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Problem 55b
The gas-phase reaction Cl(g) + HBr(g) → HCl(g) + Br(g) has an overall energy change of -66 kJ. The activation energy for the reaction is 7 kJ. (b) What is the activation energy for the reverse reaction?
- For the elementary process N2O5(g) → 2NO2(g) + NO3(g), the activation energy (Ea) and overall ΔE are 154 kJ/mol and 136 kJ/mol, respectively. (a) Sketch the energy profile for this reaction, and label Ea and ΔE.
Problem 56
- Indicate whether each statement is true or false. (a) If you compare two reactions with similar collision factors, the one with the larger activation energy will be slower. (b) A reaction that has a small rate constant must have a small frequency factor.
Problem 57
Problem 57c
Indicate whether each statement is true or false. (c) Increasing the reaction temperature increases the fraction of successful collisions between reactants.
Problem 58a
Indicate whether each statement is true or false. (a) If you measure the rate constant for a reaction at different temperatures, you can calculate the overall enthalpy change for the reaction.
Problem 58b
Indicate whether each statement is true or false. (b) Exothermic reactions are faster than endothermic reactions.
Problem 58c
Indicate whether each statement is true or false. (c) If you double the temperature for a reaction, you cut the activation energy in half.
Problem 59
Based on their activation energies and energy changes and assuming that all collision factors are the same, rank the following reactions from slowest to fastest. (a) Ea = 45 kJ>mol; E = -25 kJ>mol (b) Ea = 35 kJ>mol; E = -10 kJ>mol (c) Ea = 55 kJ>mol; E = 10 kJ>mol
- (a) A certain first-order reaction has a rate constant of 2.75 * 10^-2 s^-1 at 20 _x001E_C. What is the value of k at 60 _x001E_C if Ea = 75.5 kJ/mol? (b) Another first-order reaction also has a rate constant of 2.75 * 10^-2 s^-1 at 20 _x001E_C. What is the value of k at 60 _x001E_C if Ea = 125 kJ/mol?
Problem 61
- Understanding the high-temperature behavior of nitrogen oxides is essential for controlling pollution generated in automobile engines. The decomposition of nitric oxide (NO) to N2 and O2 is second order with a rate constant of 0.0796 M-1s-1 at 737 _x001E_C and 0.0815 M-1s-1 at 947 _x001E_C. Calculate the activation energy for the reaction.
Problem 62
- 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.
- What is meant by the term elementary reaction? What is a reaction mechanism? What is meant by the term rate-determining step?
Problem 65
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?
- The following mechanism has been proposed for the gas-phase reaction of H2 with ICl: H2(g) + ICl(g) → HI(g) + HCl(g), HI(g) + ICl(g) → I2(g) + HCl(g). (c) If the first step is slow and the second one is fast, which rate law do you expect to be observed for the overall reaction?
Problem 71
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