Exam 1 Practice Problems
Chapter 11, 12 & 13
1. Explain what interactions must be present in order for a solution to form?
2. Define solvent and solute. What is the most common solvent?
3. Using the Solubility Curve located in the book or your notes, determine if the
following solutions are saturated, unsaturated, or supersaturated.
a. 25 g KNO3 in 200 g of water at 25 0C
b. 30 g of KClO3 in 100 g of water at 30 0C
c. 86 g of Pb(NO3)2 in 150 g of water at 55 0C
d. 45 g of KCl in 250 g of water at 5 0C
4. What factors affect the ability of a solute to dissolve in a solvent?
5. If 5.69 g of CO2 dissolves in 500.0 mL of water at 25.0 0C, what is the κH
(Henry’s Law constant) for CO2? The total pressure is total pressure of the
system is 2.5 atm and air pressure at 25 0C is 0.895 atm.
6. Determine the solubility of N2 in water exposed to air at 25 0C if the
atmospheric pressure is 1.5 atm. Assume that the mole fraction of nitrogen is
0.78 in air and the Henry’s law constant for nitrogen in water a this
temperature is 6.1 X 10-4 M/atm.
7. Determine ΔHsolute for KBr if the ΔHsolution(KBr) = +19.9 kJ/mol and the
ΔHhydration(KBr) = -670 kJ/mol.
8. Calculate the molality of a solution formed by dissolving 25.6 g of KNO3 in
550 mL of water.
9. What is the molarity of a solution that has 26.8 g Na2SO4 dissolved to a total
volume of 2.5 L.
10. An aqueous KNO3 solution is made using 72.3 g of KNO3 diluted to a total
solution volume of 1.50 L. Calculate the mass percent of the solution. Assume
a density of 1.05 g/mL for the solution.)
11. A hard water sample contains 0.0085 % Ca by mass (in the form of Ca2+
ions). How much water (in grams) contains 1.2 g of Ca?
12. Assume a solution containing 56.8 g of ethylene glycol in 250.0 g of water is
ideal. What is the vapor pressure of water over the solution at 30.0 0C?
(vapor pressure of pure H2O is 31.8 mm Hg; MW ethylene glycol is 62.10
g/mol)
13. Determine the mass percent of Na2SO4 given the following information.
The vapor pressure of Na2SO4 is 68.4 mm Hg at 50.0 0C.
The vapor pressure of pure water at this temperature is 92.6 mm Hg
Assume you have 1 mol of water
14. What mass of NaCl is contained in 24.88 g of 15.00 % by mass solution of
NaCl in water?
15. Calculate the freezing point of a solution of 556.0 g of ethylene glycol
(C2H6O2) dissolved in 500.0 g of water. Kf=1.86 0C/m.
16. The boiling point elevation of an aqueous sucrose solution is found to be 0.59
0C. What mass of surcrose (MW = 342.30 g/mol) would be needed to
dissolved in 500.0 g of water? Kb = 0.512 0C/m.
17. If 95.6 g of ethylene glycol is dissolved in 250.0 grams of water, what is the
boiling point and freezing point of the solution? (kb = 0.512 0C/m; kf = 1.86
0C/m)
18. Predict the sign of ΔS for each process:
a. H2O (g)  H2O (l)
b. Solid carbon dioxide sublimes
c. 2N2O (g)  2N2 (g) + O2(g)
d. boiling of water
e. I2(g)  I2 (s)
f. CaCO3(s)  CaO(s) + CO2 (g)
19. Consider the combustion of propane gas:
C3H8 (g) + 5 O2  3 CO2 (g) + 4H2O (g)
ΔH = -2044 kJ
a. Calculate the entropy change in the surroundings at 25 OC.
b. Determine the sign of the entropy change for the system.
c. Determine the sign of the entropy change for the universe. Will the
reaction be spontaneous?
20. Consider the reaction between nitrogen and oxygen gas to form dinitrogen
monoxide:
2N2 + O2 (g)  2N2O (g)
ΔHrxn = +163.2 kJ
a. Calculate the entropy change in the surroundings at 25 OC.
b. Determine the sign of the entropy change for the system.
c. Determine the sign of the entropy change for the universe. Will the
reaction be spontaneous?
21. Consider the reaction for the decomposition of carbon tetrachloride gas:
CCl4 (g)  C(s, graphite) + 2Cl2 (g)
ΔH = +95.7 kJ; ΔS = +142.2 J/K
a. Calculate ΔG at 25 OC and determine whether the reaction is
spontaneous.
b. If the reaction is not spontaneous at 25 OC, determine at what
temperature (if any) the reaction becomes spontaneous.
22. Consider the following reaction:
C2H4 (g) + H2 (g)  C2H6 (g)
ΔΗ = -137.5 kJ; ΔS = -120.5 J/K
Calculate ΔG at 25 OC and determine whether the reaction is spontaneous.
Does ΔG become more negative or more positive as the temperature
increases?
23. Calculate ΔSOrxn for the balanced chemical equation:
4 NH3 (g) + 5O2 (g)  4 NO (g) + 6H2O (g)
24. One of the possible initial steps in the formation of acid rain is the oxidation
of the pollutant SO2 and SO3 by the reaction:
SO2 (g) + ½ O2 (g)  SO3 (g)
Calculate ΔGOrxn at 25 OC and determine whether the reaction is spontaneous.
25. Consider the oxidation of NO to NO2:
NO (g) + ½ O2(g)  NO2 (g)
Calculate ΔGOrxn at 25 OC and determine whether the reaction is spontaneous.
26. Use the standard free energies of formation to determine the ΔGOrxn for this
reaction at 25 OC.
CH4 (g) + 8 O2(g)  CO2 (g) + 2 H2O (g) + 4 O3 (g)
27. Use the standard free energies of formation to determine the ΔGOrxn for this
reaction at 25 OC.
2CO (g) + 2NO (g)  2 CO2 (g) + N2 (g)
28. Find ΔGOrxn for the reaction:
3C (s) + 4 H2 (g)  C3H8 (g)
Use the following reactions with known ΔG values:
C3H8 (g) + 5O2 (g)  3CO2 (g) + 4 H2O (g)
ΔGOrxn = -2074 kJ
C (s) + O2 (g)  CO2 (g)
ΔGOrxn = -394.4 kJ
2H2 (g) + O2 (g)  2H2O (g)
ΔGOrxn = -457.1 kJ
29. The following reaction is carried out at 298 K:
2NO (g) + O2 (g)  2 NO2 (g)
ΔGOrxn = -71.2 kJ
Calculate ΔGrxn under the conditions:
PNO = 0.100 atm; PO2 = 0.100 atm; PNO2 = 2.00 atm
30. Consider the following reaction at 298 K:
2H2S (g) + SO2 (g)  3 S (s) + 2H2O (g)
ΔGOrxn = -102. kJ
Calculate ΔGrxn under the conditions:
[H2O] = 0.250 M; [SO2] = 0.365 M; [H2S] = 0.485 M
31. Using Gibbs free energies of formation calculate the equilibrium constant for
the following reaction at 298 K.
N2O4 (g) ⇌ 2 NO2 (g)
32. Calculate ΔGOrxn at 298 K for the following reaction:
I2 (g) + Cl2 (g) ⇌ 2ICl
Kp = 81.9
33. Calculate the entropy change of the surroundings at 25 OC for the reaction
below:
SO2 (g) + ½ O2  SO3 (g)
ΔHrxn = -98.9 kJ
34. The reaction 4NH3 (g) + 5O2 (g)  4 NO (g) + 6 H2O (g) has a ΔH = +102.5 kJ
and a ΔS = 178.8 J/K at 298 K. Calculate ΔG and determine if it is
spontaneous.
35. The reaction CCl4 (g)  C (s, graphite) + 2Cl2 (g) has ΔH = +86.5 kJ and ΔS =
+157.6 J/K. Calculate the minimum temperature it will be spontaneous.
36. Calculate the ΔSO for the reaction:
CCl4 (g)  C (s, graphite) + 2Cl2 (g)
37. Which substance would you expect to have the higher standard molar
entropy (SO) in each pair at 25 OC?
a.
b.
c.
d.
CO(g): CO2 (g)
CH3OH (l) : CH3OH (g)
Ar(g); CO2 (g)
CH4 (g); SiH4 (g)
38. Calculate the free energy change for the reaction at 25 OC. Is the reaction
spontaneous?
2 Ca (s ) + O2 (g)  2CaO (s)
ΔHOrxn = -1269.8 kJ; ΔSOrxn = -364.6 J/K
39. A reaction has a positive ΔH and a negative ΔS. Under what conditions will
the reaction be spontaneous?
40. Express the equilibrium constant for the chemical equation
CH3OH (g) ⇌ CO(g) + 2H2 (g)
41. Express the equilibrium constant for the chemical equation
C3H8 (g) + 5O2 (g) ⇌ 3CO2 (g) + 2H2 (g)
42. Write the equilibrium constant expression, K, and predict the position of
equilibrium for the reaction:
H2 (g) + Br2 (g) ⇌ 2HBr (g)
K=1.9X1019
43. The reaction A (g) ⇌ 2B (g) has an equilibrium constant of K = 0.010. What is
the equilibrium constant for the reaction B (g) ⇌ ½ A (g)?
44. Consider the chemical equation and equilibrium constant for the synthesis of
ammonia at 25 OC:
N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
K = 3.7 X 108
Calculate the equilibrium constant for the following reaction at 25 OC:
NH3(g) ⇌ ½ N2 (g) + 3/2 H2 (g)
K’ = ??
45. Nitrogen monoxide, a pollutant in automobile exhaust, is oxidized to nitrogen
oxide in the atmosphere according to the equation:
2 NO (g) + O2 (g) ⇌ 2NO2 (g)
Find Kc for this reaction.
Kp = 2.2X1012 at 25 OC
46. Consider the following reaction and corresponding value of Kc:
H2 (g) + I2 (g) ⇌ 2HI (g)
What is the value of Kp at this temperature?
Kc = 6.2 X 102 at 25 OC
47. What is the equilibrium constant for the following reaction:
2CO (g) ⇌ CO2 (g) + C (s)
48. What is the equilibrium constant for the following reaction:
CO2 (g) + H2O (l) ⇌ H+ (aq) + HCO3- (aq)
49. What is the value for the equilibrium constant for the following reaction:
4HCl (g) + O2 (g) ⇌ 2H2O (l) + 2Cl2 (g)
Given the equilibrium concentrations: [HCl] = 0.26 M; [O2] = 0.32 M; [H2O] = 0.65
M; [Cl2] = 0.59 M
50. What is the value for the equilibrium constant for the following reaction:
CaCO3 (s) ⇌ CaO (s) + CO2 (g)
Given at equilibrium 2.5 g CaCO3; 1.35 g CaO; 3.45 g CO2 in a 1.5 L container.
51. What is the value for Kp in question #52 at 25 OC ?
52. Consider the following reaction:
CO(g) + 2H2(g) ⇌ CH3OH (g)
A reaction mixture at 78 OC initially contains [CO] = 0.500 M and [H2] = 1.25
M. At equilibrium, the CO concentration is found to be 0.15 M. What is the
value of the equilibrium constant?
53. Consider the following reaction:
2 CH4 (g) ⇌ C2H2 (g) + 3H2 (g)
A reaction mixture at 78 OC initially contains [CH4] = 0.500 M. At equilibrium,
the C2H2 concentration is found to be 0.105 M. What is the value of the
equilibrium constant?
54. Consider the reaction and its equilibrium constant:
I2 (g) + Cl2 (g) ⇌ 2ICl (g)
Kp=81.9
A reaction mixture contains PI2 = 0.587 atm; PCl2 0.894 atm; PICl = 0.953 atm.
Which direction will the reaction proceed?
55. A reaction mixture contains NO2 and N2O4 at 0.0255 M and 0.0331 M ,
respectively. Which direction will the reaction proceed?
N2O4 ⇌ 2NO2
-3
Kc = 5.85 X 10
56. Consider the reaction:
2COF2 (g) ⇌ CO2 (g) + CF4 (g)
Kc = 2.00 at 1000 OC
In an equilibrium mixture, the concentration of COF2 is 0.255 M and the
concentration of CF4 is 0.188 M. What is the equilibrium concentration of CO2?
57. Molecular iodine (I2) decomposes at high temperature to form I atoms
according to the reaction:
I2 (g) ⇌ 2I (g)
Kc= 0.011 at 1200 OC
In an equilibrium mixture, the concentration of I2 is 0.10 M. What is the
equilibrium concentration of I?
58. Consider the following reaction:
N2 (g) + O2 (g)⇌ 2NO (g)
Kc = 3.5 X 10-5 (at 150 OC)
A reaction mixture initially contains [N2] = 0.250 M and [O2] = 0.350 M. Find
the equilibrium concentrations of the reactants and products.
59. Consider the following reaction at equilibrium. What effect will decreasing
the temperature have on the system?
I2 (g) ⇌ 2I (g)
ΔH = -359 kJ (at 298 K)
60. Consider the following reaction at equilibrium. What effect will decreasing
the pressure have on the system?
Fe3O4 (s) + CO (g) ⇌ 3FeO (s) + CO2 (g)
Kc = 6.26 X 10-19 (at 298 K)