Name: ________________________________ Problem Set 37b- AP Kinetics Problems 1980 The decomposition of compound X is an elementary process that proceeds as follows:

X(g) ←→kr

kfA(g) + B(g) ΔH˚= +15 kilocalories

The forward reaction is slow at room temperature but becomes rapid when a catalyst is added. (a) Draw a diagram of potential energy vs reaction coordinate for the uncatalyzed reaction. On this diagram label:

(1) the axes (2) the energies of the reactants and the products (3) the energy of the activated complex (4) activation energy and ΔHreaction for both forward and reverse reactions.

(b) On the same diagram indicate the change or changes that result from the addition of the catalyst. Explain the role of the catalyst in changing the rate of the reaction.

2004-B

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2H2O2(aq) → 2H2O(l) + O2(g)

Hydrogen peroxide decomposes according to the above reaction. a) An aqueous solution of hydrogen peroxide that is 6.00 percent H2O2 by mass has a density of 1.03 g ml-. Calculate each

of the following. i. The original number of moles of H2O2 in a 125 ml sample of the 6.00 % H2O2 solution. (0.227 moles)

ii. The number of moles of O2 that are produced when all of the H2O2 in the 125 ml sample decomposes. (0.114 mole O2)

b) The graphs below show the results from a study of the decomposition of H2O2.

i. Write the rate law for the reaction. Justify your answer.

ii. Determine the half life of the reaction.

iii. Calculate the value of the rate constant, k. Include appropriate units in your answer. (1.1 x 10-3 min-1)

iv. Determine the [H2O2] after 2000 minutes elapse from the time the reaction began. (0.11 M)

2004 -A The decomposition of chemical species, X, into product Y is a first order reaction. The data from an experiment are given in the table below.

a) Calculate the rate constant for the first order reaction using the values given for concentration and time. Include units with your answer. (3.14 x 10-2 min-1)

b) Calculate the number of minutes that it takes for the concentration of X to drop to 1.50 x 10-5 M. (66.2 min)

c) Calculate the half life for the reaction. Include units with your answer. (22.1 min)

d) Experiments were performed to determine the rate constant for this reaction at various temperatures. Data from these experiments were used to produce the graph below, where T is temperature. This graph can be used to determine the activation energy, Ea, of the reaction.

i. Label the vertical axis of the graph ii. Explain how to calculate the activation energy from this graph.

2003 B The decay of the radioisotope I-131 was studied in the laboratory. The radioactivity of the sample of I-131 was measured and is plotted on the graph below.

a) Determine the half-life, t1/2, of I-131 using the graph to the right.

b) The data can be used to show that the decay of I-131 is a first order reaction, as indicated on the graph below. i. Label the vertical axis of the graph.

ii. What are the units of the rate constant, k, for the

decay reaction?

iii. Explain how the half life of I-131 can be calculated using the slope of the line plotted on the graph.

c) Compare the value if the half life of I-131 at 25°C to its value at 50°C.

[X] Time (min) 1.20 x 10-4 0.00 4.00 x 10-5 35.00 3.00 x 10-5 44.20 1.50 x 10-5 ?