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- If a temperature increase from 10.0 °C to 20.0 °C doubles the rate constant for a reaction, what is the value of the activation energy for the reaction?
Problem 77
- If a temperature increase from 20.0 °C to 35.0 °C triples the rate constant for a reaction, what is the value of the activation energy for the reaction?
Problem 78
Problem 79
Consider these two gas-phase reactions: a. AA(g) + BB(g) → 2 AB(g) b. AB(g) + CD(g) → AC(g) + BD(g) If the reactions have identical activation barriers and are carried out under the same conditions, which one would you expect to have the faster rate?
Problem 80
Which of these two reactions would you expect to have the smaller orientation factor? Explain. a. O(g) + N2(g) → NO( g) + N(g) b. NO(g) + Cl2(g) → NOCl( g) + Cl(g)
Problem 81
Consider this overall reaction, which is experimentally observed to be second order in AB and zero order in C: AB + C → A + BC Is the following mechanism valid for this reaction? AB + AB →k1 AB2 + A Slow AB2 + C → k2 AB + BC Fast
- Consider this overall reaction, which is experimentally observed to be second order in X and first order in Y: X + Y → XY. a. Does the reaction occur in a single step in which X and Y collide? b. Is this two-step mechanism valid? 2X →k1/k2 X2 (Fast) X2 + Y →k3 XY + X (Slow)
Problem 82
Problem 83a
Consider this three-step mechanism for a reaction:
Cl2 (g) k1⇌k2 2 Cl (g) Fast
Cl (g) + CHCl3 (g) →k3 HCl (g) + CCl3 (g) Slow
Cl (g) + CCl3 (g) →k4 CCl4 (g) Fast
a. What is the overall reaction?
Problem 83c
Consider this three-step mechanism for a reaction:
Cl2 (g) k1⇌k2 2 Cl (g) Fast
Cl (g) + CHCl3 (g) →k3 HCl (g) + CCl3 (g) Slow
Cl (g) + CCl3 (g) →k4 CCl4 (g) Fast
c. What is the predicted rate law?
- Consider this two-step mechanism for a reaction: Step 1: NO2(g) + Cl2(g) → ClNO2(g) + Cl(g) Slow Step 2: NO2(g) + Cl(g) → ClNO2(g) Fast c. What is the predicted rate law? a. What is the overall reaction?
Problem 84
Problem 84b
Consider this two-step mechanism for a reaction: NO2(g) + Cl2(g) → k1 ClNO2(g) + Cl g) Slow NO2(g) + Cl(g) →k2 ClNO2(g) Fast b. Identify the intermediates in the mechanism.
Problem 85
Many heterogeneous catalysts are deposited on high-surfacearea supports. Why?
Problem 86
Suppose that the reaction A¡products is exothermic and has an activation barrier of 75 kJ/mol. Sketch an energy diagram showing the energy of the reaction as a function of the progress of the reaction. Draw a second energy curve showing the effect of a catalyst.
- 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 87
Problem 88
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 89
Problem 89a
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 89b
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)?
Problem 90a
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 90c
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 91
Problem 92
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 93
- 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 94
Problem 95
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 97
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 98
- 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 99
Problem 101a
Consider this energy diagram:
a. How many elementary steps are involved in this reaction?
Problem 101d
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 102