Q: Which equation can be used to calculate the change in entropy for a phase transition at constant temperature?

$$\Delta S = \frac{q_{\text{rev}}}{T}$$

Q: Suppose the vapor pressure of a liquid is measured at two different temperatures. Which equation relates the change in vapor pressure to the enthalpy of vaporization?

$$\ln \left( \frac{P_2$}{P_1$} \right) = \frac{\Delta H_{\text{vap}}}{R} \left( \frac{1}{T_1$} - \frac{1}{T_2$} \right)$$

Q: Which of the following is always true for a spontaneous process in terms of entropy?

$$\Delta S_{\text{system}} + \Delta S_{\text{surr}} \u003e 0$$

Question 1

Which of the following statements best describes the point where all three phase boundaries meet in the provided phase diagram?

Accepted Answer

It is the triple point, where solid, liquid, and vapor phases coexist in equilibrium.

Question 2

Based on the phase diagram, which phase is most stable at low temperature and high pressure?

Accepted Answer

Solid

Question 3

If the pressure is held constant and the temperature is increased, which phase transition is most likely to occur first according to the diagram?

Accepted Answer

Solid to liquid

Question 4

At a pressure below the triple point, what phase change occurs when temperature is increased?

Accepted Answer

Solid directly to vapor (sublimation)

Question 5

Which of the following best describes the critical point in a phase diagram?

Accepted Answer

It is where the liquid-vapor phase boundary ends and the densities of liquid and vapor become equal.

Question 6

If a substance is at a temperature and pressure above its critical point, which phase is present?

Accepted Answer

Supercritical fluid

Question 7

Which equation can be used to calculate the change in entropy for a phase transition at constant temperature?

Accepted Answer

$$\Delta S = \frac{q_{	ext{rev}}}{T}$$

Question 8

Suppose the vapor pressure of a liquid is measured at two different temperatures. Which equation relates the change in vapor pressure to the enthalpy of vaporization?

Accepted Answer

$$\ln \left( \frac{P_2$}{P_1$} ight) = \frac{\Delta H_{	ext{vap}}}{R} \left( \frac{1}{T_1$} - \frac{1}{T_2$} ight)$$

Question 9

If the pressure inside a vessel containing water is equal to the vapor pressure of water at a given temperature, what will happen if more water is added?

Accepted Answer

The pressure remains the same.

Question 10

Which of the following is always true for a spontaneous process in terms of entropy?

Accepted Answer

$$\Delta S_{	ext{system}} + \Delta S_{	ext{surr}} \u003e 0$$

Question 11

A student observes a phase diagram with a solid-liquid boundary that slopes to the left. Which substance is most likely being represented?

Accepted Answer

Water

Question 12

Which of the following best explains why the solid-liquid boundary for water slopes to the left in its phase diagram?

Accepted Answer

The solid phase (ice) is less dense than the liquid phase.

Question 13

Which of the following is true about the equilibrium constant $$K$$ for a chemical reaction?

Accepted Answer

It changes with changes in temperature.

Question 14

For the reaction $$A(g) + 2B(g) \leftrightarrow C(g) + \frac{5}{2}D(g)$$ with $$K = 4.0$$, what is the equilibrium constant for $$2C(g) + 5D(g) \leftrightarrow 2A(g) + 4B(g) at $$the same temperature?

Accepted Answer

0.063

Question 15

A plot of $$\ln($$vapor pressure) versus $$1/T$$ for benzene shows a straight line with slope $$-3.70 	imes 10^3$ K. What is the enthalpy of vaporization of benzene?

Accepted Answer

30.8 kJ mol$$^{-1}$$

Question 16

Which of the following is true at equilibrium for the reaction $$A(aq) + B(aq) \leftrightarrow C(aq) + D(aq)$$?

Accepted Answer

Both products and reactants are formed at equal rates.

CHEM 172 Exam I – General Chemistry Equilibrium, Thermodynamics, and Solutions Guidance

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