Ch 11.4-11.5
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Grant DeRocher
Chem 167
Houk
04/7/13
1. The decomposition of N2O5 in solution in carbon tetrachloride is a first-order reaction.
2N2O5
4NO2 + O2 .
The rate constant at a given temperature is found to
be 5.25 x 10-4 s-1. If the initial concentration of N2O5 is 0.200 M, what is its concentration
after exactly 10 minutes have passed?
2. As with any drug, aspirin (acetylsalicylic acid) must remain in the bloodstream long
enough to be effective. Assume that the removal of aspirin from the bloodstream into the
urine is a first order reaction with a half-life of about 3 hours. The instructions on the
aspirin bottle say to take 1 or two tablets every 4 hours. If a person takes 2 aspirin tablets,
how much aspirin remains in the bloodstream when it is time for the second does? (A
standard tablet contains 325 mg of aspirin.
3. If the initial concentration of the reactant in a first-order reaction A
products is 0.64
mol/L and the half-life is 30.0 s,
(a) Calculate the concentration of the reactant exactly 60 s after initiation of the reaction.
(b) How long would it take for the concentration of the reactant to drop to one-eighth its
initial value?
(c) How long would it take for the concentration of the reactant to drop to 0.040 mol/L?
4. The activation energy for the reaction in which CO2 decomposes to CO and a free radical
oxygen atom, O, has an activation energy of 460 kJ/mol. The frequency factor is
2x1011 s-1. What is the rate constant for this reaction at 298 K?
5. The following rate constants were obtained in an experiment in which the decomposition
of gaseous N2O5 was studied as a function of temperature. The products were NO2 and
NO3.
k(s-1)
Temperature (K)
298
3.4 x 10-5
308
2.2 x 10-4
318
6.8 x 10-4
328
3.1 x 10-3
Determine Ea for this reaction in kJ/mol.
6. The table below presents rate constants measured at three temperatures for the following
reaction, which is involved in the production of nitrogen oxides in internal combustion
engines.
O(g) + N2(g)
NO(g) + N(g)
k(L/(mol*s))
4.4 x 102
2.5 x 105
5.9 x 106
Temperature (K)
2000
3000
4000
Determine the activation energy of the reaction in kJ/mol.