Question 1

Which equation is used to relate the vapor pressure of a liquid to its temperature, allowing the calculation of enthalpy of vaporization ($\Delta H_{vap}$)?

Accepted Answer

$\ln P = -\frac{\Delta H_{vap}}{RT} + C$

Question 2

Given the following vapor pressures of benzene at two temperatures: $P_1 = 602.0$ mmHg at $T_1 = 300$ K and $P_2 = 932.0$ mmHg at $T_2 = 320$ K, use the Clausius-Clapeyron equation to estimate $\Delta H_{vap}$ in kJ/mol.

Accepted Answer

$\Delta H_{vap} \approx 34.1$ kJ/mol

Question 3

Cyclooctane has a heat of vaporization of $43.3$ kJ/mol and a normal boiling point of $149\ ^\circ$C. At what temperature will it boil if the external pressure is $565$ torr?

Accepted Answer

$365$ K

Question 4

Ethanol has a heat of vaporization of $38.56$ kJ/mol and a normal boiling point of $78.4\ ^\circ$C. What is the vapor pressure of ethanol at $23\ ^\circ$C?

Accepted Answer

$73$ torr

Question 5

A solid crystallizes into two forms: $\alpha$-solid and $\beta$-solid. Using the phase diagram, which solid state is less dense?

Accepted Answer

$\beta$-solid

Question 6

In a phase diagram, what does the point where the fusion curve, vaporization curve, and sublimation curve meet represent?

Accepted Answer

Triple point

Question 7

Which of the following statements is correct regarding the heat of sublimation, heat of vaporization, and heat of fusion at the same temperature?

Accepted Answer

The heat of sublimation is equal to the sum of the heat of vaporization and heat of fusion.

Question 8

Which of the following best describes the process of deposition in a phase diagram?

Accepted Answer

Transition from gas to solid

Question 9

A substance melts at $75\ ^\circ$C and boils at $115\ ^\circ$C. Which heating curve best represents the temperature change as heat is added from $50\ ^\circ$C to $250\ ^\circ$C?

Accepted Answer

A curve with two plateaus, one at $75\ ^\circ$C and one at $115\ ^\circ$C, with temperature rising before, between, and after the plateaus.

Question 10

Calculate the amount of heat released (in kJ) when $35.0$ g of benzene vapor is cooled from $96.0\ ^\circ$C to $26.4\ ^\circ$C. Given: $b.p. = 80.09\ ^\circ$C$, \Delta H_{vap} = 30.72$ kJ/mol, $m.p. = 5.49\ ^\circ$C$, \Delta H_{fus} = 9.87$ kJ/mol, $C_{liq} = 136.0$ J/(mol $^\circ$C), $C_{vap} = 82.4$ J/(mol $^\circ$C).

Accepted Answer

$-24.2$ kJ

Question 11

Which statement is correct regarding phase changes as pressure is increased from $0.05$ atm to $15$ atm at $100\ ^\circ$C?

Accepted Answer

Only one phase change occurs.

Question 12

Which of the following is true about the critical point in a phase diagram?

Accepted Answer

It is the temperature and pressure above which a liquid and gas are indistinguishable.

Question 13

If the freezing point of a solid decreases as pressure is increased, what does this indicate about the relative densities of the solid and liquid?

Accepted Answer

The solid is less dense than the liquid.

Question 14

Which curve in a phase diagram represents the equilibrium between solid and liquid phases?

Accepted Answer

Fusion curve

Question 15

What is the effect of increasing temperature at constant pressure on the phase of a substance?

Accepted Answer

Solid $\rightarrow$ Liquid $\rightarrow$ Gas

Question 16

Which of the following best describes a supercritical fluid?

Accepted Answer

A phase that exists above the critical temperature and pressure where liquid and gas are indistinguishable.

Question 17

Which process requires the most energy per mole: melting, vaporization, or sublimation?

Accepted Answer

Sublimation

Question 18

If a substance is at its triple point, which phases are present?

Accepted Answer

Solid, liquid, and gas

Question 19

Which of the following statements is true about the normal boiling point of a liquid?

Accepted Answer

It is the temperature at which the vapor pressure equals $1$ atm.

Liquids, Solids, and Intermolecular Forces: Clausius-Clapeyron Equation, Phase Diagrams, and Heating/Cooling Curves

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