Question 1

Ice cores are used to study Earth's atmospheric conditions from thousands of years ago. Which property of trapped gases in ice cores is most directly used to estimate past temperatures, and why?

Accepted Answer

The ratio of oxygen isotopes ($$^{18}\mathrm{O}$$/^{16}$$\mathrm{O}$$), because it reflects the temperature-dependent fractionation during ice formation.

Question 2

According to the kinetic molecular theory, which statement best explains why lighter gases have higher average speeds at the same temperature?

Accepted Answer

At a given temperature, all gases have the same average kinetic energy, so lighter molecules must move faster to have the same energy.

Question 3

A sample of gas occupies 2.0 L at 1.0 atm and 300 K. If the pressure is increased to 2.0 atm and the temperature is decreased to 150 K, what will be the new volume? (Assume ideal behavior.)

Accepted Answer

0.5 L

Question 4

Which equation represents the relationship between pressure, volume, temperature, and number of moles for an ideal gas?

Accepted Answer

$$PV = nRT$$

Question 5

A hurricane strengthens as the density of water vapor in the air increases. Which formula can be used to calculate the density ($$\rho) of $$water vapor using the ideal gas law?

Accepted Answer

$$\rho = \frac{PM}{RT}$$

Question 6

Which of the following molecules can form hydrogen bonds?

Accepted Answer

NH$$_3$$

Question 7

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

Accepted Answer

Dispersion \u003c dipole-dipole \u003c hydrogen bonding

Question 8

Which statement best describes how vapor pressure is related to intermolecular forces?

Accepted Answer

Stronger intermolecular forces result in lower vapor pressure.

Question 9

Dalton’s Law of Partial Pressures states that:

Accepted Answer

The partial pressure of a gas is equal to its mole fraction times the total pressure.

Question 10

A mixture contains 2 moles of O$$_2$$ and 3 moles of N$$_2 at a $$total pressure of 5 atm. What is the partial pressure of O$$_2$$?

Accepted Answer

Question 11

Which of the following best describes the role of hydrogen bonding in living systems?

Accepted Answer

Hydrogen bonding stabilizes the three-dimensional structure of proteins and DNA.

Question 12

Which of the following statements about dispersion forces is correct?

Accepted Answer

Dispersion forces increase with increasing molecular size.

Question 13

A foam is best described as:

Accepted Answer

A dispersion of gas bubbles in a liquid or solid.

Question 14

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

Accepted Answer

Sweating for temperature regulation in humans.

Question 15

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

Accepted Answer

Gas particles exert attractive forces on each other.

Question 16

A 5.0 g sample of a gas occupies 2.0 L at 1.0 atm and 300 K. What is the molar mass of the gas? (Use $$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

61.5 g/mol

Question 17

Which scenario best illustrates the effect of molecular mass on the Boltzmann distribution of gas velocities?

Accepted Answer

At the same temperature, lighter molecules have a higher average speed and a broader distribution than heavier molecules.

Question 18

Which unit conversion is correct for pressure?

Accepted Answer

1 atm = 760 mmHg

Question 19

A gas mixture contains 0.5 mol He, 1.0 mol Ne, and 1.5 mol Ar. If the total pressure is 4 atm, what is the mole fraction and partial pressure of Ne?

Accepted Answer

Mole fraction: $$\frac{1.0}{3.0} = 0.33$$, Partial pressure: $$0.33 	imes 4 = 1.32$$ atm

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

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