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Differential Rate Law

Differential Rate Law. Differential Rate Law. Deals with dependence of rate on… concentration. The important question. How will the rate of reaction change if we change the concentration of our reactants?. A simple example. Reaction A --> P. Method of initial rates.

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Differential Rate Law

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  1. Differential Rate Law

  2. Differential Rate Law • Deals with dependence of rate on… • concentration

  3. The important question • How will the rate of reaction change if we change the concentration of our reactants?

  4. A simple example • Reaction • A --> P

  5. Method of initial rates • Where we look at the initial rates (=[A]/t) • The measurement is taken as close to t=0 as possible

  6. [A]o 0.35 0.70 1.05 Initial Rate 7.20 x 10-4 2.90 x 10-3 6.45 x 10-3 Data

  7. The relationship • 2:4 • 3:9 • Rate depends on the square of the conc...

  8. So • Rate = k[A]2 • k= rate constant • To solve for k, sub in several values of rate with [A] and average

  9. Rate constant • While the rate is not constant • The rate constant is constant for a particular rxn at a particular temp.

  10. Using this information • What would the rate of rxn for A be if [A] = .16 M?

  11. A harder problem • A + B --> products • want to determine the rate law for the decomposition of “A” that takes into account [A] and [B]

  12. We know that... • Rate = -[A]/t • Rate = k[A]n[B]p • Goal is to find k, n, and p.

  13. Look at some data... • KEY- determine how the rate varies with varying concentration of one component while the concentration of the other is held constant

  14. We need k • Plug in values from a data set • (best way is to average k’s from all data sets!)

  15. Double Check • Plug in values from one set of data and see if you get observed rate.

  16. Overall order • The sum of the coefficients...

  17. Homework

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