Laws Order

							Slide 1      Section 12.2
      Rate Laws & Reaction Order

For this reaction:
          aA + bB  Products
• A and B are chemical formulas for the
  reactants
• a and b are the coefficients in the balanced
  equation


Rate Law expression= k[A]m [B]n
            How to determine
Slide 2        m and n
• For simple reactions (the ones found in this
  class) an exponent of 1 means that the rate
  depends linearly on the concentration of the
  corresponding reactant.
• For example if m=1 and the [A] is doubled, the
  rate doubles.
• If m = 2 and the [A] is doubled, [A]2 quadruples
  and the rate increases by a factor of 4.
• If m=0, the rate is independent of the [A]
Slide 3

The m and n that you put as exponents are
the rate orders for the reactants.

For the given reaction:
   Rate = k [ A]2 [B]

It is read as:
       The reaction is in the 2nd order for A, first
order for B and third order for the whole
reaction
Slide 5




                 Section 12.3
          Experimental Determination
                 Of Rate Law
Slide 6
 Let’s look at the following reaction:

 2NO(g) + O2(g)  2NO2(g)

 And the following experimental data
 Experiment   Initial [NO] Initial [O2]   Initial Rate
                                               M/s
          1      0.015         0.015          0.024
          2      0.030         0.015         0.096
          3      0.015         0.030         0.048
          4      0.030         0.030         0.192
Slide 7

 Analyzing the data you see that when the
 [NO] is doubled (comparing experiment 1 to
 2) and the [O2] stays the same, the rate
 increases by a factor of 4, telling you that
 [NO] is in the second order.


 And when the [O2] is doubled (comparing
 experiment 1 to 3) the rate doubled, from
 the initial rate, telling you that [O2] is in the
 first order.
Slide 4
                Units for the reaction:

Rate Law           Overall Rate     Units for k
                   Order

Rate = k[B]        First order      1/s


Rate = k [A]2      Second order     1/M(s)


Rate = k[A]2[B]    Third order      1/M2(s)