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- The following data were collected for the rate of disappearance of NO in the reaction 2 NO(g) + O2(g) → 2 NO2(g): Experiment [NO] (M) [O2] (M) Initial Rate (M/s) 1 0.0126 0.0125 1.41 * 10^-2 2 0.0252 0.0125 5.64 * 10^-2 3 0.0252 0.0250 1.13 * 10^-1 (d) What is the rate of disappearance of NO when [NO] = 0.0750 M and [O2] = 0.0100 M? (e) What is the rate of disappearance of O2 at the concentrations given in part (d)?
Problem 36
- Consider the gas-phase reaction between nitric oxide and bromine at 273 _x001E_C: 2 NO(g) + Br2(g) → 2 NOBr(g). The following data for the initial rate of appearance of NOBr were obtained: Experiment [NO] (M) [Br2] (M) Initial Rate (M/s) 1 0.10 0.20 24 2 0.25 0.20 150 3 0.10 0.50 60 4 0.35 0.50 735 (c) How is the rate of appearance of NOBr related to the rate of disappearance of Br2? (d) What is the rate of disappearance of Br2 when [NO] = 0.075 M and [Br2] = 0.25 M?
Problem 37
Problem 37b
Consider the gas-phase reaction between nitric oxide and bromine at 273°C: 2 NO(g) + Br2(g) → 2 NOBr(g). The following data for the initial rate of appearance of NOBr were obtained:
Experiment [NO] (M) [Br2] (M) Initial Rate (M/s)
1 0.10 0.20 24
2 0.25 0.20 150
3 0.10 0.50 60
4 0.35 0.50 735
(b) Calculate the average value of the rate constant for the appearance of NOBr from the four data sets.
- Consider the reaction of peroxydisulfate ion S2O8^2- with iodide ion I^- in aqueous solution: S2O8^2- (aq) + 3 I^- (aq) → 2 SO4^2- (aq) + I3^- (aq). At a particular temperature, the initial rate of disappearance of S2O8^2- varies with reactant concentrations in the following manner: Experiment S2O8^2- [M] I^- [M] Initial Rate [M/s] 1 0.018 0.036 2.6 * 10^-6 2 0.027 0.036 3.9 * 10^-6 3 0.036 0.054 7.8 * 10^-6 4 0.050 0.072 1.4 * 10^-5 (b) What is the average value of the rate constant for the disappearance of S2O8^2- based on the four sets of data? (c) How is the rate of disappearance of S2O8^2- related to the rate of disappearance of I^-? (d) What is the rate of disappearance of I^- when [S2O8^2-] = 0.025 M and [I^-] = 0.050 M?
Problem 38
Problem 38a
Consider the reaction of peroxydisulfate ion (S2O82-) with iodide ion (I-) in aqueous solution:
S2O82-(aq) + 3 I-(aq) → 2 SO42-(aq) + I3-(aq)
At a particular temperature, the initial rate of disappearance of S2O82- varies with reactant concentrations in the following manner:
Experiment [S2O82-] (M) [I-] (M) Initial Rate (M/s)
1 0.018 0.036 2.6 × 10-6
2 0.027 0.036 3.9 × 10-6
3 0.036 0.054 7.8 × 10-6
4 0.050 0.072 1.4 × 10-5
(a) Determine the rate law for the reaction and state the units of the rate constant.
Problem 39a
(a) For the generic reaction A → B what quantity, when graphed versus time, will yield a straight line for a first-order reaction?
Problem 39b
(b) How can you calculate the rate constant for a first-order reaction from the graph you made in part (a)?
Problem 40b
The decomposition of sodium bicarbonate (baking soda), NaHCO3(s), into Na2CO3(s), H2O(l), and CO2(g) at constant pressure requires the addition of 85 kJ of heat per two moles of NaHCO3. (b) Draw an enthalpy diagram for the reaction.
Problem 41a
(a) The gas-phase decomposition of SO2Cl2, SO2Cl2(g) → SO2(g) + Cl2(g), is first order in SO2Cl2. At 600 K the half-life for this process is 2.3 × 105 s. What is the rate constant at this temperature?
Problem 41b
(b) At 320°C the rate constant is 2.2 × 10-5 s-1. What is the half-life at this temperature?
- Molecular iodine, I2(g), dissociates into iodine atoms at 625 K with a first-order rate constant of 0.271 s-1. (b) If you start with 0.050 M I2 at this temperature, how much will remain after 5.12 s assuming that the iodine atoms do not recombine to form I2?
Problem 42
Problem 43a
As described in Exercise 14.41, the decomposition of sulfuryl chloride (SO2Cl2) is a first-order process. The rate constant for the decomposition at 660 K is 4.5 × 10-2 s-1. (a) If we begin with an initial SO2Cl2 pressure of 450 torr, what is the partial pressure of this substance after 60 s?
Problem 43b
As described in Exercise 14.41, the decomposition of sulfuryl chloride (SO2Cl2) is a first-order process. The rate constant for the decomposition at 660 K is 4.5 × 10-2 s-1. (b) At what time will the partial pressure of SO2Cl2 decline to one-tenth its initial value?
- The first-order rate constant for the decomposition of N2O5, 2 N2O5(g) → 4 NO2(g) + O2(g), at 70 °C is 6.82 * 10-3 s-1. Suppose we start with 0.0250 mol of N2O5(g) in a volume of 2.0 L. (b) How many minutes will it take for the quantity of N2O5 to drop to 0.010 mol?
Problem 44
Problem 44a
The first-order rate constant for the decomposition of N2O5, 2 N2O5(g) → 4 NO2(g) + O2(g), at 70°C is 6.82×10-3 s-1. Suppose we start with 0.0250 mol of N2O5(g) in a volume of 2.0 L. (a) How many moles of N2O5 will remain after 5.0 min?
Problem 44c
The first-order rate constant for the decomposition of N2O5, 2 N2O5(g) → 4 NO2(g) + O2(g), at 70°C is 6.82×10-3 s-1. Suppose we start with 0.0250 mol of N2O5(g) in a volume of 2.0 L. (c) What is the half-life of N2O5 at 70°C?
- The reaction SO2Cl2(g) → SO2(g) + Cl2(g) is first order in SO2Cl2. Using the following kinetic data, determine the magnitude and units of the first-order rate constant: Time (s) Pressure SO2Cl2 (atm) 0 1.000 2500 0.947 5000 0.895 7500 0.848 10,000 0.803
Problem 45
Problem 46
From the following data for the first-order gas-phase isomerization of CH3NC at 215 C, calculate the firstorder rate constant and half-life for the reaction: Time (s) Pressure CH3nC (torr) 0 502 2000 335 5000 180 8000 95.5 12,000 41.7 15,000 22.4
Problem 47a
Consider the data presented in Exercise 14.19. (a) By using appropriate graphs, determine whether the reaction is first order or second order.
Problem 47c
Consider the data presented in Exercise 14.19. (c) What is the half-life for the reaction?
- Consider the data presented in Exercise 14.20. (a) Determine whether the reaction is first order or second order.
Problem 48
Problem 49a,c
The gas-phase decomposition of NO2, 2 NO2(g) → 2 NO(g) + O2(g), is studied at 383°C, giving the following data:
Time (s) [NO2] (M)
0.0 0.100
5.0 0.017
10.0 0.0090
15.0 0.0062
20.0 0.0047
(a) Is the reaction first order or second order with respect to the concentration of NO2?
(c) Predict the reaction rates at the beginning of the reaction for initial concentrations of 0.200 M, 0.100 M, and 0.050 M NO2.
Problem 50a
Sucrose 1C12H22O112, commonly known as table sugar, reacts in dilute acid solutions to form two simpler sugars, glucose and fructose, both of which have the formula C6H12O6. At 23 C and in 0.5 M HCl, the following data were obtained for the disappearance of sucrose: Time (min) 3C12H22o11 4 1M2 0 0.316 39 0.274 80 0.238 140 0.190 210 0.146 (a) Is the reaction first order or second order with respect to 3C12H22O114?
- (c) Which factor is most sensitive to changes in temperature—the frequency of collisions, the orientation factor, or the fraction of molecules with energy greater than the activation energy?
Problem 51
Problem 51a
(a) What factors determine whether a collision between two molecules will lead to a chemical reaction?
Problem 51b
(b) Does the rate constant for a reaction generally increase or decrease with an increase in reaction temperature?
- (a) In which of the following reactions would you expect the orientation factor to be least important in leading to the reaction: NO + O → NO2 or H + Cl → HCl? (b) Does the orientation factor depend on temperature?
Problem 52
Problem 53
Calculate the fraction of atoms in a sample of argon gas at 400 K that has an energy of 10.0 kJ or greater.
Problem 54
(a) The activation energy for the isomerization of methyl isonitrile (Figure 14.6) is 160 kJ>mol. Calculate the fraction of methyl isonitrile molecules that has an energy equal to or greater than the activation energy at 500 K. (b) Calculate this fraction for a temperature of 520 K. What is the ratio of the fraction at 520 K to that at 500 K?
Problem 55a
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. (a) Sketch the energy profile for the reaction, and label Ea and ΔE.