A reaction was shown to follow second-order kinetics. How much time is required for [A] to change from 0.500 M to 0.315 M? (k = 0.456 M⁻¹ s⁻¹)

A study of the rate of dimerization of C4H6 gave the data shown in the table: 2C4H6C8H12 (a) Determine the average rate of dimerization between 0 s and 1600 s, and between 1600 s and 3200 s. (b) Estimate the instantaneous rate of dimerization at 3200 s from a graph of time versus [C4H6]. What are the units of this rate? (c) Determine the average rate of formation of C8H12 at 1600 s and the instantaneous rate of formation at 3200 s from the rates found in parts (a) and (b).

At 620. K butadiene dimerizes at a moderate rate. The following data were obtained in an experiment involving this reaction: t(s) [C4H6] (mol/L) 0 0.01000 1000.. 0.00629 2000. 0.00459 3000. 0.00361 a. Determine the order of the reaction in butadiene. b. In how many seconds is the dimerization 1.0% complete? c. In how many seconds is the dimerization 10.0% complete? d. What is the half-life for the reaction if the initial concentration of butadiene is 0.0200 M? e. Use the results from this problem and Exercise 45 to calculate the activation energy for the dimerization of butadiene.

At 573 K, gaseous NO2(g) decomposes, forming NO(g) and O2(g). If a vessel containing NO2(g) has an initial concentration of 1.9 102 mol/L, how long will it take for 75% of the NO2(g) to decompose? The decomposition of NO2(g) is second-order in the reactant and the rate constant for this reaction, at 573 K, is 1.1 L/mol s.

Why does a catalyst increase the rate of a reaction? What is the difference between a homogeneous catalyst and a heterogeneous catalyst? Would a given reaction necessarily have the same rate law for both a catalyzed and an uncatalyzed pathway? Explain.

11.44 A possible reaction for the degradation of the pesticide DDT to a less harmful compound was simulated in the laboratory. The reaction was found to be first order, with k = 4.0 X 10_H s"' at 25°C. What is the half-life for the degradation of DDT in this experiment, in years?

Consider a hypothetical reaction between A and B: A + B products Use the following initial rate data to calculate the rate constant for this reaction. [A] (mol/L) [B] (mol/L) Initial Rate (mol/L s) 0.20 1.0 3.0 0.50 1.0 11.8 2.0 2.0 189.5

For a first order gas phase reaction A products, k = 7.2 104s1 at 660. K and k = 1.7 102s1 at 720. K. If the initial pressure of A is 536 torr at 295C, how long will it take for the pressure of A to decrease to 268 torr?

The initial concentration of the reactant in a tirst-order reaction A —» products is 0.64 rnol/L and the half-life is 30.0 s. Calculate the concentration of the reactant exactly 60 s after initiation of the reaction. How long would it take for the concentration of the reactant to drop to one-eighth its initial value? How long would it take for the concentration of the reactant to drop to 0.040 mol/L?

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 lirst-order reaction, with a half-life of about 3 hours. The instructions on an aspirin bottle say to take 1 or 2 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 dose? (A standard tablet contains 325 mg of aspirin.)