1. Reaction Rates Reaction Kinetics, Factors that Influence Rates, and Activation Energy

2. Standards 8. Chemical reaction rates depend on factors that influence the frequency of collision of reactant molecules. As a basis for understanding this concept: a. Students know the rate of reaction is the decrease in concentration of reactants or the increase in concentration of products with time. 8. b. Students know how reaction rates depend on such factors as concentration, temperature, and pressure. 8. c. Students know the role a catalyst plays in increasing the reaction rate. 8. d.* Students know the definition and role of activation energy in a chemical reaction.

5. Example Reaction #2 H 2 (g) + I 2 (g) 2 HI (g) hydrogen iodinehydrogen gas gas iodide +

6. Definitions r (reaction rate) –  how fast we use up a reactant  how fast we make a product 2A  AA chemical kinetics – the study of chemical reaction rates.

7. Definitions r (reaction rate) –  how fast we use up a reactant  how fast we make a product 2A  AA chemical kinetics – the study of chemical reaction rates.

8. Definitions r (reaction rate) –  how fast we use up a reactant  how fast we make a product 2A  AA chemical kinetics – the study of chemical reaction rates.

9. Factors that Affect Reaction Rates Temperature – More reactant molecules are moving fast enough Warm glowsticks glow brighter Chilled food spoils slower Concentration (pressure for gases) – Reactants are hitting each other more often Greater concentration = Faster reaction Lower concentration = Slower reaction Surface Area – Reactants are hitting each other more often Start bonfires with crumpled paper or small twigs Catalysts – They hold reactant molecules in an optimal orientation, which speeds up the reaction

10. Activation Energy Activation Energy (E A ) – The amount of energy reactants need to form the transition-state (the in-between) and the reaction to proceed. aka “the hurdle” the reactants need to get over.

11. Molecular Speed vs. Temperature Molecule Energy Number of Molecules EAEA 300K 400K

12. Looking at Reaction Energy Reaction Proceeds Energy Reactants Products EAEA exothermic reaction

13. Looking at Reaction Energy Reaction Proceeds Energy Reactants Products EAEA endothermic reaction

14. Looking at Reaction Energy Reaction Proceeds Energy Reactants Products EAEA With catalyst

15. Catalyst Catalyst – a substance not used up in a reaction that speeds up the reaction by lowering the activation energy, E A. A catalyst also holds onto one of the reactants and positions the reactant so that it is easier to hit in the critical spot. 2 H 2 O 2 (l) 2 H 2 O (g) + O 2 (g) I2I2

16. Transition State I – + CH 3 Cl CH 3 I + Cl – transition state aka activated complex

17. Transition State I – + CH 3 Cl Cl – + CH 3 I

18. Transition-State I – + CH 3 Cl Cl – + CH 3 I

19. Transition State I – + CH 3 Cl Cl – + CH 3 I

20. HCl (aq) + H 2 O (l) H 3 O + (aq) + Cl – (aq) hydro- waterhydronium chloride chloric acid ion ion + +

21. N 2 (g) + 3 H 2 (g) 2 NH 3 (g) + 92kJ nitrogen hydrogen ammoniaheat gas gas gas + +

22. Reaction Steps 2 N 2 O (g) 2 N 2 (g) + O 2 (g) N 2 O (g) N 2 (g) + O (g) (slow) N 2 O (g) + O (g) N 2 (g) + O 2 (g) (fast) + Overall Reaction rate-determining step

23. Reaction Steps 2 N 2 O (g) 2 N 2 (g) + O 2 (g) N 2 O (g) N 2 (g) + O (g) (slow) N 2 O (g) + O (g) N 2 (g) + O 2 (g) (fast) + 1212 transition-state intermediate reactants products

24. 1 st Order Rate Law The greater the concentration, [A], the greater the reaction rate. This is a first-order rate law because it is concentration, [A], to the power of 1. A B rate = k·[A] mol/L s 1

25. 1 st Order Rate Law Example At 660 Kelvin, the rate constant, k, equals 4.5 × 10 -2 s -1. What is the reaction rate when there is a concentration of 500,000 ppm? SO 2 Cl 2 (g) SO 2 (g) + Cl 2 (g) rate = k·[SO 2 ] 1 rate = ( 4.5 × 10 -2 )·[500,000] rate = 22,500 ppm/s

26. Other Order Rate Laws The reaction rate may increase with increasing concentrations of both reactants, [A] and [B]. The powers, x and y, may or may not relate to the coefficients on the balanced chemical equation. A + B C rate = k·[A] x ·[B] y

27. 2 N 2 O 5 (g) 2 NO 2 (g) + O 2 (g)

29. Ne F ONC B Be He Li H KrAr Cl Br Xe ISPSi Mg Al Ca Na K

30. Ne F ONC B Be He Li H KrAr Cl Br Xe ISPSi Mg Al Ca Na K

32. 4 e – in valence shell