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- The rate of the reaction CH3COOC2H5(aq) + OH-(aq) → CH3COO-(aq) + C2H5OH(aq) was measured at several temperatures, and the following data were collected: Temperature (°C) k (M⁻¹ s⁻¹) 15 0.0521 25 0.101 35 0.184 45 0.332. Calculate the value of Ea by constructing an appropriate graph.
Problem 63
Problem 64
The temperature dependence of the rate constant for a reaction is tabulated as follows: Temperature (K) k 1M 1 s1 2 600 0.028 650 0.22 700 1.3 750 6.0 800 23 Calculate Ea and A.
Problem 65b
(b) What is the difference between a unimolecular and a bimolecular elementary reaction?
- (a) Can an intermediate appear as a reactant in the first step of a reaction mechanism? (b) On a reaction energy profile diagram, is an intermediate represented as a peak or a valley?
Problem 66
Problem 67a
What is the molecularity of each of the following elementary reactions? Write the rate law for each. (a) Cl2(g) → 2 Cl(g)
Problem 67b
What is the molecularity of each of the following elementary reactions? Write the rate law for each. (b) OCl-(aq + H2O(l) → HOCl(aq) + OH-(aq)
Problem 67c
What is the molecularity of each of the following elementary reactions? Write the rate law for each. (c) NO(g) + Cl2(g) → NOCl2(g)
Problem 68a,b
What is the molecularity of each of the following elementary reactions? Write the rate law for each.
(a) 2 NO(g) → N2O2(g)
(c) SO3(g) → SO2(g) + O(g)
Problem 68b
What is the molecularity of each of the following elementary reactions? Write the rate law for each. (b)
Problem 69a
(a) Based on the following reaction profile, how many intermediates are formed in the reaction A→D?
Problem 69c
(c) Which step is the fastest?
Problem 70a
Consider the following energy profile.
(a) How many elementary reactions are in the reaction mechanism?
Problem 70b
Consider the following energy profile.
(b) How many intermediates are formed in the reaction?
Problem 70c
Consider the following energy profile.
(c) Which step is rate limiting?
Problem 72a
The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism:
H2O2(aq) + I-(aq) → H2O(l) + IO-(aq) (slow)
IO-(aq) + H2O2(aq) → H2O(l) + O2(g) + I-(aq) (fast)
(a) Write the chemical equation for the overall process.
Problem 72b
The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism:
H2O2(aq) + I-(aq) → H2O(l) + IO-(aq) (slow)
IO-(aq) + H2O2(aq) → H2O(l) + O2(g) + I-(aq) (fast)
(b) Identify the intermediate, if any, in the mechanism.
Problem 72c
The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism:
H2O2(aq) + I-(aq) → H2O(l) + IO-(aq) (slow)
IO-(aq) + H2O2(aq) → H2O(l) + O2(g) + I-(aq) (fast)
(c) Assuming that the first step of the mechanism is rate determining, predict the rate law for the overall process.
Problem 73a
The reaction 2 NO1g2 + Cl21g2¡2 NOCl1g2 was performed and the following data were obtained under conditions of constant 3Cl24:
![Graph showing the linear relationship of ln[H2] over time in chemical kinetics.](https://lightcat-files.s3.amazonaws.com/problem_images/b13cc8f7b3c6acff-1666285465032.jpg)
(a) Is the following mechanism consistent with the data? NO1g2 + Cl21g2ΔNOCl21g2 1fast2 NOCl21g2 + NO1g2¡2 NOCl1g2 1slow2
Problem 74a
You have studied the gas-phase oxidation of HBr by O2: 4 HBr(g) + O2(g) → 2 H2O(g) + 2 Br2(g)
You find the reaction to be first order with respect to HBr and first order with respect to O2. You propose the following mechanism:
HBr(g) + O2(g) → HOOBr(g)
HOOBr(g) + HBr(g) → 2 HOBr(g)
HOBr(g) + HBr(g) → H2O(g) + Br2(g)
(a) Confirm that the elementary reactions add to give the overall reaction.
Problem 74b
You have studied the gas-phase oxidation of HBr by O2: 4 HBr(g) + O2(g) → 2 H2O(g) + 2 Br2(g)
You find the reaction to be first order with respect to HBr and first order with respect to O2. You propose the following mechanism:
HBr(g) + O2(g) → HOOBr(g)
HOOBr(g) + HBr(g) → 2 HOBr(g)
HOBr(g) + HBr(g) → H2O(g) + Br2(g)
(b) Based on the experimentally determined rate law, which step is rate determining?
Problem 75a,b
(a) What is a catalyst? (b) What is the difference between a homogeneous and a heterogeneous catalyst?
Problem 75c
(c) Do catalysts affect the overall enthalpy change for a reaction, the activation energy, or both?
Problem 76a
(a) Most commercial heterogeneous catalysts are extremely finely divided solid materials. Why is particle size important?
- In solution, chemical species as simple as H+ and OH- can serve as catalysts for reactions. Imagine you could measure the [H+] of a solution containing an acid-catalyzed reaction as it occurs. Assume the reactants and products themselves are neither acids nor bases. Sketch the [H+] concentration profile you would measure as a function of time for the reaction, assuming t = 0 is when you add a drop of acid to the reaction.
Problem 78
- The oxidation of SO2 to SO3 is accelerated by NO2. The reaction proceeds according to: NO2(g) + SO2(g) → NO(g) + SO3(g) 2 NO(g) + O2(g) → 2 NO2(g) (a) Show that, with appropriate coefficients, the two reactions can be summed to give the overall oxidation of SO2 by O2 to give SO3. (d) Is this an example of homogeneous catalysis or heterogeneous catalysis?
Problem 79
Problem 80b
The addition of NO accelerates the decomposition of N2O, possibly by the following mechanism: NO1g2 + N2O1g2¡N21g2 + NO21g2 2 NO21g2¡2 NO1g2 + O21g2 (b) Is NO serving as a catalyst or an intermediate in this reaction?
Problem 80c
The addition of NO accelerates the decomposition of N2O, possibly by the following mechanism:
NO(g) + N2O(g) → N2(g) + NO2(g)
2 NO2(g) → 2 NO(g) + O2(g)
(c) If experiments show that during the decomposition of N2O, NO2 does not accumulate in measurable quantities, does this rule out the proposed mechanism?
Problem 81b
Many metallic catalysts, particularly the precious-metal ones, are often deposited as very thin films on a substance of high surface area per unit mass, such as alumina (Al2O3) or silica (SiO2). (b) How does the surface area affect the rate of reaction?
- The enzyme carbonic anhydrase catalyzes the reaction CO2(g) + H2O(l) ↔ HCO3⁻(aq) + H⁺(aq). In water, without the enzyme, the reaction proceeds with a rate constant of 0.039 s⁻¹ at 25 _x001E_C. In the presence of the enzyme in water, the reaction proceeds with a rate constant of 1.0 * 10⁶ s⁻¹ at 25 _x001E_C. Assuming the collision factor is the same for both situations, calculate the difference in activation energies for the uncatalyzed versus enzyme-catalyzed reaction.
Problem 85
Problem 86b
The enzyme urease catalyzes the reaction of urea, (NH2CONH2), with water to produce carbon dioxide and ammonia. In water, without the enzyme, the reaction proceeds with a first-order rate constant of 4.15 × 10-5 s-1 at 100°C. In the presence of the enzyme in water, the reaction proceeds with a rate constant of 3.4 × 104 s-1 at 21°C. (b) If the rate of the catalyzed reaction were the same at 100°C as it is at 21°C, what would be the difference in the activation energy between the catalyzed and uncatalyzed reactions?