Chemistry 116: General Chemistry

SyracuseUniversity Project Advance

Exam #3, Spring 2007

NameDate

The last page of the examination are reference tables.

[Gas constant = 0.00831 kJ/mol K; 1 faraday = 96.5 kJ/V mol e-]

1)What is the thermodynamic quantity that provides the criterion for the spontaneity of a chemical reaction?

a)

b)

c)

d)

e)

2) The total entropy of a system and its surroundings always increases for a spontaneous process. This is a statement of

a)the first law of thermodynamics.

b)the law of constant composition.

c)the second law of thermodynamics.

d)the law of conservation of matter.

e)the third law of thermodynamics.

3) Which of the following has the LOWEST value of the absolute entropy per mole?

a)gaseous sodium at 900°C and 1 atm

b)gaseous sodium at 900°C and 0.5 atm

c)liquid sodium at 100°C

d)solid sodium at 30°C

e)a solid solution of sodium in potassium at 30°C

4) Which of the following processes would be expected to have a positivevalue?

a)I2(g) I2(s)

b)2NO(g) + O2(g) 2NO2(g)

c)2ClBr(g) Cl2(g) + Br2(g)

d)NH4HS(s) NH3(g) + H2S(g)

e)2H2(g) + O2(g) 2H2O(g)

5) For the reaction below H = 131.3 kJ and S = 133.6 J/K. Assuming H and S do not

vary with temperature, at what temperature will this reaction become spontaneous?

C(s) + H2O(g)  CO(g) + H2(g)

a) 273oC

b) 325oC

c) 552oC

d) 710oC

e) none of these

6) Using the thermodynamic data at 25oC, determine the value of Ho (in kJ) for the reaction.

C2H2(g) + 2H2(g)  C2H6(g)

Substance / DGof (kJ/mole) / So (J/mole)
C2H2(g) / 209 / 201
C2H4(g) / 68 / 219
C2H6(g) / -33 / 230
H2(g) / 0 / 131
H2O(g) / -229 / 189
C2H5OH(l) / -175 / 161

a) -173

b) 236

c) -311

d) -248

e) none of these

7) Calculatefor the decomposition of ozone to oxygen.

2O3(g) 3O2(g)

S° = 205 J/(mol •K) for O2(g) and 239 J/(mol •K) for O3(g) at 25°C.

a)+137 J/(mol • K)

b)–137 J/(mol • K)

c)+34 J/(mol • K)

d)–34 J/(mol •K)

e)+444 J/(mol • K)

8) For a reaction that has an equilibrium constant of 3  102, which of the following statements must be true?

a)is positive.

b)is positive.

c)is positive.

d)is negative.

e)is negative.

9) Consider the following reaction at 25oC.

C(s) + H2O(l)  CO(g) + H2(g)Go = 91.2 kJ , Ho = 131.4 kJ

What is the value of So (in J/K) for this reaction at 25oC?

a) -135

b) 1.6

c) -1.6

d) 135

e) 40

10) Condensation is a process for which

a) H and S are negative

b)H and S are positive

c) G is positive at all temperatures

d)G is negative at high temperature but positive at low temperature

e) the signs of H and S depend on the substance

11) Which of the following has a non-zero free energy of formation?

a)N2(g)

b)S8(s)

c)Fe(l)

d)Br2(l)

e)Hg(l)

12) The following reaction has G˚ = 42.6 kJ/mol at 25˚C. What is Ka for the acid HB?

HB(aq) + H2O(l) B-(aq) + H3O+(aq)

a)-17.2

b)3.41  10-8

c)1.13  10-5

d)1.63

e)14.0

13) Consider the following reactions I and II:

I.3Fe(s) + 2O2(g)  Fe3O4(s)Go = -1014.2 kJ

II.C(graphite) + O2(g)  CO2(g)Go = -394.4 kJ

What is the change in free energy, G, (in kJ) for reaction III shown below?

III.Fe3O4(s) + 2C(graphite)  3Fe(s) + 2CO2(g)

a) +1802.4

b) +619.8

c) +225.4

d) +788.2

e) -788.2

14)An oxidation-reduction reaction is one that involves at least one change of

a)formal charge.

b)oxidation potential.

c)oxidation state.

d)atomic number.

e)polarity.

15) How many electrons are involved in the following reaction?

Cl2 + 2Br-  2Cl- + Br2

a) 6

b) 2

c) 1

d) 4

e) 3

16) When the basic solution redox equation, MnO4- + CN-MnO2 + CNO-, is properly balanced, the coefficients of the reactants and products shown are, in order,

a)1, 1, 1, 1

b)1, 2, 1, 2

c)2, 1, 2, 1

d)1, 3, 1, 3

e)2, 3, 2, 3

17) Given the standard potential for the reaction of hydrogen and oxygen,

2H2+ O2 2H2OE˚ = +1.23 V

what is the standard potential for the following reaction?

H2O  H2 + (1/2)O2

a)-2.46 V

b)-1.23 V

c)-0.625 V

d)0.625 V

e)1.23 V

18) A two-compartment electrochemical cell has a silver electrode immersed in 1.0 M AgNO3 in one compartment, and a zinc electrode immersed in 1.0 M Zn(NO3)2 in the other. A salt bridge connects the two compartments, and the electrodes are connected through a voltmeter. The standard reduction potentials are

Ag+ + e- AgE˚ = +0.80 V

Zn2+ + 2e-  Zn E˚ = -0.76 V

Which of the following statements is false?

a) The silver electrode is the cathode.

b)The standard cell potential for this cell is 1.56 V.

c)The zinc electrode will lose mass, and the silver electrode will gain mass.

d)Electrons in the external circuit will flow from zinc to silver.

e)Increasing [Zn2+] will increase the cell voltage.

19)Of the following, which is the strongest reducing agent?

a)Li

b)Zn2+

c)Au

d)Cs+

e)Hg

20) Which of the following statements, referring to the reaction below, is correct?

N2(g) + 3Cl3(g)  2NCl3(g)

a) The N2 is an oxidizing agent and the Cl2 is a reducing agent.

b) The Cl2 is an oxidizing agent and the N2 is a reducing agent.

c) Both N2 and Cl2 are oxidizing agents.

d) Both N2 and Cl2 are reducing agents.

e) No oxidation or reduction occurs in this reaction.

21) For a galvanic cell with a cell potential of 1.5 V and a transfer of two electrons in the balanced chemical equation, what is the equilibrium constant at 25˚C for the net spontaneous cell reaction?

a)3.7  10-6

b)1.1  10-3

c)130

d)2.4  1025

e)5.6  1050

22) What is the voltage (in volts) of the following cell at 25oC?

Cu(s) | Cu+2 (1.0 M) || Ag+ (1.0 x 10-3 M) | Ag(s)

a) 0.11

b) 0.28

c) 0.37

d) 0.55

e) none of these

EC) For the reaction: AgBr(s)  Ag+(aq) + Br-(aq). The Ksp is 7.7 x 10-13 at 25oC. Determine G for the reaction when [Ag+] = 1.0 x 10-2 and [Br-] = 1.0 x 10-3 M.

SHOW ALL WORK.

CHE 1161 Spring 2007 Exam #3