Name period AP Unit 8: equilibrium 1. What is equilibrium? Rate of the forward reaction equals the rate of the reverse reaction 2. How can you tell when equilibrium has been reached? The concentrations of the reactants and products don t change. 3. What is the only factor that can change the value of K c? temperature 4. Write the equilibrium expression for the following reactions. a. H 2(g) + Cl 2(g) 2HCl(g) [HCl] 2 / [H 2][Cl 2] c. 2NO(g) + O 2(g) 2NO 2(g) [NO 2] 2 / [NO] 2 [O 2] b. 4NH 3(g) + 7O 2(g) 4NO 2(g) + 6H 2O (g) d. 2N 2O 5(g) 4NO 2(g) +O 2(g) [H 2O] 6 [NO 2] 4 / [O 2] 7 [NH 3] 4 [NO 2] 4 [O 2] / [N 2O 5] 2 f. FeO(s) + H 2(g) Fe(s) + H 2O (g) g. 4HCl (g) + O 2(g) 2H 2O(l) + 2Cl(g) [H 2O]/ [H 2] [Cl] 2 /[HCl] 4 [O 2] 5. When the following reactions come to equilibrium, does the equilibrium mixture contain mostly reactants or mostly products? a. N 2 + O 2 2NO; K c= 1.5 x 10-10 reactants b. 2SO 2 + O 2 H 2O + 2SO 3; K c =2.5 x 10 9 products 6. The equilibrium constant for this reaction 2SO 3(g) 2SO 2(g) + O 2 (g) is K c = 2.4 x 10-3 at 200 ⁰C. a. Calculate K c for 2SO 2(g) + O 2 (g) 2SO 3(g) 420 b. Does the equilibrium favor SO 2 and O 2, or does it favor SO 3 at this temperature? SO 3 7. The reaction AB 4C(g) 2 B 2 (g) + AC (g) reached equilibrium at 900 K in a 5.00 L vessel. At equilibrium, 0.084 mol of AB 4C, 0.035 mol of B 2, and 0.059 mol of AC were detected. What is the equilibrium constant (Kc) at this temperature for this reaction? Is this reaction product favored or reactant favored at equilibrium? 3.5 x 10-5 Reactant favored 8. Carbonyl bromide, COBr 2, decomposes to CO and Br 2 at 73⁰C. If you begin with 0.10 moles of COBr 2 in a 2.5 Liter flask and find that there are 0.015 moles of COBr 2 at equilibrium, calculate the equilibrium concentrations of the products. What is K C for this reaction? Is this reaction reactant-favored or product-favored at equilibrium? COBr 2 (g) CO (g) + Br 2 (g) 0.19 M Reactant favored 9. Hydrogen fluoride gas can be formed from hydrogen and fluorine gases according to the balanced equation shown below. At a specific temperature, the equilibrium constant K P for this reaction is 37.6. What are the partial pressures of all of the gases at equilibrium when the initial partial pressures of hydrogen gas and fluorine gas are 0.600 atm? H 2 (g) + F 2 (g) 2 HF (g) 0.150 atm for H 2; 0.150 atm for F 2; 0.900 atm for HF 10. Nitrogen gas reacts with oxygen gas at high temperature to make nitrogen oxides. This is a major source of air pollution from auto exhaust. At 1500 K, the equilibrium constant for the formation of nitrogen monoxide from its elements is 1.0 x 10-5. Calculate the equilibrium concentration of NO when the initial concentration of N 2 is 0.60 M and O 2 is 0.30M. 1.3 x 10-3 M 11. The equilibrium constant, Kc, for the following reaction is 5.9 x 10-3 at 250⁰C, Suppose 0.17 moles of N 2O 4(g) is placed in a 5.00 L flask. What is the equilibrium concentration of NO 2(g)? N 2O 4(g) 2 NO 2(g) 0.014 M
12. Define Reaction Quotient (Q). What is the difference between the reaction quotient and the equilibrium constant (K)? reaction quotient can have values at any time in the reaction and equilibrium constant must use values at equilibrium. Q is equal to [products]/[reactants], but not necessarily at equilibrium. Use the following information for questions 16 and 17: The formation of ammonia is an extremely important reaction worldwide for the production of fertilizers and explosives. At 200 C, the equilibrium constant, K c, is 0.65. N 2 (g) + 3 H 2 (g) 2 NH 3 (g) 13. For the reaction above, Q is found to be = 3.5 at 200 C. This means that a. More NH 3(g) must form in order to reach equilibrium. b. More N 2(g) must form in order to reach equilibrium. c. More H 2(g) must form in order to reach equilibrium. d. The reaction is at equilibrium. e. Cannot tell from the information given. 14. After this reaction runs for a while, the following concentrations are measured: [N 2] = 0.07 M, [H 2] = 0.009 M, and [NH 3] = 0.0002 M. Is the system at equilibrium? If not, in which direction will the reaction run in order to establish equilibrium? Q = 0.78 so the system is not at equilibrium; reverse reaction would run in order to reach equilibrium 15. At a certain temperature, K c for the reaction shown is 0.18. PCl 3 (g) + Cl 2 (g) PCl 5 (g) Suppose a reaction vessel at this temperature contained these three gases at the following concentrations: [PCl 3] = 0.0420 M, [Cl 2] = 0.0240 M, [PCl 5] = 0.0050 M. Is the system at equilibrium? If not, which direction will the reaction have to proceed to get to equilibrium? Q = 4.9 so reaction is not at equilibrium; reaction will go in reverse to reach equilibrium 16. Consider the following equilibrium, for which H < 0: 2SO 2(g) + O 2(g) 2SO 3(g) How will each of the following affect an equilibrium mixture of the three gases? a. Oxygen gas is added to the system more products b. The reaction mixture is heated more reactants c. The volume of the reaction vessel is doubled more reactants d. A catalyst is added to the mixture no change e. A noble gas is added no change f. Sulfur dioxide gas is removed from the system more reactants 17. For the following reaction, H = 2816 kj: 6CO 2(g) + 6H 2O(l) C 6H 12O 6(S) + 6O 2(g) How is the equilibrium yield of C 6H 12O 6 affected by a. Increasing the pressure of carbon dioxide increase b. Increasing the temperature more c. Decreasing the total pressure no change d. Removing carbon dioxide less e. Adding a catalyst no change f. no change 18. How do the following changes affect the value of the equilibrium constant for an exothermic reaction: a. Removal of a reactant or product no change b. Decrease in the volume no change c. Decrease in the temperature increases d. Addition of a catalyst no change
19. Predict the effect of decreasing the temperature on the position (forward or reverse) of the following equilibrium. a. 2NH 3(g) N 2(g) + 3H 2(g) Δ H = 37.2 kj reverse b. CO(g) + H 2O(g) CO 2(g) + H 2(g) Δ H = -27.6 kj forward 20. For the reaction below, which change would cause the equilibrium to shift toward the product? CH 4(g) + 2H 2S(g) + heat CS 2(g) + 4H 2(g) a. Decrease the concentration of dihydrogen sulfide. b. Increase the temperature of the system. c. Increase the concentration of carbon disulfide. d. Decrease the concentration of methane (CH 4). CO 2(g) + H 2(g) H 2O(g) + CO(g) 21. When H 2(g) is mixed with CO 2(g) at 2,000 K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured. [H 2] = 0.20 mol/l [CO 2] = 0.30 mol/l [H 2O] = [CO]= 0.55 mol/l (a) Using the equilibrium concentrations given above, calculate the value of K c, the equilibrium constant for the reaction. 5.0 (b) (c) In a different experiment, 0.50 mole of H 2(g) is mixed with 0.50 mole of CO 2(g) in a 3.0-liter reaction vessel at 2,000 K. Calculate the equilibrium concentration, in moles per liter, of CO(g) at this temperature. 0.11 M 2 H2S(g) 2 H2(g) + S2(g) 22. When heated, hydrogen sulfide gas decomposes according to the equation above. A 3.40 g sample of H2S(g) is introduced into an evacuated rigid 1.25 L container. The sealed container is heated to 483 K, and 3.72 10 2 mol of S2(g) is present at equilibrium. (a) Write the expression for the equilibrium constant, Kc, for the decomposition reaction represented above. K = [H 2] 2 [S 2]/[H 2S] 2 (b) Calculate the equilibrium concentration, in mol L -1, of the following gases in the container at 483 K. (i) H2(g) 0.0595 M (ii) H2S(g) 0.0203 M (c) Calculate the value of the equilibrium constant, Kc, for the decomposition reaction at 483 K. 0.256 23. Write the Ksp expression for these compounds. a. AgI b. Al(OH) 3 c. ZnCO 3 d. Zn(OH) 2 Ksp = [Ag][I] Ksp = [Al][OH] 3 Ksp = [Zn][CO 3] Ksp = [Zn][OH] 2 24. A saturated solution of silver chloride contains 1.94 x 10-4 g of AgCl dissolved in 100 ml of water at 20 C. Write the equilibrium constant expression for this reaction and calculate the equilibrium constant (Ksp) for AgCl. Ksp = [Ag][Cl]; 1.83 x 10-10 25. If the molar solubility of CaF 2 at 35⁰C is 1.24 x 10-3 mol/l, what is the Ksp at this temperature? 7.60 x 10-9 26. The Ksp for calcium fluoride (CaF 2) is Ksp = 4.2 x 10-11 at 25 C. What is the solubility of CaF 2 at this temperature? (In other words, what is the molarity of CaF 2 in a saturated solution?) 0.00022 M
27. A 1.00 L solution saturated at 25⁰C with calcium oxalate is evaporated to dryness, giving a 0.0061 g residue of calcium oxalate. Calculate Ksp for this salt at 25 ⁰C. 2.3 x 10-9 28. Calculate the molar solubility of AgBr in (Ksp = 5.0 x 10-13 ) a) pure water b) 0.03 M AgNO 3 solution c) 0.10 M NaBr solution 7.1 x 10-7 M 1.7 x 10-11 M 5.0 x 10-12 M 29. Calculate the molar solubility of CaF 2 in (Ksp = 3.9 x 10-11 ) a) pure water b) 0.15 M KF solution c) 0.080M Ca(NO 3) 2 solution 2.1 x 10-4 M 1.7 x 10-9 M 1.1 x 10-5 M 30. Will silver sulfate precipitate when 100 ml of 0.050 M silver nitrate is mixed with 10 ml of 5.0 x 10-2 M sodium sulfate solution? (Ksp for silver sulfate = 1.5 x 10-5 ) Q = 9.1x10-6 Q < Ksp so no precipitate 31. A solution contains 2.0 x 10-4 M Ag + and 1.5 x 10-3 M Pb 2+. If NaI is added, will AgI (K sp = 8.3 x 10-17 ) or PbI 2 (K sp = 7.9 x 10-9 ) precipitate first? Specify the concentration of I - needed to begin precipitation. AgI will precipitate first at [I - ] = 4.2 x 10-13 M 32. a. The Ksp for AgCl is 1.8 x 10-10. If Ag + and Cl - are both in solution and in equilibrium with AgCl. What is [Ag + ] If [Cl - ] =0.020 M? 9 x 10-9 M 33. Will a precipitate of lead (II) sulfate form if 100 ml of a 1.0x10-3 mol/l solution of lead (II) nitrate is added to 100 ml of 2.0x10-3 mol/l magnesium sulfate solution? (Ksp for lead sulfate = 6.3 x 10-7 ) Q = 5.0 x 10-7 Q < Ksp so no precipitate 34. In a saturated solution of MgF 2 at 18 C, the concentration of Mg 2+ is 1.21 x 10 3 molar. The equilibrium is represented by the equation above a) Write the expression for the solubility-product constant, K sp, and calculate its value at 18 C. K sp = [Mg 2+ ][F ] 2 = (1.21 x 10 3) (2 x 1.21 x 10 3) 2 = 7.09 x 10 9 b) Calculate the equilibrium concentration of Mg 2+ in 1.000 liter of saturated MgF 2 solution at 18 C to which 0.100 mole of solid KF has been added. The KF dissolves completely. Assume the volume change is negligible. K sp = [Mg 2+ ] (2x + 0.100) 2 since 2x is much less than 0.100= 7.09 x 10 9 = [Mg 2+ ] (0.010) 2 [Mg 2+ ] = (7.09 x 10 9) / (10 2) = 7.09 x 10 7 M Note: OK if 0.102 is used for [F ], then K sp = 6.76 x 10 7 c) Predict whether a precipitate of MgF 2 will form when 100.0 milliliters of a 3.00 x 10 3 molar Mg(NO 3) 2 solution is mixed with 200.0 milliliters of a 2.00 x 10 3 molar NaF solution at 18 C. Calculations to support your prediction must be shown. [Mg 2+ ]:100.0 x 3.00 x 10 3 = 300.0 x [Mg 2+ ] [Mg 2+ ] = 1.00 x 10 3 M [F ]: 200.0 x 2.00 x 10 3 = 300.0 x [F ] [F ] = 1.33 x 10 3 M
Q = Ion Product = [Mg 2+ ] [F ] 2 = (1.00 x 10 3) (1.33 x 10 3) 2 = 1.77 x 10 9 Since Q < K sp, no precipitate will form. d) At 27 C the concentration of Mg 2+ in a saturated solution of MgF 2 is 1.17 x 10 3 molar. Is the dissolving of MgF 2 in water an endothermic or an exothermic process? Give an explanation to support your conclusion. Solubility of MgF 2 decreases with the increasing temperature, thus dissolution process is exothermic. MgF 2 ---> Mg 2+ + 2F + Q (or H) Reason: i) Increased temperature puts a stree on the system (LeChâtelier). The system will reduce the stree by shifting the equilibrium in the endothermic (left) direction. OR ii) A data supported argument such as comparing ion concentrations, calculating second K sp and giving proper interpretations Review: 37. Of the following 100 ml solutions: 0.10 M NaF, 0.10 M MgCl 2, 0.10M C 2H 5OH, 0.10 M CH 3COOH a. Which solution has the lowest electrical conductivity? Explain 0.10M C 2H 5OH; this is a nonelectrolyte there are no ions in solution 38. Consider the molecules CF 4 and SF 4 a. Draw lewis structures for each molecule b. In terms of molecular geometry, account for the fact that the CF 4 molecule is nonpolar, whereas the SF 4 molecule is polar CF 4 is tetrahedral ;all of the dipoles cancel out and the molecule is nonpolar SF 4 is see saw shape; all of the dipoles do not cancel out and the molecule is polar 39. Write a balanced net ionic equation for the following a. Liquid bromine is shaken with a 0.5M sodium iodide solution Br 2 + 2I - 2Br - + I 2 b. Nitric acid is added to a sodium carbonate solution 2H + + CO 3 2- CO 2 + H 2O 40. What is the limiting reactant If 3.5 g of Zn react with 5.6 g of sodium chloride? Sodium chloride