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Lecture 33

Lecture 33. Kinetics-2 13.4-13.6; 13.11; 13.14 1-December Assigned HW 13.22, 13.24, 13.26 , 13.34, 13.36, 13.58 , 13.62 Due: Monday 6-Dec. Concentration vs. Time – 0 th Order. a A. Products. The rate of 0 th order reactions are independent of concentration.

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Lecture 33

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  1. Lecture 33 Kinetics-2 13.4-13.6; 13.11; 13.14 1-December Assigned HW 13.22, 13.24, 13.26, 13.34, 13.36, 13.58, 13.62 Due: Monday 6-Dec

  2. Concentration vs. Time – 0th Order aA Products The rate of 0th order reactions are independent of concentration Decreasing Concentration Since the reaction rate does NOT change as [A] changes, [A] decreases linearly. [A] Slope = k Time 

  3. Concentration vs. Time – 1st Order aA Products The rate of 1st order reactions are dependent on concentration Rate 1 Rate 2 As [A] decreases, the rate decreases Reaction Rate Rate 3 Rate 1 > Rate 2 > Rate 3

  4. Integrated Rate Law - st Order aA Products

  5. Sample Problem A Products How long does it take for the concentration of A to decrease to 1.0% of its initial value in a the reaction (k = 1.0 Ms-1) Determine the order of the reaction. Use to solve for time.

  6. Sample Problem A Products How long does it take for the concentration of A to decrease to 1.0% of its initial value in a the reaction (k = 1.0 s-1) Determine the order of the reaction. Use to solve for time.

  7. Half Life for a 1st Order Reaction A Products How long does it take for the concentration of A to decrease to 50.0% of its initial value in a first order reaction. For a first order reaction, the time it takes for half of the reactants to decompose to products The half life is INDEPENDENT of CONCENTRATION for a 1st order reaction

  8. Half Life for a 1st Order Reaction A Products Each t1/2 is the same for 1st order reactions.

  9. Half Life for a 1st Order Reaction A Products The half life is ONLY dependent on k for a 1st order reaction

  10. Half Life for a 1st Order Reaction For the reaction: C2H6 2 CH3 k = 5.5 x 10-4 s-1 How long will it take for [C2H6] to fall to 1/16th it’s original concentration?

  11. Half Life for a 1st Order Reaction For the reaction: C2H6 2 CH3 k = 5.5 x 10-4 s-1 Calculate how long it will take for 1.5 M CH3 to be produced if the reaction begins with 1 M C2H6.

  12. Concentration vs. Time – 2nd Order aA Products The rate of 2nd order reactions are dependent on concentration Bigger k  faster rate

  13. Integrated Rate Law – 2nd Order aA Products A couple math steps

  14. Integrated Rate Law Summary 2nd Order 0th Order 1st Order Rate Law Integrated Rate Law

  15. Rates and Temperature – the link to Thermodynamics Arrhenius Equation Arrhenius parameters: Temperature independent A  pre-exponential factor Ea  activation energy Y-int = lnA Slope = -Ea/R

  16. Rates and Temperature – the link to Thermodynamics Arrhenius Equation The rate constant for the decomposition of N2O5 at 45 °C is k = 5.1 x 10-4 s-1. Determine the value of the rate constant at 50 °C if the activation energy is 103 kJ mol-1.

  17. Rates and Temperature – the link to Thermodynamics Arrhenius Equation Arrhenius parameters: Temperature independent A  pre-exponential factor Ea  activation energy The reverse reaction has a much larger Energy Barrier (Ea)

  18. Activation Energy and Catalysis

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