16. Chemical Equilibrium
- Multiple Choice
Which one of the following statements does not describe the equilibrium state?
a. While at equilibrium, a dynamic process is still occurring.
b. The concentration of the reactants is equal to the concentration of the products.
c. The concentration of the reactants and products reach a constant level.
d. At equilibrium, the net concentration of all species is not changing.
e. All are true.17802
- Multiple Choice
The decomposition of nitrogen monoxide can be achieved under high temperatures to create the products of nitrogen and oxygen gas.
6 NO(aq) ⇌ 3 N2(aq) + 3 O2(aq)
a) What is the equilibrium equation for the reaction above?
b) What is the equilibrium expression for the reverse reaction.97734
- Textbook QuestionThe following diagrams represent a hypothetical reaction A ¡ B, with A represented by red spheres and B represented by blue spheres. The sequence from left to right represents the system as time passes. Does the system reach equilibrium? If so, in which diagram(s) is the system in equilibrium? [Sections 15.1 and 15.2]156
- Textbook QuestionThe following diagram represents a reaction shown going to completion. Each molecule in the diagram represents 0.1 mol, and the volume of the box is 1.0 L. (d) Assuming that all of the molecules are in the gas phase, calculate n, the change in the number of gas molecules that accompanies the reaction. [Section 15.2]53
- Textbook QuestionThe concept of chemical equilibrium is very important. Which one of the following statements is the most correct way to think about equilibrium? (a) If a system is at equilibrium, nothing is happening. (b) If a system is at equilibrium, the rate of the forward reaction is equal to the rate of the back reaction. (c) If a system is at equilibrium, the product concentration is changing over time.497
- Textbook QuestionEthene 1C2H42 reacts with halogens 1X22 by the following reaction: C2H41g2 + X21g2 Δ C2H4X21g2 The following figures represent the concentrations at equilibrium at the same temperature when X2 is Cl2 (green), Br2 (brown), and I2 (purple). List the equilibria from smallest to largest equilibrium constant. [Section 15.3]52
- Textbook QuestionEthene (C2H4) can be halogenated by this reaction: C2H4(g) + X2(g) ⇌ C2H4X2(g) where X2 can be Cl2 (green), Br2 (brown), or I2 (purple). Examine the three figures representing equilibrium concentrations in this reaction at the same temperature for the three different hal- ogens. Rank the equilibrium constants for the three reactions from largest to smallest.137
- Textbook QuestionA chemist trying to synthesize a particular compound attempts two different synthesis reactions. The equilibrium constants for the two reactions are 23.3 and 2.2 * 104 at room temperature. However, upon carrying out both reactions for 15 minutes, the chemist finds that the reaction with the smaller equilibrium constant produces more of the desired product. Explain how this might be possible.539
- Textbook QuestionThe equilibrium 2 NO1g2 + Cl21g2 Δ 2 NOCl1g2 is established at 500 K. An equilibrium mixture of the three gases has partial pressures of 0.095 atm, 0.171 atm, and 0.28 atm for NO, Cl2, and NOCl, respectively. (b) If the vessel has a volume of 5.00 L, calculate Kc at this temperature.791
- Textbook QuestionPhosphorus trichloride gas and chlorine gas react to form phosphorus pentachloride gas: PCl31g2 + Cl21g2 Δ PCl51g2. A 7.5-L gas vessel is charged with a mixture of PCl31g2 and Cl21g2, which is allowed to equilibrate at 450 K. At equilibrium the partial pressures of the three gases are PPCl3 = 0.124 atm, PCl2 = 0.157 atm, and PPCl5 = 1.30 atm. (a) What is the value of Kp at this temperature?220
- Textbook QuestionConsider the interconversion of A molecules (red spheres) and B molecules (blue spheres) according to the reaction A ∆ B. Each of the series of pictures at the right represents a separate experiment in which time increases from left to right: (b) What is the value of the equilibrium constant Kc for the reaction A ∆ B?51
- Textbook QuestionIdentify the true statement about the rate of the forward and reverse reaction once a reaction has reached equilibrium. (a) The rate of the forward reaction and the reverse reaction is zero. (b) The rate of the forward reaction is greater than the rate of the reverse reaction. (c) The rate of the reverse reaction is greater than the rate of the forward reaction. (d) The rate of the forward reaction is equal to the rate of the reverse reaction.328
- Textbook QuestionCarbon monoxide replaces oxygen in oxygenated hemoglobin according to the reaction: HbO2(aq) + CO(aq) ⇌ HbCO(aq) + O2(aq) a. Use the reactions and associated equilibrium constants at body temperature given here to find the equilibrium con- stant for the reaction just shown. Hb(aq) + O2(aq) ⇌ HbO2(aq) Kc = 1.8 Hb(aq) + CO(aq) ⇌ HbCO(aq) Kc = 306864
- Textbook QuestionThe value of Kc for the reaction 3 O21g2 ∆ 2 O31g2 is 1.7 * 10-56 at 25°C. Do you expect pure air at 25 °C to contain much O3 (ozone) when O2 and O3 are in equilib- rium? If the equilibrium concentration of O2 in air at 25 °C is 8 * 10-3 M, what is the equilibrium concentration of O3?51
- Textbook QuestionThe value of Kc for the reaction of acetic acid with ethanol is 3.4 at 25°C: CH3CO2H1soln2 + CH3CH2OH1soln2 ∆ Acetic acid Ethanol CH3CO2CH2CH31soln2 + H2O1soln2 Kc = 3.4 (a) How many moles of ethyl acetate are present in an equi- librium mixture that contains 4.0 mol of acetic acid, 6.0 mol of ethanol, and 12.0 mol of water at 25 °C?173
- Textbook QuestionConsider 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.63
- Textbook QuestionRefining petroleum involves cracking large hydrocar- bon 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.53
- Textbook QuestionConsider 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 1density 1.16 g>cm32 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. C10H81s2 ∆ C10H81g2 (b) How many mothballs are required to saturate the room with gaseous naphthalene?40
- Textbook QuestionConsider 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 1density 1.16 g>cm32 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. C10H81s2 ∆ C10H81g2 (a) When excess mothballs are present, how many gaseous naphthalene molecules are in the room at equilibrium?37
- Textbook QuestionConsider the reaction and the associated equilibrium constant: aA(g) ⇌ bB(g) Kc = 4.0 Find the equilibrium concentrations of A and B for each value of a and b. Assume that the initial concentration of A in each case is 1.0 M and that no B is present at the beginning of the reaction. c. a=1;b=21115
- Textbook QuestionConsider the reaction: A(g) ⇌ B(g) + C(g) Find the equilibrium concentrations of A, B, and C for each value of Kc. Assume that the initial concentration of A in each case is 1.0 M and that the reaction mixture initially contains no products. Make any appropriate simplifying assumptions. b. Kc = 0.0101538
- Textbook QuestionThe industrial solvent ethyl acetate is produced by the reac-tion of acetic acid with ethanol: CH3CO2H1soln2 + CH3CH2OH1soln2 ∆ CH3CO2CH2CH31soln2 + H2O1soln2 Ethyl acetate (b) A solution prepared by mixing 1.00 mol of acetic acid and 1.00 mol of ethanol contains 0.65 mol of ethyl ace- tate at equilibrium. Calculate the value of Kc. Explain why you can calculate K without knowing the volume of the solution.70
- Textbook QuestionConsider the hypothetical reaction A1g2 + 2 B1g2 Δ 2 C1g2, for which Kc = 0.25 at a certain temperature. A 1.00-L reaction vessel is loaded with 1.00 mol of compound C, which is allowed to reach equilibrium. Let the variable x represent the number of mol>L of compound A present at equilibrium. (e) From the plot in part (d), estimate the equilibrium concentrations of A, B, and C. (Hint: You can check the accuracy of your answer by substituting these concentrations into the equilibrium expression.)127
- Textbook QuestionAt 1000 K, the value of Kc for the reaction C1s2 + H2O1g2 ∆ CO1g2 + H21g2 is 3.0 * 10-2. Calculate the equilibrium concentrations of H2O, CO2, and H2 in a reac- tion mixture obtained by heating 6.00 mol of steam and an excess of solid carbon in a 5.00-L container. What is the molar composition of the equilibrium mixture?220
- Textbook QuestionThe equilibrium constant Kc for the reaction N21g2 + 3 H21g2 ∆ 2 NH31g2 is 4.20 at 600 K. When a quantity of gaseous NH3 was placed in a 1.00-L reaction vessel at 600 K and the reaction was allowed to reach equilibrium, the vessel was found to contain 0.200 mol of N2. How many moles of NH3 were placed in the vessel?30
- Textbook QuestionThe 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.)154
- Textbook QuestionHeavy 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>cm3.33
- Textbook QuestionRefining petroleum involves cracking large hydrocar- bon 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?27
- Textbook QuestionA 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?158
- Textbook QuestionA 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.)46
- Textbook QuestionFor the decomposition reaction PCl51g2 ∆ PCl31g2 + Cl21g2, Kp = 381 at 600 K and Kc = 46.9 at 700 K. (b) If 1.25 g of PCl5 is introduced into an evacuated 0.500-L flask at 700 K and the decomposition reaction is allowed to reach equilibrium, what percent of the PCl5 will decompose and what will be the total pressure in the flask?23
- Multiple Choice
The following data was collected for the following reaction at equilibrium
2 A (g) + 3 B (g) ⇌ C (g)
At 25 oC K is 5.2 x 10-4 and at 50 oC K is 1.7 x 10-7. Which of the following statements is true?
a) The reaction is exothermic.
b) The reaction is endothermic.
c) The enthalpy change, ΔH, is equal to zero.
d) Not enough information is given.5016
- Multiple ChoiceA container is charged with 2.00 mol of I2 and is allowed to reach equilibrium. The I2 decomposes to iodine atoms as shown in the following reaction:
I2 (g) ⇆ 2 I (g)
After the reaction reaches equilibrium, an inert gas is introduced into the container under conditions of constant volume. Which of the following would you expect to happen?5
- Textbook QuestionWhen lead(IV) oxide is heated above 300 C, it decomposes according to the following reaction PbO21s2Δ PbO1s2 + O21g2. Consider the two sealed vessels of PbO2 shown here. If both vessels are heated to 400 C and allowed to come to equilibrium, which of the following statements is true? (c) The amount of PbO2 remaining in each vessel will be the same. [Section 15.4]49
- Textbook QuestionWhen lead(IV) oxide is heated above 300 C, it decomposes according to the following reaction PbO21s2Δ PbO1s2 + O21g2. Consider the two sealed vessels of PbO2 shown here. If both vessels are heated to 400 C and allowed to come to equilibrium, which of the following statements is true? (a) There will be less PbO2 remaining in vessel A [Section 15.4]35
- Textbook QuestionWhen lead(IV) oxide is heated above 300 C, it decomposes according to the following reaction PbO21s2Δ PbO1s2 + O21g2. Consider the two sealed vessels of PbO2 shown here. If both vessels are heated to 400 C and allowed to come to equilibrium, which of the following statements is true? (b) There will be less PbO2 remaining in vessel B. [Section 15.4]50
- Textbook QuestionConsider the reaction A + B ∆ AB. The vessel on the right contains an equilibrium mixture of A molecules (red spheres), B molecules (blue spheres), and AB molecules. If the stopcock is opened and the contents of the two vessels are allowed to mix, will the reaction go in the forward or reverse direction? Explain.88
- Textbook QuestionThe following pictures represent the initial and equilibrium states for the exothermic decomposition of gaseous A mol- ecules (red) to give gaseous B molecules (blue). (b) Will the number of A molecules in the equilibrium mix- ture increase, decrease, or remain the same after each of the following changes? Explain. (3) Increasing the pressure by adding an inert gas57
- Textbook QuestionThe water–gas shift reaction CO1g2 + H2O1g2Δ CO21g2 + H21g2 is used industrially to produce hydrogen. The reaction enthalpy is H = -41 kJ. (b) Could you increase the equilibrium yield of hydrogen by controlling the pressure of this reaction? If so would high or low pressure favor formation of H2(g)?381
- Textbook QuestionCoal can be used to generate hydrogen gas (a potential fuel) by the endothermic reaction: C(s) + H2O(g) ⇌ CO(g) + H2(g) If this reaction mixture is at equilibrium, predict whether each disturbance will result in the formation of additional hydrogen gas, the formation of less hydrogen gas, or have no effect on the quantity of hydrogen gas. e. adding a catalyst to the reaction mixture573
- Textbook QuestionWhen 2.00 mol of SO2Cl2 is placed in a 2.00-L flask at 303 K, 56% of the SO2Cl2 decomposes to SO2 and Cl2 : SO2Cl21g2 Δ SO21g2 + Cl21g2 (c) According to Le Châtelier’s principle, would the percent of SO2Cl2 that decomposes increase, decrease or stay the same if the mixture were transferred to a 15.00-L vessel?161
- Textbook QuestionConsider the exothermic reaction: C2H4(g) + Cl2(g) ⇌ C2H4Cl2(g) If you were trying to maximize the amount of C2H4Cl2 produced, which tactic might you try? Assume that the reaction mixture reaches equilibrium. a. increasing the reaction volume b. removing C2H4Cl2 from the reaction mixture as it forms c. lowering the reaction temperature d. adding Cl2880
- Textbook QuestionConsider the endothermic reaction: C2H4(g) + I2(g) ⇌ C2H4I2(g) If you were trying to maximize the amount of C H I produced, 242 which tactic might you try? Assume that the reaction mixture reaches equilibrium. a. decreasing the reaction volume b. removing I2 from the reaction mixture c. raising the reaction temperature d. adding C2H4 to the reaction mixture510
- Textbook QuestionThe valuable polymer polyurethane is made by a condensa- tion reaction of alcohols (ROH) with compounds that con- tain an isocyanate group (RNCO). Two reactions that can generate a urethane monomer are shown here: (i) (ii) (c) If you wanted to promote the formation of the isocya- nate intermediate in each reaction, what could you do, using Le Châtelier’s principle?40
- Textbook QuestionAt a temperature of 700 K, the forward and reverse rate constants for the reaction 2 HI1g2 ΔH21g2 + I21g2 are kf = 1.8 * 10-3 M-1 s-1 and kr = 0.063 M-1 s-1. (b) Is the forward reaction endothermic or exothermic if the rate constants for the same reaction have values of kf = 0.097 M-1 s-1 and kr = 2.6 M-1 s-1 at 800 K?31
- Textbook QuestionFor 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.181
- Textbook QuestionThe binding of oxygen by hemoglobin in the blood involves the equilibrium reaction: HbH+(aq) + O2(aq)HbO2(aq) + H+(aq) In this equation, Hb is hemoglobin. The pH of normal human blood is highly controlled within a range of 7.35 to 7.45. Given the above equilibrium, why is this important? What would happen to the oxygen-carrying capacity of hemoglobin if blood became too acidic (a dangerous condition known as acidosis)?3647
- Textbook QuestionCarbon dioxide dissolves in water according to the equations: CO2( g) + H2O(l )H2CO3(aq) H2CO3(aq) + H2O(l)HCO3-(aq) + H3O+(aq) Carbon dioxide levels in the atmosphere have increased about 20% over the last century. Given that Earth’s oceans are exposed to atmospheric carbon dioxide, what effect might the increased CO2 be having on the pH of the world’s oceans? What effect might this change be having on the limestone structures (primarily CaCO3) of coral reefs and marine shells?2914
- Textbook QuestionBaking soda (sodium bicarbonate) decomposes when it is heated: 2 NaHCO31s2 ∆ Na2CO31s2 + CO21g2 + H2O1g2 ΔH° = + 136 kJ Consider an equilibrium mixture of reactants and products in a closed container. How does the number of moles of CO2 change when the mixture is disturbed by the following: (b) Adding water vapor297
- Textbook QuestionA 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.45
- Textbook QuestionIn 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.45
- Textbook QuestionAt 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 Br2139
- Textbook QuestionThe reaction A21g2 + B21g2 ∆ 2 AB1g2 has an equilib- rium constant Kc = 9. The following figure represents a reaction mixture that contains A2 molecules (red), B2 mol- ecules (blue), and AB molecules. What statement about the mixture is true? (LO 15.5) (a) The mixture is at equilibrium, and there will be no net shift in reaction direction. (b) The reaction will shift toward the reactants to reach equilibrium. (c) The reaction will shift toward the products to reach equilibrium. (d) More information is needed to answer this question.39
- Textbook QuestionAt 100 C, the equilibrium constant for the reaction COCl21g2 Δ CO1g2 + Cl21g2 has the value Kc = 2.19 * 10-10. Are the following mixtures of COCl2, CO, and Cl2 at 100 C at equilibrium? If not, indicate the direction that the reaction must proceed to achieve equilibrium. (a) 3COCl24 = 2.00 * 10-3 M, 3CO4 = 3.3 * 10-6 M, 3Cl24 = 6.62 * 10-6 M243
- Textbook QuestionConsider the reaction: NH4HS(s) ⇌ NH3(g) + H2S(g) At a certain temperature, Kc = 8.5 * 10 - 3. A reaction mixture at this temperature containing solid NH4HS has [NH3] = 0.166 M and [H2S] = 0.166 M. Will more of the solid form or will some of the existing solid decompose as equilibrium is reached?1619
- Textbook QuestionConsider the reaction: H2(g) + I2(g) ⇌ 2 HI(g) A reaction mixture at equilibrium at 175 K contains PH2 = 0.958 atm, PI2 = 0.877 atm, and PHI = 0.020 atm. A second reaction mixture, also at 175 K, contains PH2 = PI2 = 0.621 atm and PHI = 0.101 atm. Is the second reac- tion at equilibrium? If not, what will be the partial pressure of HI when the reaction reaches equilibrium at 175 K?1080
- Textbook QuestionNitric oxide (NO) reacts readily with chlorine gas as follows: 2 NO1g2 + Cl21g2 Δ 2 NOCl1g2 At 700 K, the equilibrium constant Kp for this reaction is 0.26. Predict the behavior of each of the following mixtures at this temperature and indicate whether or not the mixtures are at equilibrium. If not, state whether the mixture will need to produce more products or reactants to reach equilibrium. (b) PNO = 0.12 atm, PCl2 = 0.10 atm, PNOCl = 0.050 atm212
- Textbook QuestionAt 900 C, Kc = 0.0108 for the reaction CaCO31s2 Δ CaO1s2 + CO21g2 A mixture of CaCO3, CaO, and CO2 is placed in a 10.0-L vessel at 900 C. For the following mixtures, will the amount of CaCO3 increase, decrease, or remain the same as the system approaches equilibrium? (c) 30.5 g CaCO3, 25.5 g CaO, and 6.48 g CO2197
- Textbook QuestionThe following reaction, which has Kc = 0.145 at 298 K, takes place in carbon tetrachloride solution: 2 BrCl1soln2 ∆ Br21soln2 + Cl21soln2 A measurement of the concentrations shows 3BrCl4 = 0.050 M, 3Br24 = 0.035 M, and 3Cl24 = 0.030 M. (b) Determine the equilibrium concentrations of BrCl, Br1, and Cl2.20
- Textbook QuestionHalogen 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.71