CHEM 10062Exam #4Name______

Date______

Equations:G = H - TS, G = -nFE, Ecell = Eox. + Ered., E = E° ln Q, E=E°log Q, lnK=, logK=, C=ampsxsec, S=klnW,G=H-TS, S°=nS°(products)-nS°(reactants), G=G°+RTlnQ, G°=-RTlnK, K=e(-G°/RT), Gf°=nGf°(products) -  nGf°(reactants),

Constants: R = 0.0821 L-atm/mol-K = 8.314 J/K-mol, 1 V = 1J/C,

1 F = = 96,500 C/mol e = 96,500 J/V-mol e

Multiple Choice (3 pts. ea.)

____1.Use the following standard reduction potentials in V: I2 2I– , +0.54;

Br2 2Br–, +1.07; 2H+ H2, 0.00; Cu2+ Cu, +0.34; Ni2+ Ni, –0.28. Which one of the following species could be used to oxidize I– to I2?

a. Br2b. H+c. Cu2+d. Ni2+

____2.Which reaction below should have S° > 0?

a. 2H2(g) + O2(g) 2H2O(g)b. 2NO2(g) N2O4(g)

c. H+(aq) + F(aq)  HF(aq)d. BaF2(s) Ba+2(aq) + 2F2(aq)

____3.How many grams of copper metal can be obtained by passing a current of 12 amps through a solution of CuSO4 for 15 minutes?

a. 3.6 gb. 5.4 gc. 7.1 gd. 14 g

____4.Which one of the following has the greatest entropy?

a. H2O(s)b. H2O (l)c. H2O (g)d. these are all the same

____5.The electrode at which oxidation occurs is called the:

a. oxidizing agentb. cathodec. reducing agentd. anode

____6.Assuming H and S do not vary with temperature, a reaction that is not spontaneous at low temperature can become spontaneous at high temperature if H is ______and S is ______.

a. +, +b. , c. +, d. , +

____7.The standard reduction potentials of several common metal ions are listed:

Mg2+, –2.38 V; Li+, –3.04 V; Ni2+, –0.28 V; Mn2+, –1.18 V. Considering that E° for: 2H2O(l) + 2e– H2(g) + 2OH–(aq) is –0.83 V, which of the following metals may be produced via electrolysis of an aqueous solution of its nitrate?

a. magnesiumb. lithiumc. nickeld. manganese

____8.Which of the following reactions is a redox reaction?

a. Cu + S  CuSb. Pb+ 2Br– PbBr2

c. K2CrO4 + BaCl2 BaCrO4 + 2KCld. HCl + NaOH  H2O + NaCl

____9.Ammonium chloride readily dissolves into water but causes the water temperature to decrease. For this process:

a. H = , S = , G = b. H = +, S = +, G = 

c. H = , S = , G = +d. H = +, S = +, G = +

____10.Calculate the value of G° (in kJ) for this reaction at 25°C.

(R = 8.314 J/mol•K)

N2(g) + 3H2(g) 2NH3(g)K = 5.0 x 108

a. 38 kJb. –4.2 kJc. –45 kJd. –50 kJ

____11.The two electrodes Cr(s)/Cr3+(aq) and Sn(s)/Sn2+(aq) are combined to afford a spontaneous electrochemical reaction. E°cell for this reaction is:

a. +0.88 vb. –0.88 vc. +0.60 vd. –0.60 v

____12.A spontaneous electrochemical reaction has:

a. G° = 0, E° = 0, and K > 1b. G° < 0, E° > 0, and K > 1

c. G° > 0, E° < 0, and K < 1d. G° < 0, E° = 0, and K > 1

____13.The gain of electrons is called:

a. reductionb. oxidationc. disproportionationd. fractionation

____14.Consider the following reaction at 25°C. What is the value of S° for this reaction at 25°C?

C(s) + H2O(g)  CO(g) + H2(g)

G° = 91.2 kJH° = 131.4 kJ

a. –135 J/Kb. 1.6 J/Kc. -1.6 J/Kd. 135 J/K

____15.One of the differences between a voltaic cell and an electrolytic cell is that in an electrolytic cell:

a. an electric current is produced by a chemical reaction.

b. electrons flow toward the anode.

c. a non-spontaneous reaction is forced to occur.

d. O2 gas is produced at the cathode.

____16.Which substance is the oxidizing agent in the following reaction?

Pb + PbO2 + 2H2SO4 2PbSO4 + 2H2O

a. Pbb. H2SO4c. PbO2d. PbSO4

____17.The standard reduction potentials in V for Ag+ to Agº and Fe3+ to Fe2+ are +0.80 and +0.77, respectively. Calculate K, the equilibrium constant, for the following reaction at 25°C.

Ag+(aq) + Fe2+(aq) Ag(s) + Fe3+(aq)

a. 10b. 2.0c. 3.2d. 1.0

____18.Assuming H and S do not vary with temperature, at what temperature will the reaction shown below become spontaneous?

C(s) + H2O(g) CO(g) + H2(g) H = 131.3 kJ S = 133.6 J/K

a. 325ºCb. 710ºCc. 273ºCd. 552ºC

____19.Which transformation could take place at the anode of an electrochemical cell?

a. Cr3+ to Cr2O72–b. F2 to F–c. O2to H2Od. HAsO2 to As

____20.E° for the following reaction is 0.13 V. What is the value of G° (in kJ) for the reaction? Pb(s) + 2H+(aq) Pb2+(aq) + H2(g)

a. 12 kJb. 25 kJc. –12 kJd. –25 kJ

Solve the following problems showing all work. Use complete sentences for essay questions. Remember to use proper units, significant figures and rounding.

  1. a.Draw a schematic diagram of a Ag//Zn galvanic cell. Be certain to label all parts of the cell and show the directions of electron and ion flow. (10 pts.)

b. Calculate the EMF for the Ag//Zn galvanic cell above when [Ag+] = 0.00350 M and [Zn2+] = 0.125 M at 25°C. (5 pts.)

  1. Complete and balance the following equations using the half-reaction method

(5 pts ea.)

a. H2O2(aq) + BrO2(aq)  BrO2(aq) + O2(g)(basic solution)

b. MnO4-(aq) + Cl(aq)  Mn2+(aq) + Cl2(aq)(acidic solution)

  1. Calculate E°, G°, and Kc for a Br2//Cu galvanic cell (10 pts.)
  1. Use the attached table of thermodynamic data to calculate S for the reaction below, at 25°C.

4Al(s) + 3O2(g) 2Al2O3(s)