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Outline: 2/7/07

Outline: 2/7/07. Extra Seminar – today @ 4pm Exam 1 – one week from Friday…. Outline Chapter 15 - Kinetics (cont’d): - integrated rate law calcs = Half-life calcs - Arrhenius Rate equation. Variation on a theme: Half-life. Radioactive decay = 1 st order decay

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Outline: 2/7/07

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  1. Outline: 2/7/07 • Extra Seminar – today @ 4pm • Exam 1 – one week from Friday… • Outline • Chapter 15 - Kinetics (cont’d): • - integrated rate law calcs • = Half-life calcs • - Arrhenius Rate equation

  2. Variation on a theme: Half-life • Radioactive decay = 1st order decay • Integrated rate law: ln(At/Ao) = -kt • In the case that At = 0.5 Ao • (half is left) • t = t1/2 • therefore: ln(0.5) = - kt1/2 • half-life is just another way to define the rate constant k.

  3. Radiation Biology (131I): Time (days) 0 3 6 9 12 Mass 131I (mg) 12 9.25 7.14 5.50 4.24 What is the half-life of 131I? Half-life example ln(At/Ao) = -kt ln(7.14/12)= - k (6 days) k = 0.0865 day-1 ln(1/2) = -kt1/2 -0.693 = - .0865 (t1/2) t1/2 = 8.0 day

  4. Half-life example Given t1/2 of 22.3 years for 210Pb, and 10,000 atoms deposited on top of the lake sediment in 1905, how much 210Pb left now? ln(At/Ao) = -kt ln(1/2)= - k (22.3 yr) k = 0.0311 yr-1 ln(A100/10000) = - 0.0311 yr-1 (100 yr) A100/10000 = exp(- 3.11) A100 = 446 atoms

  5. Summary of Chapter 15 so far: • Rates depend upon concentrations of the species involved. • There is a relationship between number of species involved and rate of reaction (e.g. unimolecular, bimolecular…) • Can build a rate law from observed data: Rate = k [A]m[B]n • m, n depend only on the chemical reaction under consideration….

  6. Summary of Chapter 15 so far: • Can use integrated rate laws to predict rates of reaction, concentrations at various times, etc.e.g.half-life • Can use empirical data to determine rate law.

  7. Let’s try some keypad questions…

  8. Determine the rate law for the reaction:2ClO2(aq) + 2 OH-(aq) ClO3-(aq) + ClO2-(aq) + H2O(l)Experiment[ClO2] [OH-] Initial Rate of rxn1 0.12M 0.12M 2.07 x 10-4 M/s 2 0.12M 0.24M 8.28 x 10-4 M/s 3 0.24M 0.24M 1.66 x 10-3 M/s • Rate = k [ClO2]2[OH-]2 • Rate = k [ClO2][OH-]2 • Rate = k [ClO2]2[OH-] • Rate = k [ClO2][OH-]

  9. Determine the value of the rate constant for:2ClO2(aq) + 2 OH-(aq) ClO3-(aq) + ClO2-(aq) + H2O(l)Experiment[ClO2] [OH-] Initial Rate of rxn1 0.12M 0.12M 2.07 x 10-4 M/s 2 0.12M 0.24M 8.28 x 10-4 M/s 3 0.24M 0.24M 1.66 x 10-3 M/s • k = 0.0144 M-1 s-1 • k = 0.0144 M-2 s-1 • k = 0.120 M-1 s-1 • k = 0.120 M-2 s-1 • None of the above

  10. k also depends on temperature and Arrhenius Activation energy…. • DEMO

  11. k also depends on temperature and Arrhenius Activation energy…. 15-6 • k = A e -Ea/RT • k = Rate law constant • A = constant (frequency factor) • Ea = Arrhenius Activation Energy • R = 8.315 J/mol K • T = Temperature

  12. e.g. big Ea • e - (big) • = small k = small rate! • What does Ea mean in terms of rate? • k = A e -Ea/RT • e.g. small Ea • e - (small) • = big k = big rate!

  13. Problems to try: Chapter 15 • 15.13, 15.17, 15.19, 15.21, 15.23, 15.25, 15.27, 15.29, 15.31, 15.33, 15.39, 15.45, 15.47, 15.51, 15.57, 15.59, 15.61, 15.63, 15.65, 15.67, 15.69, 15.73, 15.77, 15.81, 15.85, 15.87, 15.89, 15.91, 15.95, 15.103

  14. Practice Problems: Chapter 14 • 14.11, 14.15, 14.17, 14.19, 14.23, 14.25, 14.27, 14.31, 14.35, 14.37, 14.38, 14.41, 14.43, 14.49, 14.51, 14.53, 14.55, 14.57, 14.61, 14.65, 14.67, 14.71, 14.75, 14.77, 14.79, 14.81, 14.91, 14.101, 14.103

  15. Problems to try: Chapter 13 • 13.1, 13.3, 13.5, 13.7, 13.9, 13.11, 13.15, 13.19, 13.21, 13.35, 13.43, 13.45, 13.47, 13.49 Problems to try: Chapter 12 • 12.3, 12.5, 12.7, 12.9, 12.11, 12.17, 12.19, 12.29, 12.31, 12.33, 12.35, 12.39, 12.41, 12.43, 12.49, 12.51, 12.53, 12.55, 12.63

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