Chemistry Kinetics

Question

A reaction is performed to study the reaction of nitrogen dioxide with carbon monoxide:

NO2 + CO --> NO + CO2

The following reaction rate data was obtained in four separate experiments.

Experiment	[NO2], M	[CO], M	Initial Rate, M s^-1
1	0.756	0.266	0.357
2	1.51	0.266	1.43
3	0.756	0.532	0.357
4	1.51	0.532	1.43

What is the rate law for the reaction and what is the numerical value of k?

Complete the rate law in the box below. Remember that an exponent of '1' is not shown and concentrations taken to the zero power do not appear.

(Use k for the rate constant.)

Rate =  

k=____ M^-1 s^-1

Answer 1

Answer 2

Use the data in the table to determine the order of reaction with respect to each reactant. Find 2 experiments where the concentration of one reactant remains constant, while the other changes. Compare how the rate changes to how the concentration changes. This will tell you the order with respect to that reactant.

For NO₂, compare experiments 1 and 2. The [NO₂] doubles (1.51/0.756), while the [CO] remains constant. The rate increases by 4 fold (1.43/3.57). This tells us that the reaction is SECOND ORDER with respect to NO₂.

For CO, compare experiments 1 and 3. The [CO] doubles (0.532/0.266), while the [NO₂] remains constant. The rate does not change (0.357/0.357). This tells us the reaction in ZERO ORDER with respect to CO.

From this information, we can now write law for this reaction:

Rate = k[NO₂]²

To find k, we choose any experiment, and plug in the necessary data. We will use the data from experiment 1.

Rate = k[NO₂]²

0.357 M/s = k[0.756 M]²

0.357 M/s = 0.572 M² k

k = 0.357 M/s ÷ 0.572 M²

k = 0.624 M^-1s^-1