EQUILIBRIUM FREE RESPONSE QUESTION #2

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1 EQUILBRIUM FREE RESPONSE QUESTION #1 Answer the following questions relating to the solubilities of two silver compounds, Ag 2 CrO 4 and Ag 3 PO 4. Silver chromate dissociates in water according to the equation shown below: Ag 2 CrO 4 (s) -- 2Ag + (aq) + CrO 4 2- (aq) K sp = 2.6 X at 25 o C Write the equilibrium constant expression for the dissolving of Ag 2 CrO 4 (s). Calculate the concentration, in mol L -1, of Ag + (aq) in a saturated solution of Ag 2 CrO 4 at 25 o C. Calculate the maximum mass, in grams of Ag 2 CrO 4 that can dissolve in 100. ml of water at 25 o C. A mol sample of solid AgNO 3 is added to a 1.00 L saturated solution of Ag 2 CrO 4. Assuming no volume change, does [CrO 2-4 ] increase, decrease, or remain the same? Justify your answer. In a saturated solution of Ag 3 PO 4 at 25 o C, the concentration of Ag + (aq) is 5.3 X 10-5 M. The equilibrium constant expression for the dissolving of Ag 3 PO 4 (s) in water is shown below: K sp = [Ag + ] 3 [PO 3-4 ] (e) Write the balanced equation for the dissolving of Ag 3 PO 4 in water. (f) Calculate the value of K sp for Ag 3 PO 4 at 25 o C. (g) A 1.00 L sample of saturated Ag 3 PO 4 solution is allowed to evaporate at 25 o C to a final volume of 500. ml. What is [Ag + ] in the solution? Justify your answer. NO FREE RESPONSE QUESTION #2 The gas-phase conversion reaction between the geometric isomers cis-2-butene and trans-2- butene is represented by the equation above. The value of the equilibrium constant, K eq, for the reaction is 3.2 at 298 K and 1.0 atm. In a mixture of the isomers at equilibrium at 298 K and 1.0 atm, which is present at a high concentration, cis-2-butene or trans-2-butene? Justify your answer.

2 If 1.00 mol of pure cis-2-butene and 1.0 mol of pure trans-2-butene were introduced into an evacuated container at 298 K, in which direction (to the right or to the left) would the reaction proceed to establish equilibrium? Justify your answer. Given that K eq for the reaction at 400 K has the value of 1.3, predict whether the reaction is endothermic or exothermic. Justify your answer. There are other structure isomers of cis-2-butene and trans-2-butene. Draw one of these isomers, including all atoms, and give its IUPAC name. EQUILBRIUM FREE RESPONSE QUESTION #3 N 2 (g) + 3H 2 (g) NH 3 (g) For the reaction represented above, the value of the equilibrium constant, K p, is 3.1 X 10-4 at 700. K. Write the expression for the equilibrium constant, K p, for the reaction. Assume that the initial partial pressures of the gases are as follows: P N2 = atm; P H2 = atm; and P NH3 = atm (i) Calculate the value of the reaction quotient, Q, at these conditions. (ii) Predict the direction in which the reaction will proceed at 700. K if the initial partial pressures are those given above. Justify your answer. Calculate the value of the equilibrium constant, K c, given that the value of K p for the reaction at 700. K is 3.1 X The value of K p for the reaction represented below is 8.3 X 10-3 at 700. K. NH 3 (g) + H 2 S(g) --- NH 4 HS(g) Calculate the value of K p at 700. K for each of the reactions represented below: (i) NH 4 HS(g) --- NH 3 (g) + H 2 S(g) (ii) 2H 2 S(g) + N 2 (g) + 3H 2 (g) -- 2NH 4 HS(g) FREE RESPONSE QUESTION #4 2H 2 S(g) H 2 (g) + S 2 (g) When heated, hydrogen sulfide gas decomposes according to the equation above. A 3.40 gram sample of H 2 S(g) is introduced into an evacuated rigid 1.25 L container. The sealed container is heated to 483 K, and 3.72 X 10-2 mol of S 2 (g) is present at equilibrium. Write the expression for the equilibrium constant, K c, for the decomposition reaction represented above. Calculate the equilibrium concentration, in mol L -1, of the following gases in the container at 483 K. (i) H 2 (g) (ii) H 2 S(g)

3 Calculate the value of the equilibrium constant, K c, for the decomposition reactions at 483 K. Calculate the partial pressure of S 2 (g) in the container at equilibrium at 483 K. (e) For the reaction H 2 (g) + ½ S 2 (g) --- H 2 S(g) at 483 K, calculate the value of the equilibrium constant, K c. FREE RESPONSE QUESTION #5 MgF 2 (s) ---- Mg 2+ (aq) + 2F - (aq) In a saturated solution of MgF 2 is 18 o C, the concentration of Mg 2+ is 1.21 X 10-3 molar. The equilibrium is represented by the equation above. Write the expression for the solubility product constant, K sp, and calculate its value at 18 o C. Calculate the equilibrium concentration of Mg 2+ in liter of saturated MgF 2 solution is 18 o C to which mole of solid KF has been added. The KF dissolves completely. Assume the volume change is negligible. Predict whether a precipitate of MgF 2 will form when milliliters of 3.00 X 10-3 molar Mg(NO 3 ) 2 solution is mixed with milliliters of a 2.00 X 10-3 molar NaF solution at 18 o C. Calculations to support you prediction must be shown. At 27 o 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 exothermic process? Give an explanation to support your conclusion. FREE RESPONSE QUESTION #6 Answer the following questions relating to the solubility of the chlorides of silver and lead. At 10 o C, 8.9 X 19-5 g of AgCl(s) will dissolve in 100. ml of water. (i) Write the equation for the dissociation of AgCl(s) in water. (ii) Calculate the solubility, in mol L -1, of AgCl(s) in water at 10 o C. (iii) Calculate the value of the solubility product constant, K sp, for AgCl(s) at 10 o C. At 25 o C, the value for K sp for PbCl 2 (s) is 1.6 X 10-5 and the value of K sp for AgCl(s) is 1.8 X (i) If 60.0 ml of M NaCl(aq) is added to 60.0 ml of M Pb(NO 3 ) 2 (aq) at 25 o C, will a precipitate form? Assume that volumes are additive. Show calculations to support your answer. (ii) Calculate the equilibrium value of [Pb 2+ (aq)] in 1.00 L of saturated PbCl 2 solution to which mole of NaCl(s) has been added. Assume that no volume change occurs. (iii) If M NaCl(aq) is added slowly to a beaker containing both M AgNO 3(aq) and M Pb(NO 3 ) 2 (aq) at 25 o C, which will precipitate first, AgCl(s) or PbCl 2 (s)? Show calculations to support your answer.

4 FREE RESPONSE QUESTION #7 NO C(s) + H 2 O(g) -- CO(g) + H 2 (g) H o = +131 kj A rigid container holds a mixture of graphite pellets (C(s)), H 2 O(g), CO(g), and H 2 (g) at equilibrium. State whether the number of moles of CO(g) in the container will increase, decrease, or remain the same after each of the following disturbances is applied to the original mixture. For each case, assume that all other variables remain constant except for the given disturbance. Explain each answer with a short statement. Additional H 2 (g) is added to the equilibrium mixture at constant volume. The temperature of the equilibrium mixture is increased at constant volume The volume of the container is decreased at constant temperature. The graphite pellets are pulverized. FREE RESPONSE QUESTION #8 CO 2 (g) + H 2 (g) --- H 2 O(g) + CO(g) 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 2 O] = [CO] = 0.55 mol/l What is the mole fraction of CO(g) in the equilibrium mixture? Using the equilibrium concentrations given above, calculate the value of K c, the equilibrium constant, for the reaction. Determine K p in terms of K c for this system. When the system is cooled from 2,000 K to a lower temperature, 30.0 percent of the CO(g) is converted back to CO 2 (g). Calculate the value of K c at this lower temperature. (e) 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 L reaction vessel at 2,000 K. Calculate the equilibrium concentration, in moles per liter, of CO(g) at this temperature.

5 FREE RESPONSE QUESTION #9 NO NH 4 HS(s) ---- NH 3 (g) + H 2 S(g) H o = +93 kj The equilibrium above is established by placing solid NH 4 HS in an evacuated container at 25 o+c. At equilibrium, some solid NH 4 HS remains in the container. Predict and explain each of the following. The effect on the equilibrium partial pressure of NH 3 gas when additional solid NH 4 HS is introduced into the container. The effect on the equilibrium partial pressure of NH 3 gas when additional solid H 2 S is introduced into the container. The effect on the mass of solid NH 4 HS present when the volume of the container is decreased. The effect on the mass of solid NH 4 HS present when the temperature is increased.