CHEM6B Midterm 2 Review Flashcards

Flashcards based on CHEM6B Midterm 2 questions for exam review.

Which 1.0 M solution contains the most particles?

a. Sodium sulfate
b. Magnesium sulfate
c. Potassium chloride
d. Glucose
e. Ammonia

Sodium sulfate

Calculate the standard entropy of condensation of chloroform at its boiling point, 335 K. The standard molar enthalpy of vaporization of chloroform at its boiling point is 31.4 kJ·mol–1.

a. +506 J·K–1·mol–1
b. –93.7 J·K–1·mol–1
c. +93.7 J·K–1·mol–1
d. +31.4 kJ·K–1·mol–1
e. –31.3 kJ·K–1·mol–1

–93.7 J·K–1·mol–1

Calculate the molar mass of caffeine. The kf for cyclohexane is 20.1 K·kg·mol–1. 125 mg of caffeine to 100 g of cyclohexane lowered the freezing point by 0.13 K.

a. 481 g·mol–1
b. 47.8 g·mol–1
c. 193 g·mol–1
d. 19.3 g·mol–1
e. 96.5 g·mol–1

193 g·mol–1

Consider the following compounds and their free energy of formation: Which of these liquids are thermodynamically stable

2 and 4

Which has the smallest freezing point depression and the smallest boiling point elevation?

a. 1.5 m magnesium phosphate
b. 2.0 m potassium chloride
c. 1.0 m sodium chloride
d. Both B and C
e. Both A and C

1.0 m sodium chloride

Calculate the standard reaction enthalpy for the reaction NO(g) + O(g) → NO2(g) given: O2(g) → 2O(g) ΔH° = +498.4 kJ·mol–1, NO(g) + O3(g) → NO2(g) + O2(g) ΔH° = –200 kJ·mol–1 and the standard enthalpy of formation of ozone, +142.7 kJ·mol–1.

a. –306 kJ·mol–1
b. +355 kJ·mol–1
c. +592 kJ·mol–1
d. +555 kJ·mol–1
e. +192 kJ·mol–1

–306 kJ·mol–1

Which has the smallest entropy at 298 K?

a. Br2(g)
b. Cl2(g)
c. Xe(g)
d. Br2(l)
e. Kr(g)

Br2(l)

The enthalpy of fusion of H2O(s) at its normal melting point is 6.01 kJ·mol–1. What is the entropy change for freezing 1 mol of water at this temperature?

a. +20.2 J·K–1·mol–1.
b. –22.0 J·K–1·mol–1.
c. +22.0 J·K–1·mol–1
d. –20.2 J·K–1·mol–1.
e. 0 J·K–1·mol–1.

–22.0 J·K–1·mol–1

Which has the lowest standard molar entropy?

a. C(graphite)
b. C60(s)
c. C(diamond)
d. P4(s)
e. S8(s)

C(diamond)

Which statement is true?

a. A thermodynamically stable compound is a compound with a negative standard free
energy of formation.
b. Spontaneous reactions always have ΔGr° > 0.
c. Spontaneous reactions always have ΔHr° < 0.
d. Spontaneous reactions always have ΔSr° > 0.
e. Labile is a term that refers to the thermodynamic tendency of a substance to
decompose

A thermodynamically stable compound is a compound with a negative standard free energy of formation.

The freezing point of seawater is about –1.85 °C. If seawater is an aqueous solution of sodium chloride, calculate the molality of seawater. The kf for water is 1.86 K/m.

a. 3.70 m
b. 0.995 m
c. 0.497 m
d. 1.99 m
e. 3.44 m

0.995 m

Estimate the enthalpy of reaction for the combustion of methane using the bond enthalpy data.

𝐶𝐻4(𝑔) + 2𝑂2(𝑔) → 𝐶𝑂2(𝑔) + 2𝐻2𝑂(𝑔)
the standard bond enthalpies of O=O 496 kJ·mol–1, C=O 743 kJ·mol–1, and O-H 463 kJ·mol1,
C-H 412 kJ·mol–1,
a. +698 kJ·mol–1
b. –5978 kJ·mol–1
c. +175 kJ·mol–1
d. +5978 kJ·mol–1
e. –698 kJ·mol–1

–698 kJ·mol–1

Rank the standard molar entropy of the following from lowest to highest: 1. H2O(l) 2. H2O(g) 3. H2O2(l) 4. H2O2(aq)

a. 4 < 1 < 3 < 2
b. 1 < 3 < 2 < 4
c. 3 < 1 < 4 < 2
d. 2 < 4 < 3 < 1
e. 1 < 3 < 4 < 2

1<3<4<2

What happens if CO2(l) at 30 atm and 450 K is released into a room at 1 atm and 298 K?

a. The liquid and solid are in equilibrium.
b. The liquid freezes.
c. The liquid and vapor are in equilibrium.
d. The liquid vaporizes.
e. The liquid remains stable.

The liquid vaporizes.

What is the critical temperature on the provided phase diagram?

400 K

Predict the sign of the molar Gibbs free energy for the process H2O(s) → H2O(l) at 1 atm
and 1 oC, 0 oC, and –1 oC, respectively.
a. –, 0, and +
b. +, 0, and
c. +, +, and –
d. –, –, and +
e. +, 0, and +

-,0, and +

Which of the following has the smallest molar entropy at 298 K?

a. N2(g)
b. Cl2(g)
c. F2(g)
d. He(g)
e. Ne(g)

He(g)

Which of the following would have the largest calculated value of the residual entropy?

a. N2O(s)
b. CCl4(s)
c. C6H5Cl(s) (chlorobenzene)
d. FClO3(s)
e. CO(s)

C6H5Cl

Why is the entropy of vaporization of a material always smaller than its entropy of fusion?

a. Because it involves a less disordered product.
b. It is not; it is always larger.
c. Because gases are always smaller in density than their corresponding liquids or solids.
d. Because it involves a less disordered starting material.

It is not; it is always larger

Water slowly evaporates at 25 oC. Which of the following statements regarding this reaction is true?

Water slowly evaporates at 25 oC. Which of the following statements regarding this reaction
is true?
a. This reaction is spontaneous only at 100oC.
b. This is a spontaneous reaction that is enthalpy driven.
c. The signs of the reaction enthalpy and entropy, respectively, are – and –.
d. The signs of the reaction enthalpy and entropy, respectively, are + and –.
e. This is a spontaneous reaction that is entropy driven

This is a spontaneous reaction that is entropy driven.

Consider the following processes (treat all gases as ideal).
1. The pressure of 1 mol of oxygen gas is allowed to double isothermally.
2. Carbon dioxide is allowed to expand isothermally to 10 times its original volume.
3. The temperature of 1 mol of helium is increased 25 °C at constant pressure.
4. Nitrogen gas is compressed isothermally to half its original volume.
5. A glass of water loses 100 J of energy reversibly at 30 °C.
Which of these processes lead(s) to a decrease in entropy?
a. 2
b. 1 and 2
c. 1, 4, and 5
d. 3 and 4
e. 1 and 3

1, 4, and 5

Which of the following is not a state function?

a. S
b. U
c. T
d. H
e. None; they are all state functions

None; they are all state functions.

The reaction CaO(s) + H2O(l) → Ca(OH)2(s) is spontaneous at 0 oC. Predict the sign of the
reaction enthalpy and entropy, respectively.
a. – and –
b. + and –
c. + and +
d. – and 0
e. – and +

– and –

Which of the following has the lowest freezing point?

a. 1.5 m aluminum nitrate
b. 1.0 m potassium phosphate
c. 2.0 m sodium perchlorate
d. 1.5 m magnesium phosphate
e. 1.0 m aluminum sulfate

1.5 m magnesium phosphate

What relationship does the vapor pressure of a mixture have to that of a pure liquid?
a. It increases with increasing mass of solute added to the mixture.
b. There is no direct correlation without also knowing the temperature.
c. The liquid will always have a lower vapor pressure than the mixture.
d. It is proportional to the mole fraction of the liquid.

It is proportional to the mole fraction of the liquid.