First Year Chemistry

Worksheet for Rates of Reaction Unit

For problems 1-5 find the rate law for the reaction using the concentration/rate data. Determine the value of the rate constant along with the units.

1.         H2O2 + 2HI à 2H2O + I2

Trial                 [H2O2]              [HI]                  rate (mol/L/sec)
1                       0.10 M              0.10 M              0.0076
2                       0.10 M              0.20 M              0.0152
3                       0.20 M              0.10 M              0.0152

2.         H2 + I2 à 2HI

Trial                 [H2]                  [I2]                    rate (mol/L/sec)
1                       1.0 mol/L         1.0 mol/L         0.20
2                       1.0                    2.0                    0.40
3                       2.0                    2.0                    0.80

3.         2NO2 + F2 à 2NO2F

Trial                 [NO2]               [F2]                   rate (mol/L/min)
1                       1.0 mol/L         1.0 mol/L         1.0 x 10-4
2                       2.0                    1.0                    2.0 x 10-4
3                       1.0                    2.0                    2.0 x 10-4

4.         2NO + Br2 à 2NOBr

Trial                 [NO]                 [Br2]                 rate (mol/L/hr)
1                       1.0 mol/L         1.0 mol/L         1.30 x 10-3
2                       2.0                    1.0                    5.20 x 10-3
3                       4.0                    2.0                    4.16 x 10-2

5.         ClO3- + 9I- + 6H+ à 3I3- + Cl- + 2H2O

Trial                 [ClO3-]              [I-]                    [H+]                  rate
1                       0.10 M              0.10 M              0.10 M              X
2                       0.10                 0.20                  0.10                  2X
3                       0.20                  0.20                  0.10                  4X
4                       0.20                  0.20                  0.20                  16X

Given the rate law provided, predict the effect on the initial rate of the following changes in the conditions (temperature, concentration, volume)

6.         Nitrogen monoxide gas and hydrogen gas react according to the rate law
            Rate = k[NO]2[H2]. How does the rate change if:

    1. the concentration of hydrogen is doubled.
    2. the concentration of nitrogen monoxide is doubled.
    3. the concentration of hydrogen is cut in half.
    4. the volume of the container is cut in half.
    5. the volume of the container is doubled.
    6. the temperature is increased.
    7. the concentration of nitrogen monoxide is doubled while the concentration of hydrogen is cut in half.
    8. the concentration of hydrogen is doubled while the concentration of nitrogen monoxide is cut in half.

7.    The rate law of a particular reaction between gases X, Y and Z is found to be
        Rate = k[X]0[Y]2[Z]. How does the initial rate change if:

    1. the concentration of X is doubled.
    2. the concentration of Y is tripled.
    3. the concentration of Z is quadrupled.
    4. the volume of the container is cut in half.
    5. the volume of the container is doubled.
    6. the temperature is increased.
    7. the concentration of X is quadrupled while the concentration of Y and Z are doubled.
    8. the concentration of Z is cut in half while the concentration of Y is doubled.
    9. the concentration of Y and Z are tripled while the concentration of X is cut in thirds.

Mechanisms:

8.         Determine the rate laws for the following single-step reactions:

    1. 2NO2 à NO + NO3
    2. NO3 + CO à CO2 + NO2
    3. xA + yB à zC

9.         For the reactions below, the mechanism is shown. From the mechanism, determine the
            rate law.

            For the reaction: 2NO2Cl à 2NO2 + Cl2   the following mechanism has been proposed:

STEP 1:            NO2Cl à NO2 + Cl                      slow
STEP 2:            NO2Cl + Cl à NO2 + Cl2           fast

Which step is the rate determining step? Explain your reasoning.

From your choice, write the rate law for the reaction.

10.       The reaction    2NO + O2 à 2NO2      exhibits the rate law Rate = k[NO]2[O2].   Which
            of the following mechanisms is consistent with this rate law? Explain your reasoning.

1)          NO + O2 à NO2 + O   (slow)
         O + NO à NO2                        (fast)

2)          NO + O2 à NO3                      (fast)
            NO + NO3 à 2NO2      (slow)

3)          2NO à 2N2O2             (slow)
            N2O2 + O2 à N2O4                   (fast)
            N2O4 à 2NO2              (fast)

CHECK YOUR ANSWERS

Return to Unit