AP Chapter 14: Chemical Equilibrium & Ksp

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1 AP Chapter 14: Chemical Equilibrium & Ksp Warm-Ups (Show your work for credit) Name Date 1. Date 2. Date 3. Date 4. Date 5. Date 6. Date 7. Date 8.

2 AP Chapter 14: Chemical Equilibrium & Ksp 2 Warm-Ups (Show your work for credit) Date 1. Date 2. Date 3. Date 4. Date 5. Date 6. Date 7. Date 8.

3 AP Chapter 14: Chemical Equilibrium & Ksp 3 Warm-ups and problems will be collected before you take the test. Read Chapter 14: Chemical Equilibrium and Chapter : Solubility Product Answer the following problems in the space provided. For problems involving an equation, carry out the following steps: 1. Write the equation. 2. Substitute numbers and units. 3. Show the final answer with units. There is no credit without showing work. Relationship between Kinetics and Equilibrium 1. Consider the following reaction, which takes place in a single elementary step: kf 2A + B A 2B kr If the equilibrium constant K c is 12.6 at a certain temperature and if k r = 5.1 x 10-2 s -1, calculate the value of k f. Equilibrium Constant 2. Define chemical equilibrium. For a given chemical reaction, how can you tell if the reaction is at equilibrium? 3. Consider the following equilibrium process at 700 C: 2H 2(g) + S 2(g) 2H 2S(g) Analysis shows 2.50 moles of H 2, 1.35 x 10-5 mole of S 2, and 8.70 moles of H 2S present in a 12.0 L flask. a. Calculate the equilibrium constant K c for the reaction. b. Calculate K P for the reaction. c. Does the value of K c indicate that there are mostly reactants or products? 4. The equilibrium constant K P for the reaction: is 1.8 x 10-5 at 350 C. What is K c for this reaction? 2SO 3(g) 2SO 2(g) + O 2(g)

4 AP Chapter 14: Chemical Equilibrium & Ksp 4 5. At equilibrium, the pressure of the reacting mixture: CaCO 3(s) CaO(s) + CO 2(g) is atm at 350 C. Calculate K P and K c for this reaction. 6. Ammonium carbamate, NH 4CO 2NH 2, decomposes as follows: NH 4CO 2NH 2(s) 2NH 3(g) + CO 2(g) Starting with only the solid, it is found that at 40 C the total gas pressure (NH 3 and CO 2) is atm. Calculate the equilibrium constant K P. 7. Consider the reaction: 2NO(g) + O 2(g) 2NO 2(g) At 430 C, an equilibrium mixture consists of mole of O 2, mole of NO, and 0.96 mole of NO 2. Calculate K P for the reaction, given that the total pressure is 0.20 atm. 8. At a certain temperature the following reactions have the equilibrium constants shown: S(s) + O 2(g) SO 2(g) K c ' = 4.2 x S(s) + 3O 2(g) 2SO 3(g) K c = 9.8 x Calculate the equilibrium constant K c for the following reaction at that temperature: 2SO 2(g) + O 2(g) 2SO 3(g)

5 AP Chapter 14: Chemical Equilibrium & Ksp 5 What the Equilibrium Constant Tells about a Reaction 9. What is the difference between the equilibrium constant (K c) and the reaction quotient (Q)? 10. By comparing K c and Q, how can you tell if the reaction will proceed in the forward direction, reverse direction, or is at equilibrium? 11. For the synthesis of ammonia: N 2(g) + 3H 2(g) 2NH 3(g) the equilibrium constant K c at 375 C is 1.2. Starting with [H 2] o = 0.76 M, [N 2] o = 0.60 M, and [NH 3] o = 0.48 M, which gases will increase in concentration and which will decrease in concentration when the mixture comes to equilibrium? 12. Consider the following equilibrium process at 686 C: CO 2(g) + H 2(g) CO(g) + H 2O(g) The equilibrium concentrations of the reacting species are [CO] = M, [H 2] = M, [CO 2] = M, and [H 2O] = M. (a) Calculate K c for the reaction at 686 C. (b) Calculate the reaction quotient to predict what happens to the concentrations of reactant and products if CO 2 is added to the mixture at equilibrium to increase its concentration to 0.50 mol/l.

6 AP Chapter 14: Chemical Equilibrium & Ksp 6 Calculating Equilibrium Concentrations and Pressures 13. Pure phosgene gas (COC1 2), 3.00 x 10-2 mol, was placed in a 1.50 L container. It was heated to 800 K, and at equilibrium the pressure of CO was found to be atm. Calculate the equilibrium constant K P for the reaction: CO(g) + Cl 2(g) COCl 2(g) 14. Gaseous hydrogen fluoride can be prepared from its elements in the following combination reaction that has an equilibrium constant (K c) of 1.15 x 10 2 : H 2(g) + F 2(g) 2HF(g) In a particular experiment, 3.00 mol of H 2, F 2, and HF were added to a L sealed flask. (a) Does the reaction proceed in the forward direction, reverse direction, or is it at equilibrium? (b) Calculate the equilibrium concentrations of all species. 15. A 2.50 mole quantity of NOC1 was initially in a 1.50 L reaction chamber at 400 C. After equilibrium was established, it was found that 28.0 percent of the NOC1 had dissociated: 2NOCl(g) 2NO(g) + Cl 2(g) Calculate the equilibrium constant K c for the reaction.

7 AP Chapter 14: Chemical Equilibrium & Ksp At 1000 K, a 0.52 atm sample of pure NO 2 gas decomposes: 2NO 2(g) 2NO(g) + O 2(g) The equilibrium constant K P is 158. Analysis shows that the total pressure is 0.77 atm at equilibrium. Calculate the equilibrium pressure of all three gases in the mixture. LeChatelier s Principle and Factors that Affect Equilibrium 17. Heating solid sodium bicarbonate in a closed vessel establishes the following equilibrium: 2NaHCO 3(s) Na 2CO 3(s) + H 2O(g) + CO 2(g) What would happen to the equilibrium position, at constant temperature, if (a) some of the CO 2 were removed from the system? (b) some solid Na 2CO 3 were added to the system? (c) some of the solid NaHCO 3 were removed from the system? 18. Consider the following equilibrium process: PCl 5(g) PCl 3(g) + Cl 2(g) H o = 92.5 kj Predict the direction of the shift in equilibrium when: (a) the temperature is raised (b) more chlorine gas is added to the reaction mixture (c) some PC1 3 is removed from the mixture (d) the pressure on the gases is increased (e) a catalyst is added to the reaction mixture. 19. Consider the following endothermic equilibrium reaction in a closed container: CaCO 3(s) CaO(s) + CO 2(g) What will happen if (a) volume is increased? (b) some CaO is added to the mixture?

8 AP Chapter 14: Chemical Equilibrium & Ksp 8 (c) some CaCO 3 is removed? (d) some CO 2 is added to the mixture? (e) a few drops of a NaOH solution are added to the mixture? (f) a few drops of a HC1 solution are added to the mixture (ignore the reaction between CO 2 and water)? (g) temperature is increased? (Hint: calculate H rxn using standard enthalpies of formation.) Physical Equilibrium 20. What is the difference between chemical equilibrium and physical equilibrium? Give two examples of physical equilibria, with one not being a phase change. 21. The vapor pressure of mercury is mmhg at 26 C. a. Calculate K c and K P for the process: Hg(l) Hg(g). b. A chemist breaks a thermometer and spills mercury onto the floor of a laboratory measuring 6.1 m long, 5.3 m wide, and 3.1 m high. Calculate the mass of mercury (in grams) vaporized at equilibrium and the concentration of mercury vapor in mg/m 3. Does this concentration exceed the safety limit of 0.05 mg/m 3? Solubility Equilibria 22. Write the solubility product expression for the ionic compound A xb y. 23. Use BaSO 4 as an example to define the terms solubility, molar solubility, and solubility product.

9 AP Chapter 14: Chemical Equilibrium & Ksp Write solubility product expressions for the following compounds: a. CuBr b. AuCl 3 c. Mn 3(PO 4) From the solubility data given, calculate the solubility products for the following compounds: a. SrF 2, 7.3 x 10-2 g/l b. Ag 3PO 4, 6.7 x 10-3 g/l. 26. Using data from Table 16.2, calculate the molar solubility of: a. CaF 2 b. Ca 3(PO 4) As a rough guide when comparing the solubility of two salts, the one with the higher K sp is more soluble. Silver chloride has a larger K sp than silver carbonate. Does this mean that silver chloride also has a larger molar solubility than silver carbonate? Show a calculation to support your conclusion. Will a Precipitate Form? mL of M BaCl 2 are added to 600.mL of M K 2SO 4. Will a precipitate form?

10 AP Chapter 14: Chemical Equilibrium & Ksp If 2.00mL of M NaOH are added to 1.00 L of M CaCl 2, will a precipitate form? 30. A volume of 75 ml of M NaF is mixed with 25 ml of 0.15 M Sr(NO 3) 2. Calculate the concentrations of all the ions in the final solution. (K sp for SrF 2 = 2.0 x ) Common Ion Effect 31. How does the common ion effect influence solubility equilibria? Use LeChatelier s principle to explain the decrease in solubility of CaCO 3 in a Na 2CO 3 solution. 32. How many grams of CaCO 3 will dissolve in 300. ml of M Ca(NO 3) 2? 33. The solubility product of PbBr 2 is 8.9 x Determine the molar solubility: a. in pure water b. in 0.20 M KBr solution c. in 0.20 M Pb(NO 3) 2 solution.

11 AP Chapter 14: Chemical Equilibrium & Ksp 11 Review 34. Explain in terms of Coulomb s law why the first ionization energy of nitrogen is greater than that of carbon. 35. A metal ion with a +2 charge has two electrons in the 3d subshell. Identify the element. 36. A 200. g aqueous solution containing 24.0 g of hydrofluoric acid is mixed with a 200. g aqueous solution containing excess barium hydroxide in a calorimeter cup with a heat capacity of 52 J/ o C. Both solutions were at 17.0 o C prior to mixing and the final temperature of the mixture was 67.0 o C. a. What is the heat given off by the reaction? b. What is the molar enthalpy of the reaction?

12 AP Chapter 14: Chemical Equilibrium & Ksp 12 Ksp Highlights There are several common types of problems involving insoluble salts. 1. Problems where ion concentrations are controlled entirely by an insoluble salt dissolving. Example: How much SrF 2 will dissolve in water, and what is the F - concentration in a saturated SrF 2 solution? Let s be the molar solubility of SrF 2 in water. SrF2(s) Sr 2+ (aq) + 2F - (aq) s 2s Ksp = [Sr 2+ ][F - ] 2 = s(2s) 2 = 4s 3 Look up K sp (K sp = 2.0 x10-10 ) and solve for s, the molar solubility; [F - ] = 2s. 2. Problems involving the common ion effect. According the Le Chatelier s principle, addition of a common ion (an ion that is part of the equilibrium expression) to an equilibrium mixture will shift the equilibrium to the opposite side. Example: How much SrF 2 will dissolve in water that is 0.20M NaF? Since F - is a common ion, it will suppress the dissolution of SrF 2 by shifting the equilibrium to the SrF 2(s) side. SrF2(s) Sr 2+ (aq) + 2F - (aq) s 2s Since 2s is small compared to 0.20M, the expression for K sp becomes Ksp = s(0.20) 2 = 0.04s Look up K sp and solve for s, the molar solubility. The value of s will be much smaller than in pure water due to the common ion effect. 3. Problems where an insoluble salt is formed by adding two solutions. Example: When 200.mL of 1.0 x 10-4 M Sr(NO 3) 2 is mixed with 100.mL of 1.0 x 10-4 M NaF, does a precipitate form, and if so, what are the Sr 2+ and F - concentrations at equilibrium? To calculate whether a precipitate forms, calculate Q and compare to K sp. Remember the total volume is 300.mL. [Sr 2+ ]o = (.200L x 1.0E-4M) / 0.300L = 6.67E-5M [F - ]o = (.100L x 1.0E-4M) / 0.300L = 3.33E-5M Since Q > Ksp, a precipitate will form. Q = [Sr 2+ ]o[f - ]o 2 = (6.67E-5)(3.33E-5) 2 = 7.40E-4 To calculate the ion concentrations at equilibrium, set up an ICE table: SrF2(s) Sr 2+ (aq) + 2F - (aq) I 6.67E E-5 (see above) C -1.67E E-5 (F - limiting, stoich is 1:2) E 5.00E-5 ~0 (F - controlled by stoich) Look up K sp and solve for x, the F - concentration. Ksp = [Sr 2+ ][F - ] 2 = (5.0E-5) (x) 2

Chemical Equilibrium. A state of no net change in reactant & product concentrations. There is a lot of activity at the molecular level.

Chemical Equilibrium. A state of no net change in reactant & product concentrations. There is a lot of activity at the molecular level. Chemical Equilibrium A state of no net change in reactant & product concentrations. BUT There is a lot of activity at the molecular level. 1 Kinetics Equilibrium For an elementary step in the mechanism: