Question 1

Which of the following statements best explains why the vapor pressure of a liquid increases with temperature?

Accepted Answer

As temperature increases, a greater fraction of molecules have kinetic energy greater than the minimum needed to escape into the vapor phase.

Question 2

Refer to the phase diagram provided. What phase change occurs when a substance at low temperature and high pressure is heated at constant pressure, crossing the solid-liquid boundary?

Accepted Answer

Melting (fusion)

Question 3

A sample of water is heated from -30.0 °C to 200.0 °C at 1 atm. Which equation would you use to calculate the heat required to melt the ice at 0.0 °C?

Accepted Answer

$$q = n \Delta H_{fus}$$

Question 4

Which property of water is responsible for the solid/liquid boundary in its phase diagram sloping to the left, unlike most other substances?

Accepted Answer

Solid water (ice) is less dense than liquid water.

Question 5

Given the Clausius-Clapeyron equation $$\ln \frac{P_2$}{P_1$} = -\frac{\Delta H_{vap}}{R} \left( \frac{1}{T_2$} - \frac{1}{T_1$} \right)$$, what is the physical meaning of $$\Delta H_{vap}$$?

Accepted Answer

The energy required to vaporize one mole of liquid at constant pressure.

Question 6

A 5.00 g sample of water is heated from -30.0 °C to 0.0 °C. The specific heat of ice is 2.09 J/g°C. How much heat is required for this step?

Accepted Answer

$$q = (5.00\,g)(2.09\,J/g^\circ C)(0.0 - (-30.0))$$

Question 7

Which of the following best describes a supercritical fluid?

Accepted Answer

A state where the substance has properties intermediate between those of a gas and a liquid.

Question 8

The vapor pressure of acetone at its normal boiling point (329.3 K) is 1 atm. Using the Clausius-Clapeyron equation, what is the vapor pressure at 25.0 °C (298.15 K) if $$\Delta H_{vap} = 30.3 kJ/$$mol? (Use $$R = 8.3145 J/$$mol·K)

Accepted Answer

About 616 torr

Question 9

Which of the following best explains why ethylene glycol has a much higher boiling point than ethyl ether, as seen in the vapor pressure vs. temperature graph?

Accepted Answer

Ethylene glycol has stronger intermolecular forces than ethyl ether.

Question 10

A phase diagram shows a substance at its triple point. Which of the following is true?

Accepted Answer

Solid, liquid, and gas phases are all in equilibrium.

Question 11

Which of the following steps requires the greatest amount of energy for 1 mole of water at 1 atm: heating ice from -30 °C to 0 °C, melting ice at 0 °C, heating water from 0 °C to 100 °C, or vaporizing water at 100 °C?

Accepted Answer

Vaporizing water at 100 °C

Question 12

Which of the following best describes what happens to the number of molecules with enough kinetic energy to escape a liquid as temperature increases, according to the kinetic energy distribution graph?

Accepted Answer

It increases.

Question 13

Which equation would you use to calculate the heat required to vaporize 2.0 moles of acetone at its boiling point, given $$\Delta H_{vap}$$?

Accepted Answer

$$q = n \Delta H_{vap}$$

Question 14

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

Accepted Answer

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

Question 15

A sample of acetone is heated from 300.0 K to 350.0 K at 1 atm. Which of the following steps does NOT occur during this process?

Accepted Answer

Melting solid acetone at 178.5 K

Question 16

Which of the following best describes the process of sublimation?

Accepted Answer

A solid changes directly to a gas without passing through the liquid phase.

Question 17

Which of the following is the correct formula for calculating the heat required to heat 1.0 mole of acetone (molar mass = 58.08 g/mol) from 300.0 K to 329.3 K, given $$C_s = 124.5 J/$$mol·K?

Accepted Answer

$$q = (1.0\,mol)(124.5\,J/mol\cdot K)(329.3 - 300.0)$$

Phase Transitions, Vapor Pressure, and Phase Diagrams: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards