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- A platinum catalyst is used in automobile catalytic convert- ers to hasten the oxidation of carbon monoxide: 2 CO1g2 + O 1g2 ∆Pt 2 CO 1g2 ΔH° = - 566 kJ Suppose that you have a reaction vessel containing an equilibrium mixture of CO1g2, O21g2, and CO21g2. Under the following conditions, will the amount of CO increase, decrease, or remain the same? (e) The pressure is increased by adding O2 gas.
Problem 132
- Consider the following gas-phase reaction: 2 Ag + Bg ⇌ Cg + Dg. An equilibrium mixture of reactants and products is subjected to the following changes: (a) A decrease in volume (b) An increase in temperature (c) Addition of reactants (d) Addition of a catalyst (e) Addition of an inert gas. Which of these changes affect the composition of the equilibrium mixture but leave the value of the equilibrium constant Kc unchanged? Which of the changes affect the value of Kc? Which affect neither the composition of the equilibrium mixture nor Kc?
Problem 133
- For the reaction A2 + 2B ∆ 2 AB, the rate of the for- ward reaction is 18 M/s and the rate of the reverse reaction is 12 M/s. The reaction is not at equilibrium. Will the reaction pro- ceed in the forward or reverse direction to attain equilibrium?
Problem 134
- Consider a general, single-step reaction of the type A + B ∆ C. Show that the equilibrium constant is equal to the ratio of the rate constants for the forward and reverse reactions, Kc = kf>kr.
Problem 136
- Which of the following relative values of kf and kr results in an equilibrium mixture that contains large amounts of reactants and small amounts of products? (a) kf 7 kr (b) kf = kr (c) kf 6 kr
Problem 137
- Consider the reaction of chloromethane with OH- in aque- ous solution: CH Cl1aq2 + OH-1aq2 ∆kf CH OH1aq2 + Cl-1aq2 At 25 °C, the rate constant for the forward reaction is 6 * 10-6 M-1 s-1, and the equilibrium constant Kc is 1 * 1016. Calculate the rate constant for the reverse reac- tion at 25 °C.
Problem 139
- In automobile catalytic converters, the air pollutant nitric oxide is converted to nitrogen and oxygen. Listed in the table are forward and reverse rate constants for the reac- tion 2 NO1g2 ∆ N21g2 + O21g2. Temperature (K) kf1M — 1 s-12 kr1M-1 s — 12 1400 0.29 1.1 * 10-6 1500 1.3 1.4 * 10-5 Is the reaction endothermic or exothermic? Explain in terms of kinetics.
Problem 140
- Forward and reverse rate constants for the reaction CO2(g) + N2(g) ⇌ CO(g) + N2O(g) exhibit the following temperature dependence: Temperature (K), kf (M-1 s-1), kr (M-1 s-1): 1200 K: kf = 9.1 * 10^-11, kr = 1.5 * 10^5; 1300 K: kf = 2.7 * 10^-9, kr = 2.6 * 10^5. Is the reaction endothermic or exothermic? Explain in terms of kinetics.
Problem 141
- Given the Arrhenius equation, k = Ae-Ea>RT, and the rela- tion between the equilibrium constant and the forward and reverse rate constants, Kc = kf>kr, explain why Kc for an exothermic reaction decreases with increasing temperature.
Problem 143
- Vinegar contains acetic acid, a weak acid that is partially dissociated in aqueous solution: CH3CO2H1aq2 ∆ H+ 1aq2 + CH3CO-1aq2 (b) What is the value of Kc if the extent of dissociation in 1.0 M CH3CO2H is 0.42%?
Problem 144
- Heavy water, symbolized D2O 1D = 2H2 finds use as a neutron moderator in nuclear reactors. In a mixture with ordinary water, exchange of isotopes occurs according to the following equation: H2O + D2O ∆ 2 HDO Kc = 3.86 at 298 K When 1.00 mol of H2O is combined with 1.00 mol of D2O, what are the equilibrium amounts of H2O, D2O, and HDO (in moles) at 298 K? Assume the density of the mixture is constant at 1.05 g>cm3.
Problem 145
Problem 146a
Refining petroleum involves cracking large hydrocarbon molecules into smaller, more volatile pieces. A simple example of hydrocarbon cracking is the gas-phase thermal decomposition of butane to give ethane and ethylene: (a) Write the equilibrium constant expressions for Kp and Kc.
Problem 146c
Refining petroleum involves cracking large hydrocarbon molecules into smaller, more volatile pieces. A simple example of hydrocarbon cracking is the gas-phase thermal decomposition of butane to give ethane and ethylene: (c) A sample of butane having a pressure of 50 atm is heated at 500 °C in a closed container at constant volume. When equilibrium is reached, what percentage of the butane has been converted to ethane and ethylene? What is the total pressure at equilibrium?
- At 1000 K, Kp = 2.1 * 106 and ΔH° = - 107.7 kJ for the reaction H21g2 + Br21g2 ∆ 2 HBr1g2. (b) For the equilibrium in part (a), each of the following changes will increase the equilibrium partial pressure of HBr. Choose the change that will cause the greatest increase in the pressure of HBr, and explain your choice. (ii) Adding 0.10 mol of Br2
Problem 147
- Consider the gas-phase decomposition of NOBr: 2 NOBr(g) ⇌ 2 NO(g) + Br2(g). (a) When 0.0200 mol of NOBr is added to an empty 1.00-L flask and the decomposition reaction is allowed to reach equilibrium at 300 K, the total pressure in the flask is 0.588 atm. What is the equilibrium constant Kc for this reaction at 300 K? (b) What is the value of Kp for this reaction at 300 K?
Problem 148
- Halogen lamps are ordinary tungsten filament lamps in which the lamp bulb contains a small amount of a halogen (often bromine). At the high temperatures of the lamp, the halogens dissociate and exist as single atoms. (c) When the WBr41g2 diffuses back toward the filament, it decomposes, depositing tungsten back onto the fila- ment. Show quantitatively that the pressure of WBr4 from part (a) will cause the reaction in part (a) to go in reverse direction at 2800 K. [The pressure of Br1g2 is still 0.010 atm.] Thus, tungsten is continually recycled from the walls of the bulb back to the filament, allow-ing the bulb to last longer and burn brighter.
Problem 149
Problem 151a
The F-F bond in F2 is relatively weak because the lone pairs of electrons on one F atom repel the lone pairs on the other F atom; Kp = 7.83 at 1500 K for the reaction F2(g) ⇌ 2 F(g). (a) If the equilibrium partial pressure of F2 molecules at 1500 K is 0.200 atm, what is the equilibrium partial pressure of F atoms in atm?
Problem 151b
The F-F bond in F2 is relatively weak because the lone pairs of electrons on one F atom repel the lone pairs on the other F atom; Kp = 7.83 at 1500 K for the reaction F2(g) ⇌ 2 F(g). (b) What fraction of the F2 molecules dissociate at 1500 K?
Problem 151c
The F-F bond in F2 is relatively weak because the lone pairs of electrons on one F atom repel the lone pairs on the other F atom; Kp = 7.83 at 1500 K for the reaction F2(g) ⇌ 2 F(g). (c) Why is the F-F bond in F2 weaker than the Cl-Cl bond in Cl2?
- When 0.500 mol of N2O4 is placed in a 4.00-L reaction vessel and heated at 400 K, 79.3% of the N2O4 decomposes to NO2. (a) Calculate Kc and Kp at 400 K for the reaction N2O4(g) ↔ 2 NO2(g).
Problem 152
Problem 153a
The equilibrium constant Kc for the gas-phase thermal decomposition of cyclopropane to propene is 1.0 ⨉105 at 500 K:
(a) What is the value of Kp at 500 K?
Problem 153c
The equilibrium constant Kc for the gas-phase thermal decomposition of cyclopropane to propene is 1.0 * 105 at 500 K:
(c) Can you alter the ratio of the two concentrations at equilibrium by adding cyclopropane or by decreasing the volume of the container? Explain.
- Acetic acid tends to form dimers, 1CH3CO2H22, because of hydrogen bonding: The equilibrium constant Kc for this reaction is 1.51 * 10^2 in benzene solution but only 3.7 * 10^-2 in water solution. Why is Kc for the water solution so much smaller than Kc for the benzene solution?
Problem 154
Problem 154a
Acetic acid tends to form dimers, (CH3CO2H2), because of hydrogen bonding: The equilibrium constant Kc for this reaction is 1.51⨉102 in benzene solution but only 3.7⨉10-2 in water solution. (a) Calculate the ratio of dimers to monomers for 0.100 M acetic acid in benzene.
Problem 154b
Acetic acid tends to form dimers, (CH3CO2H2), because of hydrogen bonding: The equilibrium constant Kc for this reaction is 1.51⨉102 in benzene solution but only 3.7⨉10-2 in water solution. (b) Calculate the ratio of dimers to monomers for 0.100 M acetic acid in water.
- A 125.4 g quantity of water and an equal molar amount of carbon monoxide were placed in an empty 10.0-L vessel, and the mixture was heated to 700 K. At equilibrium, the partial pressure of CO was 9.80 atm. The reaction is CO(g) + H2O(g) ⇌ CO2(g) + H2(g). (a) What is the value of Kp at 700 K? (b) An additional 31.4 g of water was added to the reaction vessel, and a new state of equilibrium was achieved. What are the equilibrium partial pressures of each gas in the mixture? What is the concentration of H2 in molecules/cm³?
Problem 155
- A 79.2 g chunk of dry ice (solid CO2) and 30.0 g of graphite (carbon) were placed in an empty 5.00-L container, and the mixture was heated to achieve equilibrium. The reaction is CO 1g2 + C s ∆ 2 CO g (b) What is the value of Kp at 1100 K if the gas density at 1100 K is 16.9 g/L?
Problem 156
- The amount of carbon dioxide in a gaseous mixture of CO2 and CO can be determined by passing the gas into an aqueous solution that contains an excess of Ba(OH)2. The CO2 reacts, yielding a precipitate of BaCO3, but the CO does not react. This method was used to analyze the equilibrium composition of the gas obtained when 1.77 g of CO2 reacted with 2.0 g of graphite in a 1.000-L container at 1100 K. The analysis yielded 3.41 g of BaCO3. Use these data to calculate Kp at 1100 K for the reaction CO2(g) + C(s) ⇌ 2 CO(g).
Problem 157
- A 14.58 g quantity of N2O4 was placed in a 1.000-L reaction vessel at 400 K. The N2O4 decomposed to an equilibrium mix- ture of N2O4 and NO2 that had a total pressure of 9.15 atm. (b) How much heat (in kilojoules) was absorbed when the N2O4 decomposed to give the equilibrium mixture? (Stan- dard heats of formation may be found in Appendix B.)
Problem 158
Problem 159a
Consider the sublimation of mothballs at 27 °C in a room having dimensions 8.0 ft ⨉ 10.0 ft ⨉ 8.0 ft. Assume that the mothballs are pure solid naphthalene (density 1.16 g/cm3) and that they are spheres with a diameter of 12.0 mm. The equilibrium constant Kc for the sublimation of naphthalene is 5.40⨉10-6 at 27 °C. C10H8(s) ⇌ C10H8(g) (a) When excess mothballs are present, how many gaseous naphthalene molecules are in the room at equilibrium?