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- 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 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
- 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 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
Problem 102b
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?
Problem 103b
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 104
Problem 104a
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 105b
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
b. Determine the rate constant at 15 °C.
Problem 107a
This reaction has an activation energy of zero in the gas phase: CH3 + CH3 → C2H6
a. Would you expect the rate of this reaction to change very much with temperature?
Problem 108a
Consider the two reactions:
O + N2 → NO + N Ea = 315 kJ/mol
Cl + H2 → HCl + H Ea = 23 kJ/mol
a. Why is the activation barrier for the first reaction so much higher than that for the second?
Problem 108b
Consider the two reactions:
O + N2 → NO + N Ea = 315 kJ/mol
Cl + H2 → HCl + H Ea = 23 kJ/mol
b. The frequency factors for these two reactions are very close to each other in value. Assuming that they are the same, calculate the ratio of the reaction rate constants for these two reactions at 25 °C.
Problem 109
Anthropologists can estimate the age of a bone or other sample of organic matter by its carbon-14 content. The carbon-14 in a living organism is constant until the organism dies, after which carbon- 14 decays with first-order kinetics and a half-life of 5730 years. Suppose a bone from an ancient human contains 19.5% of the C-14 found in living organisms. How old is the bone?
Problem 111b
Consider the gas-phase reaction: H2(g) + I2(g) → 2 HI(g) The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms. Proposed mechanism I: H2(g) + I2(g) → 2 HI(g) Single step Proposed mechanism II: I2(g) Δk1k-12 I(g) Fast H2( g) + 2 I( g) → k22 HI( g) Slow b. What kind of experimental evidence might lead you to favor mechanism II over mechanism I?
- What rate law corresponds to the proposed mechanism for the formation of hydrogen bromide, which can be written in a simplified form as: Br2(g) → 2Br(g) (Fast) Br(g) + H2(g) → HBr(g) + H(g) (Slow) H(g) + Br2(g) → HBr(g) + Br(g) (Fast)?
Problem 113
- What rate law corresponds to the proposed mechanism for the formation of hydrogen iodide, which can be written in simplified form as: I2 Δk1k-1 2I (Fast), I + H2 Δk2k-2 H2I (Fast), H2I + I ¡k3 2HI (Slow)?
Problem 114
Problem 115
A certain substance X decomposes. Fifty percent of X remains after 100 minutes. How much X remains after 200 minutes if the reaction order with respect to X is (c) second order?
Problem 116
The half-life for radioactive decay (a first-order process) of plutonium- 239 is 24,000 years. How many years does it take for one mole of this radioactive material to decay until just one atom remains?
- The energy of activation for the decomposition of 2 mol of HI to H2 and I2 in the gas phase is 185 kJ. The heat of formation of HI(g) from H2(g) and I2(g) is -5.65 kJ/mol. Find the energy of activation for the reaction of 1 mol of H2 and 1 mol of I2 to form 2 mol of HI in the gas phase.
Problem 117
- Ethyl chloride vapor decomposes by the first-order reaction: C2H5Cl -> C2H4 + HCl. The activation energy is 249 kJ/mol, and the frequency factor is 1.6 * 10^14 s^-1. Find the temperature at which the rate of the reaction would be twice as fast.
Problem 118
Problem 118b
Ethyl chloride vapor decomposes by the first-order reaction: C2H5Cl → C2H4 + HCl The activation energy is 249 kJ/mol, and the frequency factor is 1.6⨉1014 s-1. What fraction of the ethyl chloride decomposes in 15 minutes at this temperature?