Q: A sample of gas occupies 4.00 L at 1.00 atm. If the pressure is increased to 2.00 atm at constant temperature, what will be the new volume of the gas?

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{1.00 \times 4.00}{2.00} = 2.00\ \text{L}$$

Q: A manometer is used to measure the pressure of a gas in a container. If the atmospheric pressure is 760 mm Hg and the height difference in the mercury column is 50 mm (open-end manometer, gas pressure higher than atmospheric), what is the pressure of the gas?

$$P_{\text{gas}} = P_{\text{atm}} + h = 760\ \text{mm Hg} + 50\ \text{mm Hg} = 810\ \text{mm Hg}$$

Q: At STP, what is the volume occupied by 2 moles of an ideal gas?

$$V = n \times 22.4\ \text{L} = 2 \times 22.4 = 44.8\ \text{L}$$

Q: A 5.00 g sample of a gas occupies 2.00 L at 1.00 atm and 300 K. What is the molar mass of the gas?

$$M = \frac{mRT}{PV} = \frac{5.00 \times 0.0821 \times 300}{1.00 \times 2.00} = 61.6\ \text{g/mol}$$

Q: A mixture contains 2.0 mol of O$$_2$$ and 3.0 mol of N$$_2 in a 10.0 L $$container at 300 K. What is the total pressure of the mixture?

$$P = \frac{(2.0 + 3.0) \times 0.0821 \times 300}{10.0} = 12.3\ \text{atm}$$

Q: According to Graham's law, what is the ratio of the rate of effusion of helium ($$M = 4 g/$$mol) to argon ($$M = 40 g/$$mol)?

$$\text{Rate}_{\text{He}} / \text{Rate}_{\text{Ar}} = \sqrt{\frac{40}{4}} = \sqrt{10} \approx 3.16$$

Question 1

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

Accepted Answer

Gases consist of molecules with negligible volume relative to the container.

Question 2

A sample of gas occupies 4.00 L at 1.00 atm. If the pressure is increased to 2.00 atm at constant temperature, what will be the new volume of the gas?

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{1.00 	imes 4.00}{2.00} = 2.00\ 	ext{L}$$

Question 3

Which of the following is the correct SI unit for pressure?

Accepted Answer

Pa

Question 4

A manometer is used to measure the pressure of a gas in a container. If the atmospheric pressure is 760 mm Hg and the height difference in the mercury column is 50 mm (open-end manometer, gas pressure higher than atmospheric), what is the pressure of the gas?

Accepted Answer

$$P_{	ext{gas}} = P_{	ext{atm}} + h = 760\ 	ext{mm Hg} + 50\ 	ext{mm Hg} = 810\ 	ext{mm Hg}$$

Question 5

Which of the following best describes the relationship between volume and temperature for a fixed amount of gas at constant pressure?

Accepted Answer

Volume is directly proportional to absolute temperature.

Question 6

At STP, what is the volume occupied by 2 moles of an ideal gas?

Accepted Answer

$$V = n 	imes 22.4\ 	ext{L} = 2 	imes 22.4 = 44.8\ 	ext{L}$$

Question 7

Which equation correctly relates the pressure, volume, temperature, and amount of an ideal gas?

Accepted Answer

$$PV = nRT$$

Question 8

A 5.00 g sample of a gas occupies 2.00 L at 1.00 atm and 300 K. What is the molar mass of the gas?

Accepted Answer

$$M = \frac{mRT}{PV} = \frac{5.00 	imes 0.0821 	imes 300}{1.00 	imes 2.00} = 61.6\ 	ext{g/mol}$$

Question 9

A mixture contains 2.0 mol of O$$_2$$ and 3.0 mol of N$$_2 in a 10.0 L $$container at 300 K. What is the total pressure of the mixture?

Accepted Answer

$$P = \frac{(2.0 + 3.0) 	imes 0.0821 	imes 300}{10.0} = 12.3\ 	ext{atm}$$

Question 10

Which statement about the kinetic-molecular theory of gases is FALSE?

Accepted Answer

Attractive and repulsive forces between gas molecules are significant.

Question 11

If the temperature of a gas is doubled at constant volume, what happens to the pressure?

Accepted Answer

The pressure doubles.

Question 12

Which of the following gases will have the highest rate of effusion through a small hole at the same temperature?

Accepted Answer

Hydrogen ($$H_2)$$

Question 13

According to Graham's law, what is the ratio of the rate of effusion of helium ($$M = 4 g/$$mol) to argon ($$M = 40 g/$$mol)?

Accepted Answer

$$	ext{Rate}_{	ext{He}} / 	ext{Rate}_{	ext{Ar}} = \sqrt{\frac{40}{4}} = \sqrt{10} \approx 3.16$$

Question 14

Which of the following conditions will cause a real gas to deviate most from ideal behavior?

Accepted Answer

High pressure and low temperature

Question 15

Which correction does the van der Waals equation make to the ideal gas law?

Accepted Answer

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

Question 16

A gas has a density of 1.25 g/L at 1.00 atm and 273 K. What is its molar mass?

Accepted Answer

$$M = \frac{dRT}{P} = \frac{1.25 	imes 0.0821 	imes 273}{1.00} = 28.0\ 	ext{g/mol}$$

Question 17

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

Accepted Answer

The pressure decreases because molecules collide with the walls less frequently.

Question 18

A mixture of gases contains 1.0 mol $$CO_2$$, 2.0 mol $$N_2$$, and 3.0 mol $$O_2. $$What is the mole fraction of $$N_2$$?

Accepted Answer

$$X_{N_2$} = \frac{2.0}{1.0 + 2.0 + 3.0} = \frac{2.0}{6.0} = 0.33$$

General Chemistry: Chapter 10 – Gases (Study Notes)

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