Exam 3

Question 1

The phase diagram for xenon has a solid-liquid curve with a positive slope. Which of the following is true?

Answer 1

Solid xenon has a higher density than liquid xenon.

Question 2

Pentane, C5H12, boils at 35°C. Which of the following is true about kinetic energy, Ek, and potential energy, Ep, when liquid pentane at 35°C is compared with pentane vapor at 35°C?

Answer 2

Ep(g) > Ep(l); Ek(g) ≈ Ek(l)

Question 3

Examine the phase diagram for the substance Bogusium (Bo) and select the correct statement.

Answer 3

Point B represents the critical temperature and pressure for Bo.

Positive slope = Bo (s) has a higher density than Bo (l)

Question 4

Neon atoms are attracted to each other by

Answer 4

London dispersion forces.

Question 5

Which of the following atoms should have the greatest polarizability?
A)F
B)Br
C)Po
D)Pb
E) He

Answer 5

D) Pb

Polarizability increases down a group but decreases across a period as increasing Zeff makes atoms smaller and it more difficult to remove electrons

Cations are less polarizable
Anions are more polarizable

Question 6

Which one of the following substances will have hydrogen bonds between molecules?

A)(CH3)3N
B)CH3–O–CH3
C)CH3CH2–OH
D)CH3CH2–F
E)HI

Answer 6

C) CH3CH2–OH

Hydrogen bonding is the ability of a O, N, F bonded with a hydrogen to form bonds with hydrogens on adjacent molecules

Question 7

Intermolecular forces increase _________ (up/down) group which follows a similar trend as boiling point increases _________ (up/down) a group.

Answer 7

IMF increases down group with increasing molar mass and more electrons.

Boiling point increases with increasing molecular force as the molecules are held more tightly and less are in the

Question 8

Which of the following pairs is arranged with the particle of higher polarizability listed first?

A)Se2−, S2−
B)I, I−
C)Mg2+, Mg
D)Br, I
E)None of these choices are correct.

Answer 8

A)Se2−, S2−

Polarizability increases down a group
Anion is more polarizable than cation

Question 9

Which of the following should have the highest boiling point?

A)CF4
B)CCl4
C)CBr4
D)CI4

Answer 9

D)CI4

Boiling point increases with IMF which increases with molar mass

Question 10

When the electron cloud of a molecule is easily distorted, the molecule has a high:

Answer 10

polarizability

Question 11

Which of the following atoms should have the smallest polarizability?

A)Si
B)S
C)Te
D)Bi
E)Br

Answer 11

B) S

Question 12

Which of the following pairs is arranged with the particle of higher polarizability listed first?

A)CCl4, CI4
B)H2O, H2Se
C)C6H14, C4H10
D)NH3, NF3
E)None of these choices are correct.

Answer 12

C)C6H14, C4H10

Question 13

Which of the following should have the lowest boiling point?

A)C5H12
B)C6H14
C)C8H18
D)C10H22
E)C12H26

Answer 13

IMF increases with molar mass. Lowest molar mass = lowest boiling point for like compounds

Question 14

Which of the following results in a decrease in the entropy of the system?

A)O2(g), 300 K → O2(g), 400 K
B)H2O(s), 0°C → H2O(l), 0°C
C)N2(g), 25°C → N2(aq), 25°C
D)NH3(l), −34.5°C → NH3(g), −34.5°C
E)2H2O2(g) → 2H2O(g) + O2(g)

Answer 14

C)N2(g), 25°C → N2(aq), 25°C

Entropy decreases from gas to liquid to solid

Gas to liquid to solid is exothermic

solid to liquid to gas is endothermic

Question 15

Which of the following should have the greatest molar entropy at 298 K?

A)CH4(g)
B)H2O(l)
C)NaCl(s)
D)N2O4(g)
E)H2(g)

Answer 15

D)N2O4(g)

Gasses will have the highest entropies

Larger molecules in the same group will have more energy levels in a condensed level thereby increasing the entropy.

Entropy increases with number of atoms in the compound.

Question 16

For allotropes, entropy is higher in the form which:

Answer 16

Allows for greater freedom of motion

Question 17

Which of the following is true for a system at equilibrium?

A)ΔS°sys = ΔS°surr
B)ΔS°sys = −ΔS°surr
C)ΔS°sys = ΔS°surr = 0
D)ΔS°univ > 0
E) None of these choices are correct.

Answer 17

B)ΔS°sys = −ΔS°surr

Question 18

Which of the following is always true for an exothermic process?

A)qsys > 0, ΔSsurr < 0
B)qsys < 0, ΔSsurr > 0
C)qsys < 0, ΔSsurr < 0
D)qsys > 0, ΔSsurr > 0
E)w < 0

Answer 18

B)qsys < 0, ΔSsurr > 0

Question 19

Which relationship or statement best describes ΔS° for the following reaction?

HgS(s) + O2(g) → Hg(l) + SO2(g)

A)ΔS° ≈ 0
B)ΔS° < 0
C)ΔS° > 0
D)ΔS° = ΔH°/T
E)More information is needed to make a reasonable prediction.

Answer 19

C)ΔS° > 0

Question 20

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

A)CO(g), CO2(g)
B)NaCl(s), NaCl(aq)
C)H2S(g), H2S(aq)
D)Li(s), Pb(s)
E)H2(g), H2O(g)

Answer 20

C)H2S(g), H2S(aq)

Entropy of gas > entropy solution

Question 21

Which one of the following phase changes decreases the entropy of the system?

A)Melting
B)Heating a gas
C)Vaporization
D)Condensation
E)Sublimation

Answer 21

Correct answer D)Condensation (gas->liquid)

Melting (solid to liquid) increases entropy

Heating a gas causes molecules to have more kinetic energy increasing number of microstates

Vaporization (liquid to gas) increases entropy

Sublimation (solid to gas) increases entropy

Question 22

For a chemical reaction to be spontaneous only at low temperatures, which of the following conditions must be met?

A)ΔS° > 0, ΔH° > 0
B)ΔS° > 0, ΔH° < 0
C)ΔS° < 0, ΔH° < 0
D)ΔS° < 0, ΔH° > 0
E)ΔG° > 0

Answer 22

C)ΔS° < 0, ΔH° < 0

ΔG°=ΔH°-ΔS°T

Question 23

For a chemical reaction to be non-spontaneous at any temperature, which of the following conditions must be met?

A)ΔS° > 0, ΔH° > 0
B)ΔS° > 0, ΔH° < 0
C)ΔS° < 0, ΔH° < 0
D)ΔS° < 0, ΔH° > 0
E)All reactions are spontaneous at some temperature.

Answer 23

D)ΔS° < 0, ΔH° > 0

Question 24

Consider the following balanced redox reaction:

Mn2+(aq) + S2O82−(aq) + 2H2O(l) → MnO2(s) + 4H(aq) + 2SO42−(aq)

Which of the following statements is true?

A)Mn2+(aq) is the oxidizing agent and is reduced.

B)Mn2+(aq) is the oxidizing agent and is oxidized.

C)Mn2+(aq) is the reducing agent and is oxidized.

D)Mn2+(aq) is the reducing agent and is reduced.

E)Manganese does not change its oxidation number in this reaction.

Answer 24

C)Mn2+(aq) is the reducing agent and is oxidized.

Question 25

When the following redox equation is balanced with smallest whole number coefficients, the coefficient for the hydrogen sulfate ion will be

Al(s) + HSO4(aq) + OH−(aq) → Al2O3(s) + S2−(aq) + H2O(l)

1.
3.
4.
8.
None of these choices are correct.

Answer 25

3

Question 26

A voltaic cell is prepared using copper and silver. Its cell notation is shown below.

Cu(s) | Cu2+(aq) || Ag+(aq) | Ag(s)

Which of the following processes occurs at the cathode?

A) Cu(s) → Cu2+(aq) + 2e−
B) Cu2+(aq) + 2e− → Cu(s)
C) Ag(s) → Ag+(aq) + e−
D) Ag+(aq) + e− → Ag(s)Correct
E) Cu(s) + 2Ag+(aq) → Cu2+(aq) + 2Ag(s)

Answer 26

D) Ag+(aq) + e− → Ag(s)

An OXidation
Rededuction CAT

Question 27

Consider the nonaqueous cell reaction

2Na(l) + FeCl2(s) ⇄ 2NaCl(s) + Fe(s)

for which E°cell = 2.35 V at 200°C. Calculate ΔG° at this temperature:

Answer 27

ΔG°=(-n)(F)(E°cell)

-453 kJ

Question 28

The value of the equilibrium constant for the reaction of nickel(II) ions with cadmium metal is 1.17 × 105. Calculate ΔG° for the reaction at 25°C.

Answer 28

ΔG°=-RT ln K

-29 kJ

Question 29

A concentration cell consists of two Zn/Zn2+ electrodes. The electrolyte in compartment A is 0.10 M Zn(NO3)2 and in compartment B is 0.60 M Zn(NO3)2. What is the voltage of the cell at 25°C?

Answer 29

E°cell= -(0.05916/n) * log [Dil]/[Conc]