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- Suppose that a catalyst lowers the activation barrier of a reaction from 125 kJ/mol to 55 kJ/mol. By what factor would you expect the reaction rate to increase at 25 °C? (Assume that the frequency factors for the catalyzed and uncatalyzed reactions are identical.)
Problem 81
Problem 82
The activation barrier for the hydrolysis of sucrose into glucose and fructose is 108 kJ/mol. If an enzyme increases the rate of the hydrolysis reaction by a factor of 1 million, how much lower must the activation barrier be when sucrose is in the active site of the enzyme? (Assume that the frequency factors for the catalyzed and uncatalyzed reactions are identical and a temperature of 25 °C.)
- How long will it take for 90% of the CH3CN to convert to CH3NC at 500 °C given the tabulated data: Time (h) [CH3CN] (M) 0.0 1.000, 5.0 0.794, 10.0 0.631, 15.0 0.501, 20.0 0.398, 25.0 0.316?
Problem 83
Problem 83a
The tabulated data were collected for this reaction at 500 °C: CH3CN(g) → CH3NC( g) a. Determine the order of the reaction and the value of the rate constant at this temperature.
Problem 83b
The tabulated data were collected for this reaction at 500 °C: CH3CN(g) → CH3NC( g) b. What is the half-life for this reaction (at the initial concentration)?
- What is the half-life for this reaction at the initial concentration?
Problem 84
Problem 84a
The tabulated data were collected for this reaction at a certain temperature: X2Y → 2 X + Y a. Determine the order of the reaction and the value of the rate constant at this temperature.
Problem 84c
The tabulated data were collected for this reaction at a certain temperature: X2Y → 2 X + Y c. What is the concentration of X after 10.0 hours?
- Consider the reaction: A + B + C → D. The rate law for this reaction is: Rate = k [A][C]^2 [B]^1/2. Suppose the rate of the reaction at certain initial concentrations of A, B, and C is 0.0115 M/s. What is the rate of the reaction if the concentrations of A and C are doubled and the concentration of B is tripled?
Problem 85
Problem 86
Consider the reaction: 2 O3(g) → 3 O2( g) The rate law for this reaction is: Rate = k [O3]2 [O2] Suppose that a 1.0-L reaction vessel initially contains 1.0 mol of O3 and 1.0 mol of O2. What fraction of the O3 will have reacted when the rate falls to one-half of its initial value?
- At 700 K, acetaldehyde decomposes in the gas phase to methane and carbon monoxide. The reaction is: CH3CHO(g) → CH4(g) + CO(g). A sample of CH3CHO is heated to 700 K and the pressure is measured as 0.22 atm before any reaction takes place. The kinetics of the reaction are followed by measurements of total pressure and these data are obtained: t (s) 0 1000 3000 7000; PTotal (atm) 0.22 0.24 0.27 0.31. Find the rate law, the rate constant, and the total pressure after 2.00 × 10^4 s.
Problem 87
- At 400 K, oxalic acid decomposes according to the reaction: H2C2O4(g) → CO2(g) + HCOOH(g). In three separate experiments, the initial pressure of oxalic acid and the final total pressure after 20,000 seconds are measured. Experiment: 1) PH2C2O4 at t = 0: 65.8, PTotal at t = 20,000 s: 94.6; 2) PH2C2O4 at t = 0: 92.1, PTotal at t = 20,000 s: 132; 3) PH2C2O4 at t = 0: 111, PTotal at t = 20,000 s: 160. Find the rate law of the reaction and its rate constant.
Problem 88
Problem 89
Dinitrogen pentoxide decomposes in the gas phase to form nitrogen dioxide and oxygen gas. The reaction is first order in dinitrogen pentoxide and has a half-life of 2.81 h at 25 °C. If a 1.5-L reaction vessel initially contains 745 torr of N2O5 at 25 °C, what partial pressure of O2 is present in the vessel after 215 minutes?
Problem 91
Iodine atoms combine to form I2 in liquid hexane solvent with a rate constant of 1.5⨉1010 L/mols. The reaction is second order in I. Since the reaction occurs so quickly, the only way to study the reaction is to create iodine atoms almost instantaneously, usually by photochemical decomposition of I2. Suppose a flash of light creates an initial [I] concentration of 0.0100 M. How long will it take for 95% of the newly created iodine atoms to recombine to form I2?
- Is the question asking for the mass of sucrose hydrolyzed when 2.55 L of a 0.150 M sucrose solution is allowed to react for 195 minutes, given that the hydrolysis of sucrose (C12H22O11) into glucose and fructose in acidic water has a rate constant of 1.8 * 10^-4 s^-1 at 25 °C and the reaction is first order in sucrose?
Problem 92
- The reaction AB(aq) → A(g) + B(g) is second order in AB and has a rate constant of 0.0118 M^-1 s^-1 at 25.0 °C. A reaction vessel initially contains 250.0 mL of 0.100 M AB that is allowed to react to form the gaseous product. The product is collected over water at 25.0 °C. How much time is required to produce 200.0 mL of the products at a barometric pressure of 755.1 mmHg? (The vapor pressure of water at this temperature is 23.8 mmHg.)
Problem 93
- The reaction 2 H2O2(aq) → 2 H2O(l) + O2(g) is first order in H2O2 and under certain conditions has a rate constant of 0.00752 s⁻¹ at 20.0 °C. A reaction vessel initially contains 150.0 mL of 30.0% H2O2 by mass solution (the density of the solution is 1.11 g/mL). The gaseous oxygen is collected over water at 20.0 °C as it forms. What volume of O2 forms in 85.0 seconds at a barometric pressure of 742.5 mmHg? (The vapor pressure of water at this temperature is 17.5 mmHg.)
Problem 94
Problem 95a
Consider this energy diagram:
a. How many elementary steps are involved in this reaction?
Problem 95b
Consider this energy diagram:
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b. Label the reactants, products, and intermediates.
Problem 95c
Consider this energy diagram:
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c. Which step is rate limiting?
Problem 95d
Consider this energy diagram:
d. Is the overall reaction endothermic or exothermic?
- Is the overall reaction exothermic or endothermic in the mechanism where HCl adds across the double bond of ethene to form H3C¬CH2Cl, with the energy diagram indicating step 1 as HCl + H2C“CH2 → H3C“CH2+ + Cl⁻ and step 2 as H3C“CH2+ + Cl⁻ → H3C¬CH2Cl?
Problem 96
Problem 96a
Consider the reaction in which HCl adds across the double bond of ethene: HCl + H2C=CH2 → H3C-CH2Cl The following mechanism, with the accompanying energy diagram, has been suggested for this reaction:
Step 1 HCl + H2C=CH2 → H3C=CH2+ + Cl-
Step 2 H3C=CH2+ + Cl- → H3C-CH2Cl
a. Based on the energy diagram, determine which step is rate limiting.
Problem 96b
Consider the reaction in which HCl adds across the double bond of ethene: HCl + H2C=CH2 → H3C-CH2Cl The following mechanism, with the accompanying energy diagram, has been suggested for this reaction:
Step 1 HCl + H2C=CH2 → H3C=CH2+ + Cl-
Step 2 H3C=CH2+ + Cl- → H3C-CH2Cl
b. What is the expected order of the reaction based on the proposed mechanism?
- The desorption (leaving of the surface) of a single molecular layer of n-butane from a single crystal of aluminum oxide is found to be first order with a rate constant of 0.128 s−1 at 150 K. If the surface is initially completely covered, what fraction will remain covered after 10 s? After 20 s?
Problem 97
Problem 97a
The desorption (leaving of the surface) of a single molecular layer of n-butane from a single crystal of aluminum oxide is found to be first order with a rate constant of 0.128/s at 150 K. a. What is the half-life of the desorption reaction?-
Problem 97b
The desorption (leaving of the surface) of a single molecular layer of n-butane from a single crystal of aluminum oxide is found to be first order with a rate constant of 0.128/s at 150 K. b. If the surface is initially completely covered with n-butane at 150 K, how long will it take for 25% of the molecules to desorb (leave the surface)? For 50% to desorb?
- What fraction of the film is left after 10 s, assuming the same initial coverage as in part a, given that the evaporation of a 120-nm film of n-pentane from a single crystal of aluminum oxide is zero order with a rate constant of 1.92 * 10^13 molecules/cm^2 * s at 120 K?
Problem 98
Problem 98a
The evaporation of a 120-nm film of n-pentane from a single crystal of aluminum oxide is zero order with a rate constant of 1.92⨉1013 molecules/cm2•s at 120 K. a. If the initial surface coverage is 8.9⨉1016 molecules/cm2, how long will it take for one-half of the film to evaporate?
Problem 99a
The kinetics of this reaction were studied as a function of temperature. (The reaction is first order in each reactant and second order overall.)
C2H5Br(aq) + OH- (aq) → C2H5OH(l) + Br- (aq)
Temperature (°C) k (L,mol •s)
25 8.81⨉10-5
35 0.000285
45 0.000854
55 0.00239
65 0.00633
a. Determine the activation energy and frequency factor for the reaction.