Q: A sample of oxygen gas is collected over water at 25°C and 1 atm. If the vapor pressure of water at 25°C is 24 mm Hg, what is the partial pressure of the oxygen gas in atm?

$$P_{O_2$} = 1.00\ \text{atm} - \frac{24\ \text{mm Hg}}{760\ \text{mm Hg/atm}} = 0.968\ \text{atm}$$

Q: A 5.00 L container holds 2.00 mol of nitrogen gas at 300 K. What is the pressure inside the container? (Use $$R = 0.0821\ \text{L} \cdot \text{atm} / \text{mol} \cdot \text{K})$$

$$P = \frac{nRT}{V} = \frac{2.00 \times 0.0821 \times 300}{5.00} = 9.85\ \text{atm}$$

Q: A mixture contains 2.0 mol of helium and 3.0 mol of neon in a 10.0 L container at 298 K. What is the total pressure of the mixture? ($$R = 0.0821\ \text{L} \cdot \text{atm} / \text{mol} \cdot \text{K})$$

$$P = \frac{5.0 \times 0.0821 \times 298}{10.0} = 12.2\ \text{atm}$$

Q: A sample of gas has a density of $$1.96\ \text{g/L} at$$ $$2.00\ \text{atm}$$ and $$273\ \text{K}. $$What is the molar mass of the gas?

$$M = \frac{dRT}{P} = \frac{1.96 \times 0.0821 \times 273}{2.00} = 21.9\ \text{g/mol}$$

Q: Which of the following is the correct expression for Dalton’s Law of Partial Pressures for a mixture of non-reacting gases?

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

Question 1

Which of the following statements best explains why gases are highly compressible compared to solids and liquids?

Accepted Answer

Gas molecules are in continuous, random motion and occupy negligible volume compared to the total volume.

Question 2

A sample of oxygen gas is collected over water at 25°C and 1 atm. If the vapor pressure of water at 25°C is 24 mm Hg, what is the partial pressure of the oxygen gas in atm?

Accepted Answer

$$P_{O_2$} = 1.00\ 	ext{atm} - \frac{24\ 	ext{mm Hg}}{760\ 	ext{mm Hg/atm}} = 0.968\ 	ext{atm}$$

Question 3

Which of the following correctly describes the relationship between pressure and volume for a fixed amount of gas at constant temperature (Boyle’s Law)?

Accepted Answer

$$P V = 	ext{constant}$$

Question 4

A 5.00 L container holds 2.00 mol of nitrogen gas at 300 K. What is the pressure inside the container? (Use $$R = 0.0821\ 	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot 	ext{K})$$

Accepted Answer

$$P = \frac{nRT}{V} = \frac{2.00 	imes 0.0821 	imes 300}{5.00} = 9.85\ 	ext{atm}$$

Question 5

Which of the following is NOT an assumption of the kinetic-molecular theory of gases?

Accepted Answer

Gas molecules experience significant attractive and repulsive forces.

Question 6

A mixture contains 2.0 mol of helium and 3.0 mol of neon in a 10.0 L container at 298 K. What is the total pressure of the mixture? ($$R = 0.0821\ 	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot 	ext{K})$$

Accepted Answer

$$P = \frac{5.0 	imes 0.0821 	imes 298}{10.0} = 12.2\ 	ext{atm}$$

Question 7

Which gas will effuse faster under the same conditions: ammonia ($$NH_3$$, molar mass = 17 g/mol) or carbon dioxide ($$CO_2$$, molar mass = 44 g/mol)?

Accepted Answer

Ammonia, because it has a lower molar mass.

Question 8

A sample of gas has a density of $$1.96\ 	ext{g/L} at$$ $$2.00\ 	ext{atm}$$ and $$273\ 	ext{K}. $$What is the molar mass of the gas?

Accepted Answer

$$M = \frac{dRT}{P} = \frac{1.96 	imes 0.0821 	imes 273}{2.00} = 21.9\ 	ext{g/mol}$$

Question 9

Which of the following best explains why real gases deviate from ideal behavior at high pressures?

Accepted Answer

The volume of gas molecules becomes significant compared to the container volume.

Question 10

A weather balloon is filled with 10.0 L of helium at 1.00 atm and 300 K. If the balloon rises to a region where the pressure is 0.500 atm and the temperature is 250 K, what will be the new volume of the balloon?

Accepted Answer

$$V_2$$ = $$V_1$$ \frac{$$P_1$$}{$$P_2$$} \frac{$$T_2$$}{$$T_1$$} = 10.0 	imes \frac{1.00}{0.500} 	imes \frac{250}{300} = 16.7\ 	ext{L}$$

Question 11

Which of the following is the correct expression for Dalton’s Law of Partial Pressures for a mixture of non-reacting gases?

Accepted Answer

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

Question 12

A 1.00 L flask contains 0.500 mol of $$O_2$$ and 0.500 mol of $$N_2 at 298 K. $$What is the mole fraction of $$O_2 in $$the mixture?

Accepted Answer

$$X_{O_2$} = \frac{0.500}{0.500 + 0.500} = 0.500$$

Question 13

Which of the following changes will increase the average kinetic energy of a gas sample?

Accepted Answer

Increasing the temperature of the gas.

Question 14

According to Graham’s law, what is the ratio of the rates of effusion of hydrogen ($$H_2$$, molar mass = 2 g/mol) to oxygen ($$O_2$$, molar mass = 32 g/mol)?

Accepted Answer

$$	ext{Rate}_{H_2$}/	ext{Rate}_{O_2$} = \sqrt{\frac{32}{2}} = 4.0$$

Question 15

Which of the following best describes the effect of decreasing the temperature of a gas at constant volume?

Accepted Answer

The pressure decreases because the average kinetic energy of the molecules decreases.

Question 16

A real gas behaves most ideally under which of the following conditions?

Accepted Answer

High temperature and low pressure.

Question 17

Which of the following is a correct rearrangement of the ideal gas law to solve for the density of a gas?

Accepted Answer

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

Question 18

A chemical reaction produces 2.00 L of $$CO_2$$ gas at STP. How many grams of $$CO_2$$ are produced? (Molar mass of $$CO_2 = 44.0$$\ 	ext{g/mol}$$, 1$$\ 	ext{mol}$$ gas at STP = 22.4$$\ 	ext{L}$$)

Accepted Answer

$$	ext{mol} = \frac{2.00}{22.4} = 0.0893$$, $$	ext{mass} = 0.0893 	imes 44.0 = 3.93\ 	ext{g}$$

Question 19

Which of the following is a correction made by the van der Waals equation for real gases?

Accepted Answer

It accounts for the finite volume of gas molecules and intermolecular attractions.

Chapter 10: Gases – Properties, Laws, and Theories

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