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Chemical Kinetics

Chemical Kinetics. The area of chemistry that concerns reaction rates and reaction mechanisms. Reaction Rate. The change in concentration of a reactant or product per unit of time. Rate Laws.

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Chemical Kinetics

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  1. Chemical Kinetics The area of chemistry that concerns reaction rates and reaction mechanisms.

  2. Reaction Rate The change in concentration of a reactant or product per unit of time

  3. Rate Laws Differential rate laws express (reveal) the relationship between the concentration of reactants and the rate of the reaction. The differential rate law is usually just called “the rate law.” Integrated rate laws express (reveal) the relationship between concentration of reactants and time

  4. Determining Order withConcentration vs. Time data (the Integrated Rate Law) Zero Order: First Order: Second Order:

  5. Solving an Integrated Rate Law Problem: Find the integrated rate law and the value for the rate constant, k A graphing calculator with linear regression analysis greatly simplifies this process!! (Click here to download my Rate Laws program for theTi-83 and Ti-84)

  6. Time vs. [H2O2] Regression results: y = ax + b a = -2.64 x 10-4 b = 0.841 r2 = 0.8891 r = -0.9429

  7. Time vs. ln[H2O2] Regression results: y = ax + b a = -8.35 x 10-4 b = -.005 r2 = 0.99978 r = -0.9999

  8. Time vs. 1/[H2O2] Regression results: y = ax + b a = 0.00460 b = -0.847 r2 = 0.8723 r = 0.9340

  9. And the winner is… Time vs. ln[H2O2] 1. As a result, the reaction is 1st order 2. The (differential) rate law is: 3. The integrated rate law is: 4. But…what is the rate constant, k ?

  10. Finding the Rate Constant, k Method #1: Calculate the slope from the Time vs. ln[H2O2] table. Now remember:  k = -slope k = 8.32 x 10-4s-1

  11. Finding the Rate Constant, k Method #2: Obtain k from the linear regresssion analysis. Regression results: y = ax + b a = -8.35 x 10-4 b = -.005 r2 = 0.99978 r = -0.9999 Now remember:  k = -slope k = 8.35 x 10-4s-1

  12. Rate Laws Summary

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