EXTRA HOMEWORK 3A
1. In each of the following pairs, tell which has the higher entropy.
(a) One mole of ice or one mole of liquid water
(b) One mole of liquid propane or one mole of gaseous propane
(c) One mole of gray tin (diamond-like structure) or one mole of white tin (metal-like structure)
(d) One mole of solid magnesium nitrate or one mole of aqueous magnesium nitrate
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 aluminum melting to one mole of molten aluminum.
(b) One mole of iodine vapor deposing to one mole of solid iodine
(c) One mole of dissolved sodium acetate crystallizing out of an aqueous solution
(d) One mole of dissolved carbon dioxide bubbling out of a soda
3. Predict the sign of the entropy change in each of the following reactions.
(a) BaCO3 (s) → BaO (s) + CO2 (g)
(b) Mg (s) + Cl2 (g) → MgCl2 (s)
(c) CH4 (g) + 2O2 (g) → 2CO2 (g) + 2H2O (l)
(d) Ni3(PO4)2 (s) → 3Ni2+ (aq) + 2PO43- (aq)
(e) 2H+ (aq) + SO32- (aq)  H2O (l) + SO2 (g)
(f) Br2 (l) + Cl2 (g) → 2BrCl (l)
4. Using the data from Handout 5, what is the standard enthalpy of formation of N2O (g)? What does this
mean?
5. Using the data from Handout 5, what is the standard absolute entropy of N2O (g)? What does this
mean?
6. Using data from the appendix, calculate the standard change in entropy, ΔSº, for the following
reactions.
(a) 2S (s, monoclinic) + 3O2 (g) → 2SO3 (g)
(b) C3H8 (g) + 5O2 (g)  3CO2 (g) + 4H2O (g)
*7. 8 molecules are placed in a two-bulbed container. Calculate the positional probability of finding all 8
molecules in the left bulb.
EXTRA HOMEWORK 3B
1. For the allotropic phase change of phosphorus at 25ºC:
P (s) (white)  P (s) (red)
(a) Using data from the appendix, calculate the standard change in enthalpy for the allotropic phase
change
(b) Using data from the appendix, calculate the standard change in entropy for the allotropic phase
change
(c) Calculate the standard change in entropy of the surroundings for the allotropic phase change
(d) Calculate the standard change in entropy of the universe for the allotropic phase change
(e) Is the forward or reverse allotropic phase change spontaneous at 25ºC?
2. Predict whether each of the following processes will be spontaneous, nonspontaneous, or it cannot be
determined.
(a) ∆H = + and ∆S = +
(b) ∆H = + and ∆S = –
(c) ∆H = – and ∆S = +
(d) ∆H = – and ∆S = –
3. Using the data from Handout 5, what is the standard free energy of formation of N2O (g)? What does
this mean?
4. For the reaction at 25ºC
Fe2O3 (s) + 3H2 (g)  2Fe (s) + 3H2O (g)
use data from the appendix 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) At a temperature higher than 25ºC, would the forward reaction be more or less spontaneous?
5. For the phase change:
C6H6 (l)  C6H6 (g)
∆Hº = 33.9 kJ and ∆Sº = 96.4 J/K.
(a) 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
(b) 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
(c) Calculate the boiling point of liquid benzene
(continued on next page)
*6. The combustion reaction for butyric acid is:
C3H7CO2H (l) + 5O2 (g) → 4H2O (l) + 4CO2 (g)
The standard enthalpy change of combustion for butyric acid at 298 K is -2,184 kJ/mol, and the
standard entropy change of combustion for butyric acid at 298 K is -117 J/molK .
ΔHºf (kJ/mol)
Sº (J/molK)
0
-394
0
-286
0
?
+6
+214
+131
+70.
+205
+226
C (s)
CO2 (g)
H2 (g)
H2O (l)
O2 (g)
C3H7CO2H (l)
(a) Calculate the standard enthalpy change of formation, ΔHºf, for butyric acid at 298 K.
(b) Write the correctly balanced equation for the formation of butyric acid from its elements.
(c) Calculate the standard entropy change of formation, ΔSºf, for butyric acid at 298 K..
(d) Calculate the standard free energy change of formation, ΔGºf, for butyric acid at 298 K.
*7. For the phase change:
I2 (s)  I2 (g)
ΔHº = 62.24 kJ/mol and ΔSº = 143.6 J/molK.
(a) Calculate the standard free energy change, ΔGº, for the reaction at 100.ºC, and tell if the forward
or reverse reaction is spontaneous at this temperature.
(b) Calculate the standard free energy change, ΔGº, for the reaction at 200.ºC, and tell if the forward
or reverse reaction is spontaneous at this temperature.
(c) Calculate the sublimation point of solid iodine.
EXTRA HOMEWORK 3C
1. For the reaction:
2NO2 (g) ⇆ N2O4 (g)
calculate ΔG at 298 K for each of the following conditions, and predict the direction the reaction will
shift to reach equilibrium.
(a) pNO2 = 1.0 atm and pN2O4 = 1.0 atm
(b) pNO2 = 0.21 atm and pN2O4 = 0.50 atm
(c) pNO2 = 0.29 atm and pN2O4 = 1.6 atm
2. For the reaction
3H2 (g) + N2 (g) ⇆ 2NH3 (g)
use data from the appendix to 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:
C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (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. Nitrous acid ionizes according to the following equation:
HNO2 (aq) ⇆ H+ (aq) + NO2- (aq)
At 298 K the ΔG°f for nitrous acid is -51.6 kJ/mol, and the ΔG°f for the nitrite ion is -32.2 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. Benzoic acid (C6H5CO2H) is a weak organic acid with Ka = 6.5 x 10-5 at 298 K.
(a) Write the equilibrium constant expression for the ionization of benzoic acid in water.
(b) What is molarity of the benzoate ion, C6H5CO2- ion in a 1.00 M solution of benzoic acid in water?
(c) What is the pH of the solution?
(d) What is the standard free energy change of the ionization of benzoic acid in water?
(continued on next page)
6. The solubility of tin (II) fluoride in water is 0.049 g/L at 20.ºC and 0.093 g/L at 80.°C.
(a) Calculate the Ksp for tin (II) fluoride at each temperature.
(b) Determine the heat of solution and the entropy change of solution of tin (II) fluoride by using a
van’t Hoff plot.
*7. Hydrazine is a weak base that dissociates in water according to:
N2H4 (aq) + H2O (l) ⇆ N2H5+ (aq) + OH- (aq)
The Kb for hydrazine at 298 K is 2.4 x 10-6. and aqueous hydrazine has a standard free energy of
formation of 128 kJ/mol. Calculate the standard free energy of formation of the hydrazinium ion.
*8. The tables below contain information for determining thermodynamic properties of the following
reaction:
C2H5Cl (g) + Cl2 (g) → C2H4Cl2 (g) + HCl (g)
ΔGºf (kJ/mol) at 298 K
C2H5Cl (g)
Cl2 (g)
C2H4Cl2 (g)
HCl (g)
Bond
-61
0
-80.
-95
Bond Energy (kJ/mol) at 298 K
C-H
C-C
C-Cl
Cl-Cl
H-Cl
414
347
377
243
431
(a) Calculate the ΔGº for the reaction above, using the table of standard free energy changes of
formation.
(b) Calculate the ΔHº for the reaction above, using the table of bond energies.
(c) Calculate the ΔSº for the reaction above at 298 K.
(d) Calculate the equilibrium constant for the reaction at 298 K.
(e) What is the effect of an increase in temperature on the value of the equilibrium constant?
EXTRA 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) Ba (s) + Fe2+ (aq) → Ba2+ (aq) + Fe (s)
(b) 2Au (s) + 3Br2 (l) → 2Au3+ (aq) + 6Br- (aq)
(c) H2SO3 (aq) + H2O (l) + Pb2+ (aq) → SO42- (aq) + 4H+ (aq) + Pb (s)
(d) Cd (s) + 2H+ (aq) → Cd2+ (aq) + H2 (g)
2. Consider the cell
Zn (s) | Zn2+ (1.0 M) || Sn2+ (1.0 M) | Sn (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, Zn or Sn, will be the anode, and which metal will be the cathode?
(d) Do the electrons flow from Zn to Sn in the external circuit, or the other way?
3. Consider the cell
Ba (s) | Ba2+ (1.0 M) || Cr3+ (1.0 M) | Cr (s)
(a) Write the spontaneous chemical reaction that takes place in this cell
(b) What is Ɛº for the cell?
(c) Which metal, Ba or Cr, will be the cathode, and which metal will be the anode?
(d) Do the electrons flow from Ba to Cr in the external circuit, or the other way?
4. Find the missing standard reduction potentials for these following half reactions from Table 18.1:
MnO2 (s) + 4H+ (aq) + 2eAg+ (aq) + eI2 (s) + 2ePbSO4 (s) + 2e+
2H (aq) + VO2+ (aq) + e-
→
→
→
→
→
Mn2+ (aq) + 2H2O (l)
Ag (s)
2I- (aq)
Pb (s) + SO42- (aq)
VO2+ (aq) + H2O (l)
Ɛ ° = +1.21 V
Ɛ ° = +0.80 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 manganese (IV) oxide oxidize metallic silver?
(c) Will metallic silver reduce solid iodine?
(d) Will VO2+ oxidize manganese (II) ions to manganese (IV) oxide?
(e) Will metallic lead in a sulfate solution reduce solid iodine?
(f) Will silver ions oxidize VO2+?
(g) Will manganese (IV) oxide oxidize iodide ions?
EXTRA HOMEWORK 3E
1. Tell if the potentials for each set of half-reactions can be added to give the potential for the resulting
reaction.
(a) Ni2+ (aq) + 2e- → Ni (s)
Ca (s) → Ca2+ (aq) + 2e-
______________________________________________
2+
2+
Ni (aq) + Ca (s) → Ni (s) + Ca (aq)
(c) Sn4+ (aq) + 2e- → Sn2+ (aq)
Sn2+ (aq) + 2e- → Sn (s)
_________________________________
4+
-
Sn (aq) + 4e → Sn (s)
(b) Cu2+ (aq) + 2e- → Cu (s)
Al (s) → Al3+ (aq) + 3e-
____________________________________________________
3Cu2+ (aq) + 2Al (s) → 3Cu (s) + 2Al3+ (aq)
(d) Bi5+ (aq) + 2e- → Bi3+ (aq)
Bi3+ (aq) + 3e- → Bi (s)
________________________________
Bi5+ (aq) + 5e- → Bi (s)
2. From Table 18.1, use the potentials for the half-reactions:
Hg2 2+ (aq) + 2e- → 2Hg (s)
2Hg2+ (aq) + 2e- → Hg22+ (aq)
to calculate the potential for the half-reaction:
2Hg 2+ (aq) + 4e- → 2Hg (s)
3. Consider the cell
Mn (s) | Mn2+ (0.10 M) || Fe2+ (1.0 M) | Fe (s)
(a) Write the spontaneous chemical reaction that takes place in this cell
(b) Which metal, Mn or Fe, 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?
4. A silver-magnesium battery is set up under standard conditions with all species at unit activity. Initially,
the voltage developed by this cell is 3.17 V. As the battery is used, the concentration of the silver ion
gradually decreases, and that of the magnesium ion increases.
(a) Calculate the ratio of activities of products to reactants, Q, when the cell voltage is 3.00 V at 25°C
(b) Calculate the ratio of activities of products to reactants, Q, when the cell voltage is 0.00 V at 25°C
5. Consider the cell
Mg (s) | Mg2+ (0.0010 M) || Ag+ (0.0010 M) | Ag (s)
for which Ɛº = 3.17 V. Does the cell voltage increase, decrease, or remain the same when each of the
following changes is made?
(a) Excess 1.0 M sodium hydroxide is added to the anode compartment.
(b) Excess 1.0 M ammonia is added is added to the cathode compartment.
(continued on next page)
6. Find the standard reduction potentials for these following half reactions from Table 18.1:
SO42- (aq) + 4H+ (aq) + 2e- → H2SO3 (aq) + H2O (l)
Ag+ (aq) + e- → Ag (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) What is Ɛ° for the cell?
(c) What is the equilibrium constant for the reaction at 25°C?
(d) Calculate the ratio of activities of products to reactants, Q, that will produce a cell voltage of 0.51 V
at 25°C?
7. A standard hydrogen half-cell is coupled to a standard zinc half-cell. H2S gas is bubbled into the zinc halfcell, causing precipitation of ZnS, until a concentration of 1.14 M S2- is reached. The voltage of the cell
at this point is 1.40 V.
(a) What is Ɛ° for the hydrogen-zinc cell?
(b) What is the concentration of the zinc ions in the cell when the voltage is 1.40 V?
(d) What is the Ksp for zinc sulfide?
*8. The half-reaction listed in Table 18.1 that has a standard reduction potenetial of 1.51 V is a little off. The
two manganese half-reactions with standard reduction potentials of +1.68 V and +1.21 V, also found in
Table 18.1, can be added to provide the reaction with the given potential of +1.51 V. Calculate the
correct reduction potential for this half-reaction from the first two other manganese reactions.
EXTRA HOMEWORK 3F
1. Give the electrolysis products at the anode and cathode for each of the following liquids or solutions.
(a) KCl (l)
(b) KCl (aq)
(c) AuCl3 (l)
(d) AuCl3 (aq)
(a) KNO3 (aq)
(b) Au(NO3)3 (aq)
(c) HCl (aq)
(h) HNO3 (aq)
2. How many grams of metallic magnesium can be obtained by passing a current of 5.00 A through molten
magnesium chloride for 3.00 hours?
3. Electricity is passed through an aluminum nitrate solution for 45 minutes, depositing 0.126 g of
aluminum on the cathode. How many amperes was the current?
4. An aqueous solution of gold (III) nitrate is electrolyzed by passing a current of 10.0 A through an
electrolysis cell for a certain length of time. In this process 12.5 g of gold 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 oxygen gas is liberated at the anode?
EXTRA 3A ANSWERS
1. (a) liquid water
(b) gaseous propane
(c) white tin
(d) aqueous Mg(NO3)2
2. (a) +, increase
(b) -, decrease
(c) -, decrease
(d) +, increase
3. (a) positive
(b) negative
(c) negative
(d) positive
(e) positive
(f) negative
4. 82 kJ/mol; the change in enthalpy (or the amount of heat absorbed) when one mole of NO2 (g) is formed
under standard conditions via the following reaction: ½N2 (g) + O2 (g)  N2O (g)
5. 220 J/molK; the amount of entropy (or disorder) contained in one mole of NO2 (g) under standard
conditions
6. (a) -167 J/K
(b) 103 J/K
*7. 1/256
EXTRA 3B ANSWERS
1. (a) -18 kJ
(b) -18 J/K
(c) 60. J/K
(d) 42 J/K
(c) spontaneous
(d) can’t be determined
(e) forward
2. (a) can’t be determined (b) nonspontaneous
3. 104 kJ/mol; the change in Gibbs free energy (or the amount of energy available for work, or the
direction of spontaneity) for the reaction: ½N2 (g) + O2 (g) ⇆ N2O (g) when a reaction vessel contains
one-half mole of N2 (g), one mole of O2 (g), and one mole of NO2 (g) under standard conditions
4. (a) 100. kJ
(e) no
5. (a) 5.6 kJ, reverse
*6. (a) -536 kJ
(c) -527 J/K
*7. (a) 8.65 kJ, reverse
(b) 138 J/K
(c) 53 kJ
(f) ∆H against, ∆S for (g) more
(b) -0.1 kJ, forward
(c) 352 K = 78ºC
(b) 4C (s) + 4H2 (g) + O2 (g) → C3H7CO2H (l)
(d) -379 kJ
(b) -5.71 kJ, forward
(c) 433 K or 160.ºC
(d) 59 kJ (≈ 53 kJ)
EXTRA 3C ANSWERS
1. (a) -6000 J, shift right
(b) 0 J, no shift
(c) 1000 J, shift left
2. (a) -34 kJ
(b) yes
(c) 9.1 x 105
3. (a) -1324 kJ
(b) yes
(c) 8.49 x 10231 or e534 (d) products
(e) less
4. (a) 19.4 kJ
(f) more
(b) 3.98 x 10-4
5. (a) Ka = [H3O+][C6H5CO2-]/[C6H5CO2H]
(c) 2.10
(c) 3.98 x 10-4 ≈ 4.0 x 10-4
(b) 8.0 x 10-3 M
(d) 24 kJ
6. (a) 1.2 x 10-10, 8.4 x 10-10
(b) 28 kJ, -96 J/K
*7. -15 kJ/mol
*8. (a) -115 kJ
(b) -151 kJ
(c) -0.120 kJ/K
(d) 1.50 X 1020
(c) nonspontaneous
(d) spontaneous
(e) Keq will decrease with increasing T
EXTRA 3D ANSWERS
1. (a) spontaneous
(b) nonspontaneous
2. (a) Zn + Sn2+ → Zn2+ + Sn
(c) anode Zn, cathode Sn
3. (a) 3Ba + 2Cr3+ → 3Ba2+ + 2Cr
(c) anode Ba, cathode Cr
4. (a) MnO2 ox. agent, Pb with SO42- red. agent
(d) no
(e) yes
(b) 0.62 V
(d) Zn to Sn
(b) 2.17 V
(d) Ba to Cr
(b) yes
(c) no
(f) no
(g) yes
EXTRA 3E ANSWERS
1. (a) yes
(b) yes
(c) no
(d) no
2. 0.86 V
3. (a) Mn + Fe2+ → Mn2+ + Fe
(c) 0.74 V
(b) Mn anode, Fe cathode
(d) 0.77 V
4. (a) 5.6 x 105
(b) 1.43 x 10107 or e247
5. (a) increase
(b) decrease
6. (a) H2SO3 + H2O + 2Ag+ → SO42- + 4H+ + 2Ag
20
(c) 1.9 x 10
7. (a) 0.76 V
(b) 0.60 V
(d) 1000
(b) 2.3 x 10-22
(c) 2.6 x 10-22
*8. 1.49 V
EXTRA 3F ANSWERS
1. (a) Cl2 (g), K (s)
(b) Cl2 (g), H2 (g)
(c) Cl2 (g), Au (s)
(d) Cl2 (g), Au (s)
(e) O2 (g), H2 (g)
(f) O2 (g), Au (s)
(g) Cl2 (g), H2 (g)
(h) O2 (g), H2 (g)
2. 6.80 g
3. 0.50 A
4. (a) Au3+ + 3e- → Au
(c) 30.6 min
(b) 2H2O → O2 + 4e- + 4H+
(d) 1.52 g