Unit 5 HW Packet (Chapters 13 & 16)

Unit 5 HW Packet (Chapters 13 & 16)

Gaseous Equilibrium

Section 1: Multiple Choice

1) CuO(s) + H2(g) <===> Cu(s) + H2O(g) ΔH = - 2.0 kJ/mol

When the substances in the equation above are at equilibrium at pressure P and temperature T, the equilibrium can be shifted to favor the products by

(A) increasing the pressure by means of a moving piston at constant T
(B) increasing the pressure by adding an inert gas such as nitrogen
(C) decreasing the temperature
(D) allowing some gases to escape at constant P and T
(E) adding a catalyst

2) HgO(s) + 4 I¯ + H2O  HgI42¯ + 2 OH¯ ΔH < 0

Consider the equilibrium above. Which of the following changes will increase the concentration of HgI42¯

(A) Increasing the concentration of OH¯
(B) Adding 6 M HNO3
(C) Increasing the mass of HgO present
(D) Increasing the temperature
(E) Adding a catalyst

3) In which of the following systems would the number of moles of the substances present at equilibrium NOT be shifted by a change in the volume of the system at constant temperature?

(A) CO(g) + NO(g) <===> CO2(g) + 1/2 N2(g)
(B) N2 (g) + 3 H2 (g) <===> 2 NH3(g)
(C) N2 (g) + 2 O2 (g) <===> 2 NO2(g)
(D) N2O4 (g) <===> 2 NO2(g)
(E) NO(g) + O3 (g) <===> NO2(g) + O2(g)

4) PCl3(g) + Cl2(g)  PCl5(g) + energy

Some PCl3 and Cl2 are mixed in a container at 200 °C and the system reaches equilibrium according to the equation above. Which of the following causes an increase in the number of moles of PCl5 present at equilibrium?

I. Decreasing the volume of the container
II. Raising the temperature
III. Adding a mole of He gas at constant volume

(A) I only
(B) II only
(C) I and III only
(D) II and III only
(E) I, II, and III

5) 4 HCl(g) + O2(g)  2 Cl2(g) + 2 H2O(g)

Equal numbers of moles of HCl and O2 in a closed system are allowed to reach equilibrium as represented by the equation above. Which of the following must be true at equilibrium?

I. [HCl] must be less than [Cl2].
II. [O2] must be greater than [HCl].
III. [Cl2] must equal [H2O].

(A) I only
(B) II only
(C) I and III only
(D) II and III only
(E) I, II, and III

Section 2: Free Response Questions

1. Answer the following questions regarding the decomposition of arsenic pentafluoride, AsF5(g).

(a)A 55.8 g sample of AsF5(g) is introduced into an evacuated 10.5 L container at 105°C.

(i) What is the initial molar concentration of AsF5(g) in the container?

(ii) What is the initial pressure, in atmospheres, of the AsF5(g) in the container?

At 105°C, AsF5(g) decomposes into AsF3(g) and F2(g) according to the following chemical equation.

AsF5(g)  AsF3(g) + F2(g)

(b)In terms of molar concentrations, write the equilibrium-constant expression for the decomposition of AsF5(g).

(c)When equilibrium is established, 27.7 percent of the original number of moles of AsF5(g) has decomposed.

(i) Calculate the molar concentration of AsF5(g) at equilibrium.

(ii) Using molar concentrations, calculate the value of the equilibrium constant, Keq, at 105°C.

(d)Calculate the mole fraction of F2(g) in the container at equilibrium

C(s) + CO2 (g)  2 CO(g)

Solid carbon and carbon dioxide gas at 1,160 K were placed in a rigid 2.00 L container, and the reaction represented above occurred. As the reaction proceeded, the total pressure in the container was monitored. When equilibrium was reached, there was still some C(s) remaining in the container. Results are given below.

Time (hours)Total Pressure of Gases in Container at 1,160 K (atm)

0.0 5.00

2.0 6.26

4.0 7.09

6.0 7.75

8.0 8.37

10.0 8.37

(a)Write the expression for the equilibrium constant, Kp for the reaction.

(b)Calculate the number of moles of CO2(g) initially placed in the container. (Assume that the volume of the solid carbon is negligible.)

(c)For the reaction mixture at equilibrium at 1,160 K, the partial pressure of the CO2(g) is 1.63 atm. Calculate

(i)the partial pressure of CO(g)

(ii) the value of the equilibrium constant, Kp

(d)If a suitable solid catalyst were placed in the reaction vessel, would the final total pressure of the gases at equilibrium be greater than, less than, or equal to the final total pressure of the gases at equilibrium without the catalyst? Justify your answer. (Assume that the volume of the solid catalyst is negligible.)

In another experiment involving the same reaction, a rigid 2.00 L container initially contains 10.0 g of C(s), plus CO(g) and CO2(g), each at a partial pressure of 2.00 atm at 1,160 K.

(e)Predict whether the partial pressure of CO2(g) will increase, decrease, or remain the same as this system approaches equilibrium. Justify your prediction with a calculation

2 H2S(g)  2 H2(g) + S2(g)

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.

(b) Calculate the equilibrium concentration, in molL-1, of the following gases in the container at 483 K.

(i)H2(g)

(ii)H2S(g)

(d) Calculate the partial pressure of S2(g) in the container at equilibrium at 483 K.

(e) For the reaction H2(g) + S2(g)  H2S(g) at 483 K, calculate the value of the equilibrium constant, Kc.

C(s) + H2O(g)  CO(g) + H2(g)Hº = +131kJ

A rigid container holds a mixture of graphite pellets (C(s)), H2O(g), CO(g), and H2(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.

(a) Additional H2(g) is added to the equilibrium mixture at constant volume.

(b) The temperature of the equilibrium mixture is increased at constant volume.

(d) The graphite pellets are pulverized.

CO2(g) + H2(g)  H2O(g) + CO(g)

When H2(g) is mixed with CO2(g) at 2,000 K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured.

[H2]= 0.20 mol/L

[CO2]= 0.30 mol/L

[H2O] = [CO]= 0.55 mol/L

(a) What is the mole fraction of CO(g) in the equilibrium mixture?

(b) Using the equilibrium concentrations given above, calculate the value of Kc, the equilibrium constant for the reaction.

(d) When the system is cooled from 2,000 K to a lower temperature, 30.0 percent of the CO(g) is converted back to CO2(g). Calculate the value of Kc at this lower temperature.

(e) In a different experiment, 0.50 mole of H2(g) is mixed with 0.50 mole of CO2(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.

Precipitation Equilibrium

Section 1: Multiple Choice

1. How many moles of NaF must be dissolved in 1.00 liter of a saturated solution of PbF2 at 25 °C to reduce the [Pb2+] to 1 x 10¯6 molar? (Ksp of PbF2 at 25 °C = 4.0 x 10¯8)

(A) 0.020 mole
(B) 0.040 mole
(C) 0.10 mole
(D) 0.20 mole
(E) 0.40 mole

2. What is the net ionic equation for the reaction that occurs when aqueous copper(II) sulfate is added to excess 6-molar ammonia?

(A) Cu2+ + SO42¯ + 2 NH4+ + 2 OH¯ ---> (NH4)2SO4 + Cu(OH)2
(B) Cu2+ + 4 NH3 + 4 H2O --> Cu(OH)42¯ + 4 NH4+
(C) Cu2+ + 2 NH3 + 2 H2O --> Cu(OH)2 + 2 NH4+
(D) Cu2+ + 4 NH3 --> Cu(NH3)42+
(E) Cu2+ + 2 NH3 + H2O --> CuO + 2 NH4+

3. The solubility of CuI is 2 x 10¯6 molar. What is the solubility product constant, Ksp, for CuI?

(A) 1.4 x 10¯3
(B) 2 x 10¯6
(C) 4 x 10¯12
(D) 2 x 10¯12
(E) 8 x 10¯18

4. A white solid is observed to be insoluble in water, insoluble in excess ammonia solution, and soluble in dilute HCl. Which of the following compounds could the solid be?

(A) CaCO3
(B) BaSO4
(C) Pb(NO3)2
(D) AgCl
(E) Zn(OH)2

5. Equal volumes of 0.10-molar H3PO4 and 0.20-molar KOH are mixed. After equilibrium is established, the type of ion an solution in largest concentration, other than the K+ ion, is

(A) H2PO4¯
(B) HPO42¯
(C) PO43¯
(D) OH¯
(E) H3O+

6. Barium sulfate is LEAST soluble in a 0.01-molar solution of which of the following?

(A) Al2(SO4)3
(B) (NH4)2SO4
(C) Na2SO4
(D) NH3
(E) BaCl2

7. What is the molar solubility in water of Ag2CrO4? (The Ksp for Ag2CrO4 is 8 x 10¯12.)

(A) 8 x 10¯12 M
(B) 2 x 10¯12 M
(C) (4 x 10¯12 M)1/2
(D) (4 x 10¯12 M)1/3
(E) (2 x 10¯12 M)1/3

8. The net ionic equation for the reaction between silver carbonate and hydrochloric acid is

(A) Ag2CO3(s) + 2 H+ + 2 Cl¯ ---> 2 AgCl(s) + H2O + CO(g)
(B) 2 Ag+ + CO32¯ + 2 H+ + 2 Cl¯ ---> 2 AgCl(s) + H2O + CO2(g)
(C) CO32¯ + 2 H+ ---> H2O + CO2(g)
(D) Ag+ + Cl¯ ---> AgCl(s)
(E) Ag2CO3(s) + 2 H+ ---> 2Ag+ + H2CO3

9. A 20.0-milliliter sample of 0.200-molar K2CO3 solution is added to 30.0 milliliters of 0.400-molar Ba(NO3)2 solution. Barium carbonate precipitates. The concentration of barium ion, Ba2+, in solution after reaction is

(A) 0.150 M
(B) 0.160 M
(C) 0.200 M
(D) 0.240 M
(E) 0.267 M

10. A 1.0 sample of an aqueous solution contains 0.10 mol of NaCl and 0.10 mol of CaCl2. What is the minimum number of moles of AgNO3 that must be added to the solution in order to precipitate all of the Cl¯ as AgCl(s) ?

(A) 0.10 mol
(B) 0.20 mol
(C) 0.30 mol
(D) 0.40 mol
(E) 0.60 mol

Section 2: Free Response Questions

MgF2(s)  Mg2+(aq) + 2 F-(aq)

In a saturated solution of MgF2 at 18ºC, the concentration of Mg2+ is 1.21 x 10-3 molar. The equilibrium is represented by the equation above.

(a) Write the expression for the solubility-product constant, Ksp, and calculate its value at 18ºC.

(b) Calculate the equilibrium concentration of Mg2+ in 1.000 liter of saturated MgF2 solution at 18ºC to which 0.100 mole of solid KF has been added. The KF dissolves completely. Assume the volume change is negligible.

(c)Predict whether a precipitate of MgF2 will form when 100.0 milliliters of a 3.00 x 10-3-molar Mg(NO3)2 solution is mixed with 200.0 milliliters of a 2.00 x l0-3-molar NaF solution at 18ºC. Calculations to support your prediction must be shown.

(d)At 27ºC the concentration of Mg2+ in a saturated solution of MgF2 is 1.17 x 10-3 molar. Is the dissolving of MgF2 in water an endothermic or an exothermic process? Give an explanation to support your conclusion.

2. At 25ºC the solubility product constant, Ksp, for strontium sulfate, SrSO4, is 7.6×10-7. The solubility product constant for strontium fluoride, SrF2, is 7.9´10-10.

(a) What is the molar solubility of SrSO4 in pure water at 25ºC?

(b) What is the molar solubility of SrF2 in pure water at 25ºC?

(c) An aqueous solution of Sr(NO3)2 is added slowly to 1.0 litre of a well-stirred solution containing 0.020 mole F- and 0.10 mole SO42- at 25ºC. (You may assume that the added Sr(NO3)2 solution does not materially affect the total volume of the system.)

(i) Which salt precipitates first?

(ii) What is the concentration of strontium ion, Sr2+, in the solution when the first precipitate begins to form?

(c) As more Sr(NO3)2 is added to the mixture in (c) a second precipitate begins to form. At that stage, what percent of the anion of the first precipitate remains in solution?

3. Answer the following questions relating to the solubility of the chlorides of silver and lead.

(a) At 10C, 8.9  10-5 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C.

(iii) Calculate the value of the solubility-product constant, Ksp for AgCl(s) at 10C.

(b) At 25C, the value of Ksp for PbCl2(s) is 1.6  10-5 and the value of Ksp for AgCl(s) is 1.8  10-10.

(i)If 60.0 mL of 0.0400 M NaCl(aq) is added to 60.0 mL of 0.0300 M Pb(NO3)2(aq), will a precipitate form? Assume that volumes are additive. Show calculations to support your answer.

(ii) Calculate the equilibrium value of [Pb2+(aq)] in 1.00 L of saturated PbCl2 solution to which 0.250 mole of NaCl(s) has been added. Assume that no volume change occurs.

(iii) If 0.100 M NaCl(aq) is added slowly to a beaker containing both 0.120 M AgNO3(aq) and 0.150 M Pb(NO3)2(aq) at 25C, which will precipitate first, AgCl(s) or PbCl2(s)? Show calculations to support your answer.