HOMEWORK 3A
1. In each of the following pairs, tell which has the higher entropy.
(a) One mole of liquid water or one mole of water vapor
(b) One mole of dry ice or one mole of carbon dioxide at 1 atm pressure
(c) One mole of diamond or one mole of graphite
(d) One mole of methane or one mole of ethane
2. Will the entropy change of each of the following processes be positive or negative, and will the
disorder in each process increase or decrease?
(a) One mole of solid methanol subliming to one mole of gaseous methanol.
(b) One mole of liquid methanol freezing to one mole of solid methanol.
(c) One mole of sugar crystals and five moles of water mixing to form a solution.
(d) One mole of gaseous carbon dioxide and five moles of water mixing to form carbonated water.
3. Predict the sign of the entropy change in each of the following reactions.
(a) XeO4 (s)  Xe (g) + 2O2 (g)
(b) 2Na (s) + ½O2 (g)  Na2O (s)
(c) 2CO (g) + O2 (g)  2CO2 (g)
(d) Ba2+ (aq) + SO42- (aq)  BaSO4 (s)
(e) 2H+ (aq) + S2- (aq)  H2S (g)
(f) Cl2 (g) + F2 (g)  2ClF (g)
4. Using the data from Handout 5, what is the standard enthalpy of formation of BaO (s)? What does this
mean?
5. Using the data from Handout 5, what is the standard absolute entropy of BaO (s)? What does this
mean?
6. Using data from the Handout 5, calculate the standard change in entropy, ΔSº, for the following
reactions.
(a) S (s, rhombic) + O2 (g)  SO2 (g)
(b) C2H5OH(l) + 3O2(g)  2CO2(g) + 3H2O(g)
HOMEWORK 3B
1. For the vaporization of methanol at 25ºC:
CH3OH (l)  CH3OH (g)
(a) Using data from the Handout 5, calculate the standard change in enthalpy for the phase change
(the heat of vaporization)
(b) Using data from the Handout 5, calculate the standard change in entropy for the phase change (the
entropy change of the system)
(c) Calculate the standard change in entropy of the surroundings for the phase change
(d) Calculate the standard change in entropy of the universe for the phase change
(e) Is the forward or reverse phase change spontaneous at 25ºC?
2. Predict whether each of the following processes will be spontaneous, nonspontaneous, or it cannot be
determined.
(a) A exothermic process in which the entropy increases
(b) A exothermic process in which the entropy decreases
(c) A endothermic process in which the entropy increases
(d) A endothermic process in which the entropy decreases
3. Using the data from Handout 5, what is the standard free energy of formation of BaO (s)? What does
this mean?
4. For the reaction at 25ºC
2Ag (s) + Hg2Cl2 (s)  2AgCl (s) + 2Hg (l)
use data from Handout 5 to answer the following.
(a) Calculate ΔHº
(b) Calculate ΔSº
(c) Calculate ΔGº
(d) Calculate ΔGº from ΔGº = ΔHº - T ΔSº
(e) Is the reaction spontaneous under standard conditions?
(f) Do the enthalpy change and the entropy change work for or against spontaneity?
(g) Which factor predominates?
5. For the phase change:
Br2 (l)  Br2 (g)
(a) Using data from the appendix, calculate the standard change in enthalpy for the phase change (the
heat of vaporization)
(b) Using data from the appendix, calculate the standard change in entropy for the phase change
(c) Calculate the standard free energy change, ΔGº, for the reaction at 20.ºC, and tell if the forward or
reverse reaction is spontaneous at this temperature
(d) Calculate the standard free energy change, ΔGº, for the reaction at 80.ºC, and tell if the forward or
reverse reaction is spontaneous at this temperature
(e) Calculate the boiling point of liquid bromine
HOMEWORK 3C
1. For the reaction:
2H2S (g) + SO2 (g) ⇆ 3S (s, rhombic) + 2H2O (g)
if the actual pressures of each of these gases are pH2S = 1.0 x 10-4 atm, pSO2 = 1.0 x 10-2 atm, and pH2O =
3.0 x 10-2 atm, calculate ΔG at 298 K.
2. For the reaction
Cl2 (g) + I2 (s) ⇆ 2ICl (g)
Given that ΔGfº = -5.5 kJ/mol for ICl (g), answer the following.
(a) Calculate ΔGº for the forward reaction
(b) Is the forward reaction spontaneous under standard conditions?
(c) Calculate Keq at 298 K
3. For the combustion of liquid methanol:
CH3OH (l) + 1½O2 (g) ⇆ CO2 (g) + 2H2O (l)
(a) Calculate ΔGº
(b) Is the reaction spontaneous under standard conditions?
(c) Calculate Keq at 298 K
(d) Does the Keq favor reactants or products?
(e) What effect would an increase in temperature have on the spontaneity of the reaction ?
(f) What effect would an increase in pressure have on the spontaneity of the reaction?
4. Acetic acid ionizes according to the following equation:
HC2H3O2 (aq) ⇆ H+ (aq) + C2H3O2- (aq)
At 298 K the ΔG°f for acetic acid is -399 kJ/mol, and the ΔG°f for the acetate ion is -372 kJ/mol.
(a) Calculate the standard free energy change of the reaction.
(b) From the standard free energy change of the reaction, calculate the Ka of acetic acid at 298 K.
(c) How does your calculated Ka compare with the value found in Table 14.2?
5. Metacresol (which will be represented by HCre) is a weak organic acid with Ka = 1.0 x 10-10.
(a) Write the equilibrium constant expression for the ionization of metacresol in water.
(b) What is concentration of the Cre- ion in a 1.00 M solution of metacresol in water?
(c) What is the pH of the solution?
(d) What is the standard free energy change of the ionization of metacresol in water?
6. The solubility of potassium chloride in water is 347 g/L at 20.ºC, and 802 g/L at 100.ºC.
(a) Calculate the Ksp for potassium chloride at each temperature.
(b) Determine the heat of solution and the entropy change of solution of potassium chloride by using
a van’t Hoff plot.
HOMEWORK 3D
1. Assuming the concentrations of 1 M for all of the following solutions, use standard reduction
potentials found in Table 18.1 to determine which of the following reactions are spontaneous.
(a) Zn (s) + Mg2+ (aq) → Zn2+ (aq) + Mg (s)
(b) Fe (s) + Cl2 (g) → Fe2+ (aq) + 2Cl- (aq)
(c) 4Ag (s) + O2 (g) + 4H+ (aq) → 4Ag+ (aq) + 2H2O (l)
(d) 2AgCl (s) → 2Ag (s) + Cl2 (g)
2. Consider the cell
Ag (s) | Ag+ (1.0 M) || Cu2+ (1.0 M) | Cu (s)
(a) Write the spontaneous chemical reaction that takes place in this cell
(b) What is Ɛº for the cell?
(c) Which metal, Ag or Cu, will be the anode, and which metal will be the cathode?
(d) Do the electrons flow from Ag to Cu in the external circuit, or the other way?
3. Consider the cell
Au (s) | Au3+ (1.0 M) || Mg2+ (1.0 M) | Mg (s)
(a) Determine the spontaneous chemical reaction that takes place in this cell, assuming that the line
notation may be written incorrectly
(b) What is Ɛº for the cell?
(c) Which metal, Au or Mg, will be the anode, and which metal will be the cathode?
(d) Do the electrons flow from Au to Mg in the external circuit, or the other way?
4. Find the missing standard reduction potentials for these following half reactions from Table 18.1:
MnO4- (aq) + 8H+ (aq)
Au3+ (aq)
Cl2 (g)
AuCl4- (aq)
4H+ (aq) + NO3- (aq)
+
+
+
+
+
5e- →
3e- →
2e- →
3e- →
3e- →
Mn2+ (aq) + 4H2O (l)
Au (s)
2Cl- (aq)
Au (s) + 4Cl- (aq)
NO (g) + 2H2O (l)
Ɛ° = +1.51 V
Ɛ° = +1.50 V
Ɛ° =
Ɛ° =
Ɛ° =
Assuming all reactants and products are at unit activity,
(a) What substance from above is the best oxidizing agent and what is the best reducing agent?
(b) Will permanganate oxidize metallic gold?
(c) Will metallic gold reduce nitric acid?
(d) Will nitric acid oxidize metallic gold in the presence of chloride ions?
(e) Will metallic gold reduce pure chlorine gas in the presence of water?
(f) Will chlorine oxidize metallic gold if chloride ions are present?
(g) Will permanganate oxidize chloride ions?
HOMEWORK 3E
1. Concerning half-cell reactions, outline the conditions under which the potentials will be additive, and
when they will not.
2. Consider the cell
Ni (s) | Ni2+ (0.010 M) || Sn2+ (1.0 M) | Sn (s)
(a) Write the spontaneous chemical reaction that takes place in this cell.
(b) Which metal, Ni or Sn, will be the anode, and which metal will be the cathode?
(c) What is Ɛº for the cell?
(d) What is Ɛ for the cell at 25°C with the concentrations specified above?
3. A copper-zinc battery is set up under standard conditions with all species at unit activity. Initially, the
voltage developed by this cell is 1.10 V. As the battery is used, the concentration of the copper (II) ion
gradually decreases, and that of the zinc ion increases.
(a) According to LeChatelier’s Principle, should the voltage of the cell increase or decrease?
(b) Calculate the ratio of activities of products to reactants, Q, when the cell voltage is 1.00 V at 25°C
4. Consider the cell
Zn (s) | Zn2+ (0.0010 M) || Cu2+ (0.0010 M) | Cu (s)
for which Ɛº = 1.10 V. Does the cell voltage increase, decrease, or remain the same when each of the
following changes is made?
(a) Excess 1.0 M ammonia is added is added to the cathode compartment.
(b) H2S gas is bubbled into the anode compartment.
5. Find the standard reduction potentials for these following half reactions from Handout 6:
Hg22+ (aq) + 2e- → 2Hg (l)
Cu2+ (aq) + 2e- → Cu (s)
Ɛ° =
Ɛ° =
Assuming all reactants and products are at unit activity,
(a) Write the balanced overall reaction for a successful cell made from these two couples.
(b) Write the line notation for the cell.
(c) What is Ɛº for the cell?
(d) What is the equilibrium constant for the reaction?
(e) Calculate the voltage of the cell when [Hg22+] = 0.10 M and [Cu2+] = 0.010 M.
6. A standard hydrogen half-cell is coupled to a standard silver half-cell. Sodium bromide is added to the
silver half-cell, causing precipitation of AgBr, until a concentration of 1.00 M Br- is reached. The
voltage of the cell at this point is 0.072 V.
(a) What is Ɛº for the hydrogen-silver cell?
(b) What is the concentration of the silver ions in the cell when the voltage is 0.072 V?
(c) What is the Ksp for silver bromide?
HOMEWORK 3F
1. Give the electrolysis products at the anode and cathode for each of the following liquids or solutions.
(a) H2O (l)
(b) LiBr (l)
(c) LiBr (aq)
(d) CuBr2 (aq)
(a) Cu(BrO3)2 (aq)
(b) NaBrO3 (aq)
(c) HBr (aq)
(h) HBrO3 (aq)
2. How many grams of metallic aluminum can be obtained by passing a current of 1.00 A through
molten aluminum chloride for 7.00 hours?
3. The quantity of charge passed through a circuit is sometimes measured by determining the mass of
solid silver deposited by the electrolysis of a silver ion solution. If a cathode increases in mass by
0.197 g, how coulombs have passed through the electrolysis cell?
4. Molten zinc chloride is electrolyzed by passing a current of 3.0 A through an electrolysis cell for a
certain length of time. In this process 24.5 g of zinc are deposited on the cathode.
(a) What is the half-reaction that occurs at the cathode?
(b) What is the half-reaction that occurs at the anode?
(c) How long does the process take?
(d) What mass of chlorine gas is liberated at the anode?
HOMEWORK 3R
1. In each of the following pairs, tell which has the higher entropy.
(a) One mole of liquid water or one mole of water vapor
(b) One mole of solid sugar or one mole of dissolved sugar
(c) One mole of fluorine gas or one mole of chlorine gas
(d) One mole of oxygen gas or one mole of dissolved oxygen
2. Predict the sign of the entropy change in each of the following reactions.
(a) NH4Cl (g)  NH3 (g) + HCl (g)
(b) P4 (s) + 6H2 (g)  4PH3 (g)
(c) 2C2H6 (g) + 7O2 (g)  4CO2 (g) + 6H2O (g)
(d) N2 (g) + O2 (g)  2NO (g)
(continued on next page)
3. For the vaporization of dinitrogen tetroxide at 25ºC:
N2O4 (l)  N2O4 (g)
(a) Using data from the Handout 5, calculate the standard change in enthalpy for the phase change
(the heat of vaporization)
(b) Using data from the Handout 5, calculate the standard change in entropy for the phase change (the
entropy change of the system)
(c) Calculate the standard change in entropy of the surroundings for the phase change, and assume
the answer is significant to three digits
(d) Calculate the standard change in entropy of the universe for the phase change
(e) Is the forward or reverse phase change spontaneous at 25ºC?
(f) Calculate the normal boiling point of nititrogen tetroxide.
4. Tell what each of the following indicates about a process.
(a) ΔH > 0
(b) ΔH < 0
(c) ΔS > 0
(d) ΔS < 0
(e) ΔG > 0
(b) ΔG < 0
(c) ΔG = 0
(d) ΔGº = 0
5. For the reaction
6CO2 (g) + 6H2O (l)  C6H12O6 (s) + 6O2 (g)
use data from the Handout 5 to answer the following.
(a) Calculate ΔHº
(b) Calculate ΔSº
(c) Calculate ΔGº
(d) Does the ΔHº for this reaction favor spontaneity?
(e) Does the ΔSº for this reaction favor spontaneity?
(f) Would an increase in temperature favor spontaneity?
6. For the combustion of sucrose:
C12H22O11 (s) + 12O2 (g)  12CO2 (g) + 11H2O (l)
the ΔHº = -3,840 kJ/mol and the ΔSº = 551 J/molK .
(a) Does the ΔHº for this reaction favor spontaneity?
(b) Does the ΔSº for this reaction favor spontaneity?
(c) Would an increase in temperature favor spontaneity?
(d) Use data from the Handout 5 to calculate the absolute standard entropy, Sº, of sucrose.
(continued on next page)
7. For one of the reactions that destroys ozone in the upper atmosphere:
NO (g) + O3 (g) ⇆ NO2 (g) + O2 (g)
(a) Calculate ΔGº
(b) Is the reaction spontaneous under standard conditions?
(b) Write the Keq expression for the reaction in terms of activities
(d) Calculate Keq at 298 K
(e) Does the Keq favor reactants or products?
(f) If the actual pressures of each of these gases in the upper atmosphere are pNO = 1.00 x 10-6 atm,
pO3 = 2.00 x 10-6 atm, pNO2 = 1.00 x 10-7 atm, and pO2 = 1.00 x 10-3 atm, calculate ΔG for the
reaction at 298 K.
(g) Is the reaction spontaneous under these conditions?
8. Using only the data given below for following reaction at 298 K:
Cl2 (g) + 3F2 (g) → 2ClF3 (g)
ClF3 (g)
ΔGºf (kJ/mol)
ΔHºf (kJ/mol)
-123
-163
Sº (J/molK)
281
(a) Calculate the standard free energy change for the reaction at 298 K.
(b) Calculate the equilibrium constant for the reaction at 298 K.
(c) Calculate the standard enthalpy change for the reaction at 298 K.
(d) Calculate the standard entropy change for the reaction at 298 K.
(e) If ClF3 were produced as a liquid rather than a gas, how would the sign and magnitude of ΔSº for
the reaction be affected?
9. At 298 K, the pH of a 0.10 M HX solution is 3.35.
(a) Calculate the acid ionization constant for HX at 298 K.
(b) Calculate the standard free energy change for the ionization of HX at 298 K.
10. For the following reaction:
2NO2 (g) ⇆ N2O4 (g)
the ΔHº and ΔSº are -58.03 kJ and -176.6 J/K, respectively.
(a) Calculate Keq for the above reaction at 298 K.
(b) Assuming that ΔHº and ΔSº are temperature independent, calculate Keq for the above reaction at
373 K.
11. The solubility of magnesium chloride in water is 543 g/L at 20.ºC, and 726 g/L at 100.ºC.
(a) Calculate the Ksp for magnesium chloride at each temperature.
(b) Determine the heat of solution and the entropy change of solution of potassium chloride by using
a van’t Hoff plot.
(continued on next page)
12. Assuming the concentrations of 1 M for all of the following solutions, use standard reduction
potenetials found on Handout 6 to determine which of the following reactions are spontaneous.
(a) Cr (s) + Al3+ (aq) → Cr3+ (aq) + Al (s)
(b) Ba (s) + Zn2+ (aq) → Ba2+ (aq) + Zn (s)
(c) Pb (s) + PbO2 (s) + 4H+ (aq) → 2Pb2+ (aq) + 2H2O (l)
13. Use the standard reduction potentials for these following half reactions from Handout 6:
Zn2+ (aq)
Br2 (l)
La3+ (aq)
Fe3+ (aq)
+ 2e- → Zn (s)
+ 2e- → 2Br- (aq)
+ 3e- → La (s)
+ e- → Fe2+ (aq)
Assuming all reactants and products are at unit activity,
(a) What substance from above is the best oxidizing agent and what is the best reducing agent?
(b) Will bromine oxidize metallic zinc?
(c) Will iron (II) ions reduce lanthanum (III) ions?
(d) Will zinc ions oxidize iron (II) ions?
14. Consider the cell
Fe (s) | Fe2+ (1.0 M) || Ag+ (1.0 M) | Ag (s)
(a) Write the spontaneous chemical reaction that takes place in this cell
(b) Which metal, Fe or Ag, will be the cathode, and which metal will be the anode?
(c) What is Eº for the cell?
(d) Do the electrons flow from Fe to Ag in the external circuit, or the other way?
(e) What is the equilibrium constant for the reaction at 298 K?
(f) Calculate Q when the cell voltage is 1.00 V at 298 K.
(g) Calculate the voltage of the cell when [Fe2+] = 0.10 M and [Ag+] = 0.010 M at 298 K.
15. Find the standard reduction potentials for these following half reactions from Handout 6:
Cr3+ (aq) + 3e- → Cr (s)
Cu+ (aq) + e- → Cu (s)
Assuming all reactants and products are at unit activity,
(a) Write the balanced overall reaction for a successful cell made from these two couples.
(b) Write the line notation for the cell.
(c) What is Ɛ º for the cell?
(d) What is the equilibrium constant for the reaction at 298 K?
(e) Calculate E for the cell when [Cr3+] = 0.10 M and [Cu+] = 0.010 M at 298 K.
(continued on next page)
16. Give the electrolysis products at the anode and cathode for each of the following liquids or solutions.
(a) CuF2 (l)
(b) CuF2 (aq)
(c) KF (aq)
(d) KNO3 (aq)
17. Write the anode half-reactions and the cathode half-reaction for the electrolysis of each of the
following:
(a) AuI3 (aq)
(b) H2O (l)
18. How many grams of metallic silver can be obtained by passing a current of 2.50 A through aqueous
silver nitrate for 3.00 minutes?
19. What current would be necessary to plate out 0.150 grams of tin metal from a tin (II) solution in a time
period of 2.00 minutes?
20. How long must a current of 1.5 A be passed through an aqueous solution of platinum (IV) ions to
plate out 1.00 g of platinum metal?
HOMEWORK 3R ANSWERS
1. (a) vapor
(b) dissolved
(c) chlorine
(d) gas
2. (a) positive
(b) negative
(c) positive
(d) positive
3. (a) ΔHºvap = 30. kJ
(b) ΔSºvap = 95 J/K
(c) ΔSºsurr = -101 J/K
(d) ΔSºuniv = -6 J/K
(b) exothermic
(c) increased disorder
(d) increased order
(f) spontaneous
(g) equilibrium
(f) 320 K (2 sig fig’s)
(e) no
4. (a) endothermic
(e) nonspontaneous
(h) equilibirium when all substances are at standard states
5. (a) ΔHº = 2802 kJ
(b) ΔSº = -262 J/K
(e) no
(d) no
(b) yes
(c) yes
(d) 327 J/molK
(b) yes
(c) Keq = aNO2aO2/aNOaO3
(e) products
(f) -188 kJ
(g) yes
(b) 1.32 x 1043
(c) -326 kJ
(d) -270 J/K
(f) no
6. (a) yes
7. (a) ΔGº = -198 kJ
34
(d) Keq = 5.10 x 10
8. (a) -246 kJ
(c) ΔGº = 2875 kJ
(e) larger negative number
9. (a) Ka = 2.0 x 10-6
(b) ΔGº = 33,000 J
10. (a) 8.9
(b) 0.080
11. (a) 742, 1770
(b) 9910 J, 88.7 J/K
(continued on next page)
12. (a) nonspontaneous
(b) spontaneous
13. (a) Br2 oxidizing agent, La reducing agent
(a) no
(c) spontaneous
(b) yes
(d) no
14. (a) Fe + 2Ag+ → Fe2+ + 2Ag
(c) 1.24 V
(b) Fe anode, Ag cathode
(d) Fe to Ag
41
(e) 8.79 x 10
(f) 1.31 x 108
(g) 1.15 V
15. (a) Cr + 3Cu+ → Cr3+ + 3Cu
(c) 1.25 V
(b) Cr(s) | Cr3+ (aq) || Cu+ (aq) | Cu (s)
(d) 2.65 x 1063
(e) 1.15 V
16. (a) anode – F2 (g), cathode – Cu (s)
(b) anode – F2 (g), cathode – Cu (s)
(c) anode – F2 (g), cathode – H2 (g)
(d) anode – O2 (g), cathode – H2 (g)
17. (a) anode – 2I- → I2 + 2e(b) anode – 2H2O → O2 + 4H+ + 4e18. 0.503 g
19. 2.03 A
20. 22 minutes
cathode – Au3+ + 3e- → Au
cathode – 4H2O + 4e- → 2H2 + 4OH-