Ch.15 - Chemical Equilibrium
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- At 45 °C, Kc = 0.619 for the reaction N2O4(g) ⇌ 2 NO2(g). If 46.0 g of N2O4 is introduced into an empty 2.00-L container, what are the partial pressures of NO2 and N2O4 after equilibrium has been achieved at 45 °C?
Problem 112
- When 9.25 g of ClF3 was introduced into an empty 2.00-L container at 700.0 K, 19.8% of the ClF3 decomposed to give an equilibrium mixture of ClF3, ClF, and F2. ClF3 (g) ⇌ ClF (g) + F2 (g). (a) What is the value of the equilibrium constant Kc at 700.0 K? (b) What is the value of the equilibrium constant Kp at 700.0 K? (c) In a separate experiment, 39.4 g of ClF3 was introduced into an empty 2.00-L container at 700.0 K. What are the concentrations of ClF3, ClF, and F2 when the mixture reaches equilibrium?
Problem 113
- The reaction of fumarate with water to form L-malate is catalyzed by the enzyme fumarase; Kc = 3.3 at 37°C. When a reaction mixture with [fumarate] = 1.56 * 10-3 M and [l -malate] = 2.27 * 10-3 M comes to equilibrium in the presence of fumarase at 37 °C, what are the equilibrium concentrations of fumarate and L-malate? (Water can be omit- ted from the equilibrium equation because its concentration in dilute solutions is essentially the same as that in pure water.)
Problem 115
- Calculate the equilibrium concentrations of SO2, Cl2, and SO2Cl2 at 298 K if the initial concentrations are [SO2] = 1.50 M and [Cl2] = 0.85 M. The equilibrium constant Kc for the reaction SO2(g) + Cl2(g) ⇌ SO2Cl2(g) is 8.40 × 10^-3 at 298 K.
Problem 116
- Calculate the equilibrium concentrations of H2O(g), Cl2(g), HCl(g), and O2(g) at 298 K if the initial concentrations are [H2O] = 0.050 M and [Cl2] = 0.100 M. The equilibrium constant Kc for the reaction H2O(g) + Cl2(g) ⇌ 2 HCl(g) + O2(g) is 8.96 × 10^-9 at 298 K.
Problem 117
Problem 118a,b
Consider the following equilibrium: Ag+ (aq) + Cl-(aq) → AgCl(s) Use Le Châtelier's principle to predict how the amount of solid silver chloride will change when the equilibrium is disturbed by: (a) Adding NaCl (b) Adding AgNO3
Problem 118c
Consider the following equilibrium: Ag+ (aq) + Cl-(aq) → AgCl(s) Use Le Châtelier's principle to predict how the amount of solid silver chloride will change when the equilibrium is disturbed by: (c) Adding NO3, which reacts with Ag+ to form the complex ion Ag(NH3)2+
Problem 118d
Consider the following equilibrium: Ag+(aq) + Cl-(aq) ⇌ AgCl(s) Use Le Châtelier's principle to predict how the amount of solid silver chloride will change when the equilibrium is disturbed by: (d) Removing Cl-; also account for the change using the reaction quotient Qc
- Will the concentration of NO2 increase, decrease, or remain the same when the equilibrium NO2Cl(g) + NO(g) ⇌ NOCl(g) + NO2(g) is disturbed by the following changes? (a) Adding NOCl (b) Adding NO (c) Removing NO (d) Adding NO2Cl; also account for the change using the reaction quotient Qc
Problem 119
- For the water–gas shift reaction CO1g2 + H2O1g2 ∆ CO21g2 + H21g2, ΔH° = - 41.2 kJ does the amount of H2 in an equilibrium mixture increase or decrease when the temperature is increased? How does Kc change when the temperature is decreased? Justify your answers using Le Châtelier's principle.
Problem 122
- Consider the exothermic reaction CoCl 2-1aq2 + 6 H O1l2 ∆ Co1H O2 2 + 1aq2 + 4 Cl-1aq2 which interconverts the blue CoCl 2- ion and the pink Co 2 +CoCl 2- increase or decrease when the following changes occur?(c) The solution is diluted with water.
Problem 124
- Consider the endothermic reaction Fe³⁺(aq) + Cl⁻(aq) ⇌ FeCl₂⁺(aq). Use Le Châtelier’s principle to predict how the equilibrium concentration of the complex ion FeCl₂⁺ will change when: (a) Fe(NO₃)₃ is added. (b) Cl⁻ is precipitated as AgCl by addition of AgNO₃. (d) A catalyst is added.
Problem 125
- Methanol (CH3OH) is manufactured by the reaction of carbon monoxide with hydrogen in the presence of a Cu/ZnO/Al2O3 catalyst: CO(g) + 2H2(g) ⇌ CH3OH(g) ΔH° = -91 kJ. Does the amount of methanol increase, decrease, or remain the same when an equilibrium mixture of reactants and products is subjected to the following changes? (a) The temperature is increased. (b) CO is added. (c) Helium is added. (d) The catalyst is removed.
Problem 126
- In the gas phase at 400 °C, isopropyl alcohol (rubbing alcohol) decomposes to acetone, an important industrial solvent: \[ \text{Isopropyl alcohol: }(\text{CH}_3)_2\text{CHOH(g)} \rightleftharpoons (\text{CH}_3)_2\text{CO(g) + H}_2\text{(g)} \\ \Delta H^\circ = + 57.3 \text{ kJ} \] Does the amount of acetone increase, decrease, or remain the same when an equilibrium mixture of reactants and products is subjected to the following changes? (c) Argon is added. (d) H₂ is added. (e) A catalyst is added.
Problem 127
- The following reaction is important in gold mining: 4 Au1s2 + 8 CN-1aq2 + O21g2 + 2 H2O1l2 ∆ 4 Au1CN22-1aq2 + 4 OH-1aq2For a reaction mixture at equilibrium, in which direction would the reaction go to reestablish equilibrium after each of the following changes? (a) Adding gold
Problem 128
- For the following reaction catalyzed by iridium, which is endothermic at 700 K: CaO(s) + CH₄(g) + 2 H₂O(g) ⇌ CaCO₃(s) + 4 H₂(g), how would the following changes affect the total quantity of CaCO₃ in the reaction mixture once equilibrium is reestablished at 700 K? (a) Increasing the temperature (b) Adding calcium oxide (c) Removing methane (CH₄) (d) Adding iridium.
Problem 129
- The equilibrium constant Kp for the reaction PCl51g2 ∆ PCl31g2 + Cl21g2 is 3.81 * 102 at 600 K and 2.69 * 103 at 700 K. (b) How are the equilibrium amounts of reactants and products affected by (iii) addition of a catalyst?
Problem 130
- 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
- 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
- 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