Q: A sample of oxygen gas ($$\mathrm{O_2$}) is $$contained in a 5.0 L vessel at 2.0 atm and 300 K. Using the ideal gas law, what is the number of moles of oxygen present?

$$n = \frac{PV}{RT} = \frac{2.0 \times 5.0}{0.0821 \times 300} = 0.41\ \mathrm{mol}$$

Q: Which equation represents Dalton’s Law of Partial Pressures?

$$P_{\text{total}} = P_1$ + P_2$ + P_3$ + \ldots$$

Question 1

Ice cores are used to study Earth's atmospheric conditions in 'deep time.' Which of the following best explains how scientists determine the age of a specific layer in an ice core?

Accepted Answer

By analyzing the isotopic composition of water molecules and counting annual layers formed by seasonal changes.

Question 2

According to the kinetic molecular theory, which statement is TRUE regarding the distribution of molecular speeds in a gas sample?

Accepted Answer

Lighter molecules have a broader distribution of speeds compared to heavier molecules at the same temperature.

Question 3

Which of the following is NOT a postulate of the kinetic molecular theory of gases?

Accepted Answer

Gas particles exert attractive forces on each other.

Question 4

A sample of oxygen gas ($$\mathrm{O_2$}) is $$contained in a 5.0 L vessel at 2.0 atm and 300 K. Using the ideal gas law, what is the number of moles of oxygen present?

Accepted Answer

$$n = \frac{PV}{RT} = \frac{2.0 	imes 5.0}{0.0821 	imes 300} = 0.41\ \mathrm{mol}$$

Question 5

Which of the following statements about dispersion forces is CORRECT?

Accepted Answer

Dispersion forces increase with increasing molecular size.

Question 6

Which molecule below can form hydrogen bonds?

Accepted Answer

$$\mathrm{NH_3$}$$

Question 7

Rank the following intermolecular forces from weakest to strongest for small molecules: (1) dispersion, (2) dipole-dipole, (3) hydrogen bonding.

Accepted Answer

Dispersion \u003c dipole-dipole \u003c hydrogen bonding

Question 8

A hurricane strengthens as water vapor condenses and releases energy. Which property of water vapor is most directly related to this process?

Accepted Answer

The density of water vapor in the air.

Question 9

Which equation represents Dalton’s Law of Partial Pressures?

Accepted Answer

$$P_{	ext{total}} = P_1$ + P_2$ + P_3$ + \ldots$$

Question 10

A mixture contains 2.0 mol $$\mathrm{N_2$}$$ and 1.0 mol $$\mathrm{O_2$} in a 10.0 L $$container at 298 K. What is the mole fraction of $$\mathrm{O_2$}$$?

Accepted Answer

$$X_{\mathrm{O_2$}} = \frac{1.0}{2.0 + 1.0} = 0.33$$

Question 11

Which of the following best describes how vapor pressure is measured?

Accepted Answer

By sealing a liquid in a container and measuring the pressure exerted by its vapor at equilibrium.

Question 12

Which factor most directly affects the vapor pressure of a liquid?

Accepted Answer

The strength of intermolecular forces in the liquid.

Question 13

Which application of water depends most on its enthalpy of vaporization ($$\Delta H_{	ext{vap}}$$)?

Accepted Answer

Sweating for temperature regulation in humans.

Question 14

Which of the following is required for hydrogen bonding to occur between molecules?

Accepted Answer

A hydrogen atom bonded to a highly electronegative atom (N, O, or F).

Question 15

A gas sample contains 0.5 mol $$\mathrm{CO_2$}$$ and 0.5 mol $$\mathrm{H_2O} at a $$total pressure of 1.0 atm. What is the partial pressure of $$\mathrm{CO_2$}$$?

Accepted Answer

$$P_{\mathrm{CO_2$}} = X_{\mathrm{CO_2$}} 	imes P_{	ext{total}} = 0.5 	imes 1.0 = 0.5\ 	ext{atm}$$

Question 16

Which of the following best explains why hydrogen bonding is important in living systems?

Accepted Answer

It stabilizes the three-dimensional structure of proteins and DNA.

Question 17

A foam is best described as:

Accepted Answer

A colloidal dispersion of gas in a liquid.

Question 18

A 2.0 g sample of a gas occupies 1.0 L at 1.0 atm and 273 K. What is the molar mass of the gas? (Use $$R = 0.0821\ 	ext{L}\cdot	ext{atm}\cdot	ext{mol}^{-1}\cdot	ext{K}^{-1})$$

Accepted Answer

$$M = \frac{	ext{mass}}{n} = \frac{2.0}{\frac{1.0 	imes 1.0}{0.0821 	imes 273}} = 44.8\ 	ext{g/mol}$$

Question 19

Which of the following best describes the relationship between temperature and the Boltzmann distribution of molecular speeds?

Accepted Answer

As temperature increases, the average molecular speed increases and the distribution broadens.

Study Guide: Gases and Intermolecular Forces (Chapters 10 & 11)

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