Equilibrium 1
UNIT 3: EQUILIBRIUM OUTCOMES All important vocabulary is in Italics and bold. Relate the concept of equilibrium to physical and chemical systems. Include: conditions necessary to achieve equilibrium. Write equilibrium law expressions from balanced chemical equations for heterogeneous and homogeneous systems. Include: mass action expression. Use the value of the equilibrium constant to explain how far a system at equilibrium has gone towards completion. Solve 4 types problems involving equilibrium constants. Determine the reaction quotient, Q, for a system. Include: stating the direction the reaction is proceeding towards equilibrium. Write solubility product (Ksp) expressions from balanced chemical equations for salts with low solubility. Solve problems involving Ksp. Use Le Chatelier s principle to predict and explain shifts in equilibrium. Include: temperature changes, pressure/volume changes, changes in reactant/product concentration, the addition of a catalyst, the addition of an inert gas Interpret concentration versus time graphs. Include: temperature changes, concentration changes, addition of a catalyst. Describe practical applications of Le Chatelier s principle. Additional KEY Terms Closed system ICE table Macroscopic Dissociation Saturated 2
COMPLETE THE FOLLOWING QUESTIONS ON EQUILIBRIUM: 1. Write the equilibrium law (mass action expression) for each of the following reactions: a. SO2(g) + NO2(g) SO3(g) + NO(g) b. 2 C(s) + 3 H2(g) C2H6(g) c. 3 O2(g) 2 O3(g) d. MgCO3(s) CO2(g) + 2 MgO(s) e. 2 Bi 3+ (aq) + 3 H2S(g) 2 Bi2S3(s) + 6 H + (aq) f. I2(aq) I2(s) g. Cl2(g) + PCl3(g) PCl5(g) h. I2(g) + Cl2(g) 2 ICl(g) i. 2 NO2(g) 2 NO(g) + O2(g) j. 2 SO2(g) + O2 (g) 2 SO3(g) k. Cl2(g) + PCl3(s) PCl5(g) 2. Comment on the favorability of product formation in each of the reactions. a. H2(g) + F2(g)2 HF(g) KC = 1.0 10 13 b. SO2(g) + NO2(g)NO(g) + SO3(g) KC = 1.0 10 2 c. 2 H2O(g)2 H2(g) + O2(g) KC = 6.0 10 28 3. Chemists have determined the equilibrium constants for several reactions. In which of these reactions are the products favoured over the reactants? a. KC = 1.0 10 2 b. KC = 3.5 c. KC = 0.003 d. KC = 6.0 10 4 3
ANSWER THE FOLLOWING QUESTIONS ABOUT THE EQ CONSTANT, K C : 1. The formation of ammonia from hydrogen and nitrogen occurs by the reaction below: 3 H2 (g) + N2 (g) 2 NH3 (g) Analysis of an equilibrium mixture of nitrogen, hydrogen, and ammonia contained in a 1.00 L flask at 300.0 C gives the following results: hydrogen 0.150 moles; nitrogen 0.250 moles: ammonia 0.100 moles. Calculate KC for the reaction. (11.9) 2. A mixture at equilibrium at 827 C contains 0.552 moles of CO2, 0.552 moles H2, 0.448 moles CO, and 0.448 moles of H2O in a 1.00 L container. What is the Kc constant? (0.659) CO2 (g) + H2 (g) CO (g) + H2O (g) 3. The equilibrium constant for the reaction at 755 C is 0.256. 4 H2 (g) + CS2 (g) CH4 (g) + 2 H2S (g) What is the equilibrium concentration of H2S if at equilibrium [CH4] = 0.00108 mol/l, [H2] = 0.316 mol/l, [CS2] = 0.0898 mol/l? (0.461) 4. Find the value of K if at equilibrium there is 25.0 moles of P4, 10.0 moles of H2 and 5.00 moles of PH3, in a 5.00 L container. The equation is (0.00313) P4 (g) + 6 H2 (g) 4 PH3 (g) 5. Find the value of K for the equilibrium system ZnO (s) + CO (g) Zn (s) + CO2 (g) if at equilibrium there are 3.0 moles of CO, 4.0 moles of Zn and 4.0 moles of CO2 in a 500.0 ml container. (1.3) 4
6. If K = 46.0 for H2 (g) + I2 (g) 2 HI (g) what [I2] would be in equilibrium with 0.50 mol/l HI and 0.10 mol/l H2? (0.054) 7. If K = 10.0 for N2 (g) + 3 H2 (g) 2 NH3 (g) How many moles of NH3, at equilibrium, will be in a 2.00 L container if [H2] is 0.600 mol/l and [N2] is 0.100 mol/l? (0.930) 8. Ammonia is produced according: 3 H2 (g) + N2 (g) 2 NH3 (g) What is the value of K if at equilibrium a 3.0 L flask contains 0.45 mol of hydrogen, 0.75 mol of nitrogen, and 0.30 mol of ammonia? (12) 9. Given the reaction: N2 (g) + O2 (g) 2 NO (g) An analysis of the equilibrium mixture in a 5.0 L flask gives the following results; 2.5 mol of oxygen, 3.5 mols of nitrogen, and 0.5 mol of nitrogen monoxide. What is the value of Kc? (0.029) 10. In a closed container, nitrogen and hydrogen react to produce ammonia. At equilibrium the [N2] = 2.0 x 10-4 M, [H2] = 4.0 x 10-3 M, [NH3] = 2.2 x 10-4 M. What is the Kc for the reaction? (3800) N2 (g) + H2 (g) NH3 (g) 5
11. For the given reaction of methanol, the equilibrium concentrations were found to be [CO] = 0.170 M, [H2] = 0.322, [CH3OH] = 0.0406. Find the value of Kc. CH3OH (g) CO (g) + 2 H2 (g) 12. Bromine chloride, BrCl, decomposes to form bromine and chlorine. 2 BrCl (g) Cl2 (g) + Br2 (g) At a certain temperature the equilibrium constant for the reaction is 11.1, and the equilibrium mixture contains 4.00 mol of Cl2. How many moles of Br2 and BrCl are present in the equilibrium mixture? (1.20) 13. The decomposition of hydrogen iodide to hydrogen and iodine occurs by the reaction 2 HI (g) H2 (g) + I2 (g) Hydrogen iodide is placed in a container at 450 C an equilibrium mixture contains 0.50 moles of hydrogen iodide. The equilibrium constant is 0.020 for the reaction. How many moles of iodine and hydrogen are present in the equilibrium mixture? (0.071) 6
ANSWER THE FOLLOWING QUESTIONS ON EQULIBRIUM CONCENTRATION: 1. For the gas reaction A + B AB, initially 1.0 mol of A and 1.0 mol of B were placed in a 1.0 L container. At equilibrium, the concentration of AB was 0.40 M. a) Determine the value of the equilibrium constant. b) What is the AB concentration if [A] = 1.2 M and [B] = 0.27 M? c) What is [A] if [B] = 1.7 M and [AB] = 2.0 M? (1.1, 0.36, 1.1) 2. Consider the reaction: CO2 (g) + H2 (g) CO (g) + H20 (g) Initially, 0.25 mol of water vapour and 0.20 mol of carbon monoxide are placed in a 1.00 L reaction vessel. At equilibrium, evidence shows that 0.10 mol of carbon dioxide is present. Calculate the Kc for the reaction. (1.5) 3. Consider the reaction: 2 AB (g) A2 (g) + B2 (g) 4.0 mol of AB were placed in a 2.0 L flask and were allowed to reach equilibrium. At equilibrium, it was observed that 1.0 mol of A2 was present. What is the value of Kc? (0.25) 4. Initially, 0.10 mol of NO and 0.050 mol of H2, and 0.10 mol of H20 are placed in a 1.0 L container and allowed to react. At equilibrium the [NO] = 0.062 M. Calculate the equilibrium constant, K. (Kc = 650) 2 NO (g) + 2 H2 (g) N2 (g) + 2 H20 (g) 5. In a 1 L heated reaction vessel the following concentrations were added, [SO2] = 2.0 M, [NO2] = 2.0 M. At equilibrium, [NO] = 1.3 M. Find the Kc. (3.5) SO2 (g) + NO2 (g) SO3 (g) + NO (g) 6. Given the following reaction: 2 NH3 (g) N2 (g)+ 3 H2 (g) 4.0 mol of NH3 were added to a 2.0 L flask. At equilibrium there were 2.0 mol present. Find the equilibrium concentrations for the other entities and solve for the equilibrium constant. (1.7) 7
7. Given the reaction: H2 (g) + I2 (g) 2 HI (g) One mole of hydrogen and one mole of iodine are placed in a one litre container and allowed to react. What is the value of K at equilibrium if 1.36 mols of HI are present? (18.06) 8. For the gas reaction: A + B 2 C, 0.50 mol of each A and B are placed in a 1 L container and allowed to reach equilibrium. Equilibrium concentration of C = 0.0235 M. Determine the value of Kc. (0.002) 9. Initially, enough ammonia was dissolved in water to make a 0.0124 M solution. This was left at 25ºC to reach equilibrium, at which time it was found that the [OH - ] = 4.64 x 10-4 M. Calculate the remaining concentrations at equilibrium and find the value of Kc. (0.0119, 4.46 x 10-4, 1.81 x 10-5 ) NH3 (g) + H2O(l) NH4 + (g) + 0H - (g) 10. Initially, 12.0 mol of SO3 was added to a 3.0 L reaction vessel. At equilibrium there were 3.0 mol of SO2 present. Find the value of Kc and the remaining equilibrium concentrations. (0.056) 2 SO3 (g) 2 SO2 (g)+ O2 (g) 11. Initially the concentrations of N2 and O2 are 1.8 mol/l each and there is no NO. If at equilibrium the [NO] is 2.0 mol/l, find K. (6.25) N2(g) + O2(g) 2 NO(g) 12. Find K for the reaction 2 CO(g) + O2(g) 2 CO2(g) if initially, there is 5.0 moles of CO, 10.0 moles of O2 and 1.0 mole of CO2 in a 2.0 L container and at equilibrium CO2 has a concentration of 2.5 mol/l. (6.25) 8
ANSWER THE FOLLOWING TYPE 4 QUESTIONS OF K C : 1. If 1.0 mol each of carbon dioxide and hydrogen is initially injected into a 10.0 L reaction chamber at 986ºC, what would be the concentrations of each entity at equilibrium? (Kc = 1.60) (0.043, 0.043, 0.057, 0.057) CO2 (g) + H2 (g) CO (g) + H20 (g) 2. Consider the reaction: 2 HBr H2 (g) + Br2 (g) Initially, 0.25 mol of hydrogen and 0.25 mol of bromine are placed in 500 ml reaction vessel and heated. The Kc for the reaction is 0.020. Calculate the concentrations at equilibrium. (0.78, 0.11, 0.11) 3. Given the reaction: H2 (g) + Cl2 (g) 2 HCl (g) It is determined that the Kc for the reaction is 4.4 x 10-2 at 0ºC. Initially, 1.5 mol of hydrogen and 1.5 mol of chlorine are injected into a 750 ml reaction vessel. Find the concentrations of all entities at equilibrium. (1.8, 1.8, 0.38) 4. Consider the equilibrium CO2 (g) + H2 (g) CO (g) + H20 (g) Kc = 1.60 Initially, 8.2mol of CO and 8.2mol of H2 O are placed in a 2.0L container and allowed to react. Calculate the equilibrium concentrations of CO2 and CO. (1.8, 1.8, 2.3, 2.3) 5. If the Kc for the following reaction is 3.75, and 0.80 M of each substance was placed in a reaction vessel initially, what were the equilibrium concentrations? (0.54, 0.54, 1.06, 1.06) SO2 (g) + NO2 (g) SO3 (g) + NO (g) 6. Iodine and bromine react in a closed 2.0 L container at 150ºC to produce iodine monobromide. I2 (g) + Br2 (g) 2 IBr (g) The equilibrium constant is 1.2 x 10 2. What are the equilibrium concentrations of all entities in the mixture if the container initially contained 4.0 moles of each reactant? (0.31, 0.31, 3.38) 9
7. If 0.50 mol of iodine and 0.50 mol of chlorine are initially placed into a 2.0 L reaction vessel at 25ºC, find the concentrations of all entities at equilibrium. (0.045, 0.045, 0.41) (Kc = 81.9) I2 (g) + Cl2 (g) 2 ICl (g) 8. Given the reaction: 2 HCl H2 (g) + Cl2 (g) The Kc for the reaction is 3.2 x 10-6 at 25ºC. Calculate the concentrations at equilibrium of all entities if 2.0 mol HCl is initially placed in a closed 1.0 L vessel. (1.99 M, 0.00356 M, 0.00356 M) 9. The following equation describes the formation of HI (g); H2 (g) + I2 (g) 2 HI (g) Initially, 0.40 mol of hydrogen and 0.40 mol of iodine is injected into a 500 ml reaction vessel. The temperature is then raised to 490ºC. The Kc = 46.0, determine the concentrations of all entities at equilibrium. (0.18, 0.18, 1.2) 10. In the following equilibrium:n2 (g) + O2 (g) 2 NO (g) Kc = 0.0095 Initially, 0.15 mol N2 and 0.15 mol O2 were placed in a 1.0 L container. Calculate the concentration of all species at equilibrium. (0.143 M, 0.143 M, 0.0139 M) 11. In the following reaction, the Kc = 115. Calculate the concentration of all entities at equilibrium if 4.0 mol of H2, 4.0 mol of F2, and 6.0 mol of HF are initially placed into a 2.0 L reaction vessel. (0.550, 0.550, 5.899) H2 (g) + F2 (g) 2 HF (g) 12. Consider the following reaction: H2 (g) + F2 (g) 2 HF (g) In a 1.5 L flask 3 mol of each H2, F2, and HF were added. find the equilibrium concentrations of each entity. If the value of the equilibrium constant is 1.15 x 10 2, (0.47 M, 0.47 M, 5.06 M) 13. H2(g) + Cl2(g) 2 HCl(g) A student places 2.00 mol H2 and 2.00 mol Cl2 into a 0.500 L container and the reaction is allowed to go to equilibrium at 516 C. If KC is 76.0, what are the equilibrium concentrations of H2, Cl2 and HCl? (0.75 M, 0.75 M, 6.50 M) 10
ANSWER THE FOLLOWING QUESTIONS OF THE EQUILIBRIUM CONSTANT: - Remember, calculate Q just like you would Kc: 1. 2 C(g)Kc= 25.0 For the reaction: A (s) + 2 B (g) [A] = 12.0 mol/l [B] = 2.0 mol/l [C] = 30.0 mol/l a) Is the system at equilibrium. b) Which reaction needs to be faster (favoured), forward or reverse? c) Which concentrations are increasing or decreasing? - Find Kc value using first set of values, then calculate Q with second set and compare with calculated Kc: 2. There exists an equilibrium if 5.0 moles of CO2, 5.0 moles of CO and 0.20 moles of O2 are in a 2.0 L container at 562 C. Find Kc for the reaction 2 CO (g) + O2 (g) 2 CO2 (g) Would the system be at equilibrium if [CO2] = 15.8 mol/l, [CO] = 10.0 mol/l and [O2] = 0.25 mol/l? If not, which reaction is favoured? 3. The reaction 4 NH3 (g) + 7 O2 (g) 4 NO2 (g) + 6 H2O (g) is at equilibrium when [H2O] = 0.100 mol/l, [O2] = 2.00 mol/l, [NO2] = 0.200 mol/l and [NH3] = 0.500 mol/l. If 0.75 moles of H2O, 12.0 moles of NO, 30.0 moles of O2 and 0.30 moles of NH3 are in a 3.0 L container at the same temperature, is equilibrium For the reaction: 2 SO2 (g) + O2 (g) achieved? If not, which reaction is favoured? - Complete as a Type III question first to get concentrations, then determine Qc and compare to given Kc: 4. 2 SO3 (g) Kc = 16.0 Initially, [SO2] = 5.0 mol/l, [O2] = 10.0 mol/l and [SO3] = 0. After two hours [O2] = 7.9 mol/l. Is the system at equilibrium? If not, which substances are increasing and which are decreasing? 5. K = 46.0 for the reaction H2 (g) + I2 (g) 2 HI (g) Initially there are 6.90 moles of H2 and 2.40 moles of I2 in a 1.00 L container. After 5 hours there is still 1.00 moles of I2 left. Is the system at equilibrium? If not, which substances are increasing and which are decreasing? 11
- Extra Type IV questions: 6. For the reaction: NH4Cl (s) NH3 (g) + HCl (g) Kc = 3.50 x 10-4 Find the concentration of NH3 in a 1.00 L container at equilibrium if initially there were 0.200 moles of NH3 added to 0.200 moles of HCl. (0.019) 7. H2 (g) + Cl2 (g) 2 HCl (g) A student places 2.00 mol H2 and 2.00 mol Cl2 into a 0.500 L container and the reaction is allowed to go to equilibrium at 516 C. If Kc is 76.0, what are the equilibrium concentrations of H2, Cl2 and HCl? (0.74, 0.74, 6.51) 8. If Kc = 1.00 x 10-4 for the reaction N 2 (g) + O 2 (g) 2 NO (g) Find the number of moles of NO in a 10.0 L container if the initial [N2] and [O2] is 1.00 mol/l. (9.95) 9. If Kc = 78.0 for the reaction A (s) + 2 B (g) 2 C (g) and initially there are 5.00 moles of A and 4.84 moles of B in a 2.00 L container, how many moles of B are left at equilibrium? (0.49) 10. For the reaction: C (s) + O2 (g) CO2 (g) Kc = 25.0 Find the moles of CO2 at equilibrium, if initially there are 100.0 moles of C, 50.0 moles of O2 and 2.0 moles of CO2 in a 2.00 L container. (50.0) 12
ANSWER THE FOLLOWING QUESTIONS ON SOLUBILITY EQUILIBRIA: 1. Write the dissociation equation and the solubility product expression for each of the following (assume that all the solid that dissolves exists as ions). a. PbSO4 d. SrCO3 b. Al2(SO4)3 e. Ag2CO3 c. Ba(OH)2 f. Fe2(SO4)3 2. From the following solubilities, calculate the Ksp. ** (watch units) a. Ca3(PO4)2 7.15 x 10-7 M c. AgI 2.88 x 10 6 g/l b. Pb(OH)2 4.20 x 10 6 mol/l d. CaF2 1.70 x 10-5 g/ml 3. A saturated solution of calcium hydroxide has an hydroxide ion concentration of 3.0 x 10-3 mol/l. Calculate the Ksp of calcium hydroxide. 4. At 25 C, a saturated solution of iron (III) hydroxide has an iron ion concentration of 1.3 x 10-13 mol/l. Calculate the Ksp of iron (III) hydroxide. 5. If 6.7 x 10-5 g of AgBr is all that can be dissolved at 25 C in 500.0 ml, calculate the solubility product of AgBr. 6. If [D + ] is 2.00 x 10-5 M at equilibrium, what is the Ksp for D2A? 13
7. Given the following compounds Ksp, calculate their solubilities in mol/l and g/l. a. CuS Ksp = 6.31 x 10 36 c. SrC2O4 Ksp = 1.58 x 10 7 b. PbI2 Ksp = 1.39 x 10 8 d. Al(OH)3 Ksp = 1.26 x 10 33 8. What are the equilibrium concentrations of all the ions in a saturated solution of AgSCN at 25 C, if the Ksp is 1.6 x 10-14? 9. What are the equilibrium concentrations of all the ions in a saturated solution of Cu(OH)2 at 25 C, if the Ksp is 1.6 x 10-19. 10. How many grams of each compound should be added to a 1.0 L container to have a saturated aqueous solution? a. Lead (II) sulfate, PbSO4 Ksp = 1.3 x 10-8 -12 b. Silver carbonate, Ag2CO3 Ksp = 6.2 x 10 c. Magnesium hydroxide, Mg(OH)2 Ksp = 1.2 x 10-11 11. The dissolving process of sodium acetate is endothermic. What will be observed when a warm saturated solution of sodium acetate is cooled? Explain with Le Chatelier s principle. ANSWERS 2 a) 2.02 x 10-29 b) 2.96 x 10-16 c) 1.50 x 10-16 d) 4.12 x 10-11 3) 1.35 x 10-8 4) 7.7 x 10-51 5) 5.1 x 10-13 6) 4.0 x 10-15 7 a) 2.51 x 10-18 M, 2.40 x 10-16 g/l b) 1.5 x 10-3 M, 0.698 g/l c) 3.97 x 10-4 M, 6.97 x 10-2 g/l d) 2.61 x 10-9 M, 2.04 x 10-7 g/l 8) 1.3 x 10-7 M 9) 3.4 x 10-7 M, 6.8 x 10-7 M 10) 0.0345g, 0.0317g, 0.00835g 14
ANSWER THE FOLLOWING QUESTIONS FOR Le Chatelier s Principle: 1. For the reaction: PCl3(g) + Cl2(g) PCl5(g) H = -92.5 kj Predict the effect on the position of the equilibrium that results from a) increasing the total pressure by decreasing volume. b) injecting more Cl2 gas. c) increasing the temperature. d) increasing the volume of the container. e) adding a catalyst. 2. For the reaction: CH 4(g) + H 2 O (g) + 49.3 kj CO (g) + 3 H 2(g) Predict the effect on the position of the equilibrium that results from a) increasing temperature. b) decreasing temperature. c) decreasing the pressure. d) decreasing the volume of the container. e) adding a solid drying agent such as CaCl2 which reacts with H2O(g). 3. For the reaction: 9.4 kj + 2 HI (g) H 2(g) + I 2(g) a) What is the effect on [HI] if a small amount of H2 is added? b) What is the effect on [HI] if the pressure of the system is increased? c) What is the effect on [HI] if the temperature is increased? d) What is the effect on [HI] if a catalyst is added? 4. For the reaction: CO (g) + 2 H 2(g) CH 3 OH (g) + energy Predict the effect of the following changes on the equilibrium concentration of CH3OH(g) a) a decrease in temperature. b) an increase in pressure. c) addition of H2(g). d) addition of a catalyst. 5. In the equilibrium reaction: 2 NO(g) + O2(g) 2 NO2(g) + 114.6 kj What will be the change in the equilibrium [NO2] under each of the following conditions? a) O2 is added. b) NO is removed. c) energy is added. 15
6. For the following reaction: N2O4(g) + 58.9 kj 2 NO2(g) How will the equilibrium [NO2] be affected by the following? a) an increase in pressure. b) an increase in temperature. c) the addition of a catalyst. 7. Suggest 4 ways to increase the [SO3] in the following equilibrium reaction: 2 SO2(g) + O2(g) 2 SO3(g) + 192.3 kj 8. For the reaction: 4 HCl (g) + O 2(g) 2 H 2 O (g) + 2 Cl 2(g) + 114.4 kj EXPLAIN how each of the following effect the position of the equilibrium. a) the size of the container is increased. b) energy added. c) O2(g) added. d) HCl(g) removed. e) Adding a catalyst 9. Nitric oxide gas, NO, releases 57.3 kj/mol when it reacts with oxygen gas to give nitrogen dioxide gas. a) Write the equation for this reaction. b) Predict the effect that increasing the temperature will have on i) the equilibrium concentrations. ii) the speed of formation of NO2. 16
Le Chatelier s Principle Worksheet 1. Given the reaction 2A + 3B 3C + 4 kj, which way, if any, will the equilibrium shift when the following changes are made: a. the concentration of A is increased. b. The concentration of C is increased. c. The concentration of B is increased. d. The volume of the container is decreased. e. The temperature is increased. f. Helium gas is added. 2. Given the reaction M + 2N P + T H = 15 kj What will happen to the concentration of T when the following changes are made: a. the concentration of M is decreased. b. The concentration of N is increased. c. The pressure is increased. d. The concentration of P is decreased. e. The temperature is decreased. f. A catalyst is added. 3. In the Haber process, ammonia is produced according to the reaction N2 + 3 H2 2 NH3 + heat Which way will the equilibrium shift: a. When the temperature is increased? b. When the concentration of hydrogen is decreased? c. When the concentration of ammonia is increased? d. When the concentration of nitrogen is decreased? e. If the pressure is decreased? f. What conditions of pressure, temperature, and concentration should be maintained to increase the yield of ammonia overall? 17
ANSWER THE FOLLOWING QUESTIONS ON EQUILIBRIUM GRAPHS: The above graph shows concentration versus time for a system containing carbon monoxide (CO) dichlorine (Cl2) and phosgene (COCl2). 1. Write a balanced equation to represent the reaction studied. 2. How much time was required for the system to reach equilibrium? 3. Calculate an approximate value for the equilibrium constant Kc using the concentrations at time t = 60 s. 4. Explain the changes 70 s after the initiation of the reaction. 18
5. What changes in conditions might have been imposed on the system 120 s after the initiation of the reaction? 6. Are any events taking place between the interval 50 s and 70 s? between 280 s and 300 s? Explain your answers. 7. What changes may have taken place at t = 320 s? 8. What differences would you have noticed if a catalyst had been present during the entire course of this reaction? 9. List the changes you might impose on this system if you wanted to produce a maximum amount of phosgene (COCl2)? 10. Calculate the equilibrium constant for t = 100s, 300s and 500s. How could you account for the differences in the value calculated for the equilibrium constant Kc from the concentrations at different time points on the graph? 19
ANSWER THE FOLLOWING REVIEW QUESTIONS FOR EQUILIBRIUM: 1. If 1.0 mol each of carbon dioxide and hydrogen is initially injected into a 10.0 L reaction chamber at 986ºC, what would be the concentrations of each entity at equilibrium? (Kc = 1.60) (0.044, 0.044, 0.056, 0.056) CO2 (g) + H2 (g) CO (g) + H20 (g) 2. Consider the reaction: 2 HBr (g) H2 (g) + Br2 (g) Initially, 0.25 mol of hydrogen and 0.25 mol of bromine are placed in 500 ml reaction vessel and heated. The Kc for the reaction is 0.020. Calculate the concentrations at equilibrium. (0.78, 0.11, 0.11) 3. With reference to the equation: 2 SO2 (g) + O2 (g) 2 SO 3 (g)(endothermic) a. What stresses will produce an increase in the quantity of SO3 produced, if the temperature is kept constant? b. What is the effect of a rise of temperature on the equilibrium? 4. Hydrogen peroxide can be decomposed as follows: H2O2 (l) H2 (g) + O2 (g) (exothermic) Equilibrium is established in a 10 L flask at room temperature. Predict the direction of the equilibrium shift. a. hydrogen gas is added to the flask. b. The temperature is raised to 500 ºC. c. The entire mixture is compressed into a smaller volume. 5. For the given reaction of methanol, the equilibrium concentrations were found to be [CO] = 0.170 M, [H2] = 0.322, [CH3OH] = 0.0406. Find the value of Kc. (0.434) CH3OH (g) CO (g) + 2 H2 (g) 6. Write the equilibrium constant expression for the following chemical reaction: H2 (g) + Cl2 (g) 2 HCl (g) 20
7. At 448 ºC, Kc = 50.5 for the reaction, H2 (g) + I2 (g) 2 HI (g) Find the Q and predict how the reaction proceeds if the concentration of hydrogen is 0.15 M, 0.175 M for Iodine, and 0.950 for hydrogen iodide. (34.4) 8. Define, in detail, the following terms: closed system, equilibrium, dynamic equilibrium, Le Chatelier s principle. 9. For the all-gas reaction of N2 + O2 2 NO, the equilibrium constant is 1.0 x 10-30 at room temperature, and then 0.1 at 2000ºC. Which reaction, the forward or reverse, a. Is favor at room temperature? b. Is favored at the higher temperature? c. is the forward reaction endothermic or exothermic? Explain. 10. One liter of water is able to dissolve 2.5 x 10-3 mol of PbF2. What is the Ksp for this compound? (6.2 x 10-8 ) 11. The Ksp of PbI2 is 8.3 x 10-9. What is the molar solubility of this compound in water? (1.28 x 10-3 mol/l) 12. Arrange the following ionic solids in order of decreasing solubility at room temperature, on the basis of their Ksp values: a. BaCO3 = 2 x 10-9 b. CaCO3 = 5 x 10-9 c. MgCO3 = 2 x 10-8 d. PbCO3 = 7.4 x 10-14 13. A saturated aqueous solution of barium sulfate, BaSO4, a slightly soluble ionic compound has added to it a few crystals of sodium sulfate, which is readily soluble in water. a. In terms of a shift in the position of equilibrium, describe what happens when the sodium sulfate is added to the solution. b. How will this shift affect the concentration of barium and sulfate ions? c. How will this shift affect the mass of BaSO4? 21