Question 1

Which of the following molecules can form hydrogen bonds with water and is classified as polar?

Accepted Answer

CH\_3OH

Question 2

Given the following pairs, which would have the higher boiling point and why? CO\_2 or CH\_4.

Accepted Answer

CO\_2, because it has a larger molar mass and thus stronger London dispersion forces.

Question 3

Which intermolecular force is primarily responsible for the high boiling point of water compared to other group 16 hydrides?

Accepted Answer

Hydrogen bonding

Question 4

The vapor pressure of ethyl ether is 401 torr at 18.0 $^\circ$C. Calculate the vapor pressure at 32.0 $^\circ$C if the enthalpy of vaporization is 26.0 kJ/mol. Use the Clausius-Clapeyron equation.

Accepted Answer

$\ln \left( \frac{P_2}{401} \right) = -\frac{26000}{8.314} \left( \frac{1}{305.15} - \frac{1}{291.15} \right)$

Question 5

Which of the following substances is most likely to be a gas at room temperature (25 $^\circ$C) and 1 atm?

Accepted Answer

NO\_2

Question 6

The normal boiling point of carbon disulfide (CS\_2) is 46.5 $^\circ$C. What is the vapor pressure at 100 $^\circ$C if the enthalpy of vaporization is 26.74 kJ/mol?

Accepted Answer

$\ln \left( \frac{P_2}{760} \right) = -\frac{26740}{8.314} \left( \frac{1}{373.15} - \frac{1}{319.65} \right)$

Question 7

Which of the following best describes the process when a substance changes from region A to region C in the phase diagram provided?

Accepted Answer

Melting followed by vaporization

Question 8

If a sample of a substance starts at 6 atm and -50 $^\circ$C and is changed to 20 atm and 0 $^\circ$C, what phase changes (if any) occur according to the phase diagram?

Accepted Answer

Solid to liquid

Question 9

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

Accepted Answer

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

Question 10

Given the following data for 1-propanol, which method would you use to determine the enthalpy of vaporization?

Accepted Answer

Plot $\ln P$ versus $1/T$ and determine the slope.

Question 11

Which of the following compounds is most likely to have the highest boiling point?

Accepted Answer

CH\_3OH

Question 12

Which of the following best explains why CCl\_4 is nonpolar?

Accepted Answer

It has polar bonds but a symmetrical tetrahedral geometry.

Question 13

Which of the following is true about the enthalpy change when a liquid vaporizes at its boiling point?

Accepted Answer

The process is endothermic and $\Delta H_{vap}$ is positive.

Question 14

A sample of C\_4F\_8 is heated from -14.2 $^\circ$C (freezing point) to 46.5 $^\circ$C (boiling point). Which equation would you use to calculate the energy required for the temperature change in the liquid phase?

Accepted Answer

$q = m c_{liquid} \Delta T$

Question 15

Which of the following best describes the triple point on a phase diagram?

Accepted Answer

The temperature and pressure at which all three phases coexist in equilibrium.

Question 16

Which of the following substances would you expect to have the lowest vapor pressure at room temperature?

Accepted Answer

CH\_3OH

Question 17

If the enthalpy of vaporization for a substance is 27.49 kJ/mol, what is the sign of $\Delta H_{vap}$ and what does it indicate about the process?

Accepted Answer

$\Delta H_{vap}$ is positive; the process is endothermic.

Intermolecular Forces, Phase Changes, and Vapor Pressure: Study Notes for General Chemistry

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