + B2 2AB

9. Collision Theory “You can’t react if you don’t collide!” 2. Speed Particles need to have enough speed when they collide. They need that MINIMUMamount of energy Activation Energy Ea

10. Collision Theory Summary Successful collisions occur only when: 1. Particles collide with the correct orientation 2. Particles collide with enough speed Click here! Click here! CAR ACCIDENT CAR ACCIDENT #2 Motorcycle’s

11. Some Kinetics Terminology Kinetics How fast a reaction occurs and the mechanism by which it occurs Rate Velocity (speed) at which a reaction occurs

12. Activation Energy Ea Amount of energy needed to “kick-start” a reaction Example: A match will not light on its own, the match must have an addition of mechanical energy (striking the box) so it will light Demo: Balloon

13. You can make reactions go faster by changing… “Make more collisions” Temperature Concentration Particle Size Nature of Reactants Catalysts Pressure

14. You can make reactions go faster by… “Make more collisions”  Temperature Increase • Particles moving faster = more likely to collide • Increased speed = greater force of the collisions

15. You can make reactions go faster by… “Make more collisions” Concentration Increase • More particles = More collisions • “Crowded Space”

16. You can make reactions go faster by… “Make more collisions” Particle Size Also known as Surface Area Decrease Making the particles smaller, ↑ SA vs ↑ SA → increases chance for effective collisions

17. You can make reactions go faster by… “Make more collisions” Nature of Reactants Ionic are faster

18. You can make reactions go faster by… “Make more collisions” Catalysts Def – a substance that increases the rate of reaction without being used up It lower the Ea, lowers the activated complex, and/or reaction pathway is shortened Lower Ea Makes collisions easier to occur

19. You can make reactions go faster by… “Make more collisions” Pressure Increase (Only gases)

20. You can make reactions go faster by… “Make more collisions”       Increase Temperature Concentration Particle Size Nature of Reactants Catalysts Pressure Increase Decrease Ionic are faster Lower Ea Increase (Only gases)

21. Heat of Reaction ΔH The difference between the potential energy of the products and the potential energy of the reactants ΔH = Hproducts – Hreactants

22. PE (KJ) Reaction coordinate PE of activated complex Ea H PE of reactants PE of products PE of products Activated complex Occurs when reactants collide in the proper orientation Bonds are in the process of breaking and forming Very unstable, only lasts a moment Quickly moves to products

23. BELL RINGER ID the letters below:

24. Ea H PE of reactants PE (kJ) PE of products PE of products Reaction coordinate Ea with a catalyst Catalyst - Compound which lowers Ea Is not permanently changed in the reaction Can be reused Does not change the  H

25. ΔH is always + Endothermic ΔH = Hp - Hr ΔH = 300 - 100 = 200

26. ΔH is always - Exothermic ΔH = Hp - Hr ΔH = 50 - 150 = -100

27. Rate of Reaction #1

28. Rate of Reaction #2

29. BELL RINGER Given the following balanced equation: N2(g) + O2(g) + 182.6 kJ  2NO(g) Draw the potential energy diagram below. Potential Energy Reaction Coordinate

30. Explain this demonstration

31. PE (kJ) Reaction coordinate Reversible Reaction Some reactions can run back to reactants A+ B AB A + B AB Eaf Ear A+B H AB RVS FWD Reactions are opposite One is exothermic,one is endothermic! H is the same, but has opposite signs

32. Equilibrium The following conditions must be met: • Can only be reached in a closed system • Rate forward rxn = Rate reverse rxn • Concentration of each solution is constant • Saturated Solutions are at equilibrium

33. Equilibrium A. Establishing First only the forward reaction occurs A + B --> C There is no product to run the reverse reaction Click the mouse to watch the forward reaction begin forward forward B A B A B A B A BA B B A A A A A B A B B A A B A B A B C C forward C forward C Click to go to next scene

34. Equilibrium As the [products] increases, some products begin to change back to reactants C A + B This is the start of the reverse reaction forward forward B A B A B A B A BA B B A A A A A B A B B A A B A B A B C C forward Reverse C A B forward Reverse C A B Click to go on

35. Equilibrium Eventually, the RATE of the forward reaction equals the rate of the reverse reaction This is Dynamic Equilibrium Equilibrium - When the rate of the forward reaction is equal to the rate of the reverse reaction Concentration of products and reactants do not change Amount of products do not usually equal the amount of reactant forward forward Reverse Reverse B A B A B A B A BA B B A A A A A B A B B A A B A B A B C C A B A B forward forward Reverse C C A B forward C forward Reverse Did you notice that we always have the same amount of products and reactants? C A B Did you also notice that we have way more reactants than products? Click to go on

36. Equilibrium Review Equilibrium only occurs when the rate of the forward reaction equals the rate of the reverse reaction At equilibrium the amount of reactants do not equal the amount of products At equilibrium, the concentration of reactants and products do not change enough product has been created The reverse reaction only begins when

37. BELL RINGER What is the value for the activation energy? What is the heat of reaction?

38. Types of equilibriums (must be in closed systems) Physical Equilibrium: - involves a physical change a. Phase equilibrium – occurs during a phase change (s) ↔ (l) RATEof Melting = Rateof Freezing (l) ↔ (g) RATEof Evaporation = Rateof Condensation b. Solution equilibrium – at a solution’s saturation point RATE of dissolving = Rate of crystallization Example NaCl(s) ↔ NaCl(aq)

39. Types of equilibriums (must be in closed systems) Chemical Equilibrium: RATEof forward rxn = Rateof reverse rxn RATEof breaking bonds = Rateof forming bonds H2(g) + I2(g) + 53.0 kJ ↔ 2 HI(g) Notice the concentrations are not equal, but constant

40. LeChatelier’s Principle ‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’ How a system at equilibrium will respond to stress STRESS - any change in temperature, concentration, or pressure put on a system at equilibrium When a STRESS is added to a system at equilibrium, the system will shift in order to relieve that stress and reach a new equilibrium. SHIFT = An increase in the RATE of EITHER the forward OR reverse rxn

41. LeChatelier’s Principle ‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’ SHIFT = an increase in the RATE of EITHER the forward OR reverse rxn toward the products SHIFT TO RIGHT Rate of the FORWARD reaction INCREASES PRODUCTS REACTANTS toward the reactants SHIFT TO LEFT Rate of the REVERSE reaction INCREASES REACTANTS PRODUCTS

42. LeChatelier’s Principle ‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’ • General Ideas: • If a concentration, temperature, or gas pressure is increased, the reaction shifts away from the increase in order to use up the extra & re-establish equilibrium. • If a concentration, temperature, or gas pressure is decreased, the reaction shifts toward the decrease in order to replace what was removed & re-establish equilibrium. AA – what you ADD causes a shift AWAY TT– what you TAKE causes a shift TOWARDS

43. LeChatelier’s Principle ‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’ SIMULATION

44. LeChatelier’s Principle ‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’ Stress: Increased 2SO2(g) + O2(g)↔ 2SO3(g) + Heat Increase [SO2] Increase Temperature Increase Pressure

45. LeChatelier’s Principle ‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’ Stress: Decreased 2SO2(g) + O2(g) 2SO3(g) + Heat Decrease [SO2] Decrease Temperature Decrease Pressure

46. LeChatelier’s Principle ‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’ CoCl(H2O)5 + Cl- + Heat ↔ CoCl2(H2O)2 + 3H2O PINK BLUE favors endo- Shifts Right Warm Water Cold Water favors exo- Shifts Left favors reverse Add Water Shifts Left

47. BELL RINGER Given the following reaction: H2(g) + F2(g)  2 HF(g) + Heat In terms of LeChatelier’s, what could you do to increase the production of hydrogen fluoride?

48. Why do chemical/physical changes occur? ENTROPY (ΔS)–degree of randomness or chaos or disorder or “messiness” in a system - Nature tends to proceed to a state of greater entropy, or disorder The MORE order you have, the LESS entropy in your system The LESS order you have, the MORE entropy in your system

49. Why do chemical/physical changes occur? A phase change is the most significant factor in determining ΔS Increased entropy Changing from s  l  aq  g Draw particle diagrams for each below Entropy increases when a compound is broken down Entropy decreases when a compound is created and bonds are formed

50. Entropy Examples Which of the following would you expect to have a higher entropy?