Q: A sample of gas has a pressure of 2.0 atm and a volume of 3.0 L. If the pressure is decreased to 1.0 atm at constant temperature, what will the new volume be? (Use Boyle’s Law)

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{2.0 \times 3.0}{1.0} = 6.0\ \text{L}$$

Q: Convert a pressure of 0.500 atm to mm Hg.

$$0.500 \times 760 = 380\ \text{mm Hg}$$

Q: A mixture of gases contains 70% nitrogen and 30% oxygen by volume. If the total pressure is 2.0 atm, what is the partial pressure of oxygen?

$$P_{O_2$} = 0.30 \times 2.0 = 0.60\ \text{atm}$$

Q: A sample of gas has a mass of 0.250 g, a volume of 0.100 L, a pressure of 1.00 atm, and a temperature of 273 K. What is the molar mass of the gas? (Use the ideal gas law)

$$n = \frac{PV}{RT} = \frac{1.00 \times 0.100}{0.0821 \times 273} = 0.00447\ \text{mol}$$; Molar mass $$= \frac{0.250}{0.00447} = 56.0\ \text{g/mol}$$

Q: A scuba diver breathes a gas mixture containing 1.5% oxygen at a total pressure of 8.0 atm. What is the partial pressure of oxygen?

$$P_{O_2$} = 0.015 \times 8.0 = 0.12\ \text{atm}$$

Q: A sample of hydrogen gas is collected over water at 25°C. The total pressure is 750 mm Hg, and the vapor pressure of water at 25°C is 23.8 mm Hg. What is the partial pressure of hydrogen?

$$P_{H_2$} = 750 - 23.8 = 726.2\ \text{mm Hg}$$

Question 1

According to the kinetic molecular theory, which of the following statements best explains why gases are compressible?

Accepted Answer

There is a lot of empty space between gas particles compared to their size.

Question 2

A mercury barometer measures atmospheric pressure by the height of mercury in a glass tube. If the atmospheric pressure is 1 atm, what is the height of the mercury column?

Accepted Answer

760 mm

Question 3

Which of the following conditions favors ideal gas behavior?

Accepted Answer

High temperature and low pressure

Question 4

A sample of gas has a pressure of 2.0 atm and a volume of 3.0 L. If the pressure is decreased to 1.0 atm at constant temperature, what will the new volume be? (Use Boyle’s Law)

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{2.0 	imes 3.0}{1.0} = 6.0\ 	ext{L}$$

Question 5

A gas sample has a volume of 2.5 L at 25°C. If the temperature is increased to 75°C at constant pressure, what happens to the volume? (Use Charles’s Law)

Accepted Answer

The volume increases because temperature increases.

Question 6

Convert a pressure of 0.500 atm to mm Hg.

Accepted Answer

$$0.500 	imes 760 = 380\ 	ext{mm Hg}$$

Question 7

A mixture of gases contains 70% nitrogen and 30% oxygen by volume. If the total pressure is 2.0 atm, what is the partial pressure of oxygen?

Accepted Answer

$$P_{O_2$} = 0.30 	imes 2.0 = 0.60\ 	ext{atm}$$

Question 8

A sample of gas has a mass of 0.250 g, a volume of 0.100 L, a pressure of 1.00 atm, and a temperature of 273 K. What is the molar mass of the gas? (Use the ideal gas law)

Accepted Answer

$$n = \frac{PV}{RT} = \frac{1.00 	imes 0.100}{0.0821 	imes 273} = 0.00447\ 	ext{mol}$$; Molar mass $$= \frac{0.250}{0.00447} = 56.0\ 	ext{g/mol}$$

Question 9

Which of the following is NOT a property predicted by the kinetic molecular theory for gases?

Accepted Answer

Gas particles attract each other strongly.

Question 10

A scuba diver breathes a gas mixture containing 1.5% oxygen at a total pressure of 8.0 atm. What is the partial pressure of oxygen?

Accepted Answer

$$P_{O_2$} = 0.015 	imes 8.0 = 0.12\ 	ext{atm}$$

Question 11

A sample of hydrogen gas is collected over water at 25°C. The total pressure is 750 mm Hg, and the vapor pressure of water at 25°C is 23.8 mm Hg. What is the partial pressure of hydrogen?

Accepted Answer

$$P_{H_2$} = 750 - 23.8 = 726.2\ 	ext{mm Hg}$$

Question 12

Which equation represents the ideal gas law?

Accepted Answer

$$PV = nRT$$

Question 13

A 5.0-L sample of gas at 2.0 atm and 300 K contains how many moles of gas? (Use the ideal gas law)

Accepted Answer

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

Question 14

At STP, what is the volume occupied by 2.5 moles of an ideal gas?

Accepted Answer

$$2.5 	imes 22.4 = 56.0\ 	ext{L}$$

Question 15

A mixture of helium, neon, and argon has a total pressure of 600 mm Hg. If the partial pressure of helium is 350 mm Hg and neon is 150 mm Hg, what is the partial pressure of argon?

Accepted Answer

$$P_{Ar} = 600 - 350 - 150 = 100\ 	ext{mm Hg}$$

Question 16

Which of the following is a consequence of nonideal gas behavior?

Accepted Answer

Intermolecular interactions become significant at low temperature and high pressure.

Question 17

A reaction produces 0.50 mol of CO$$_2$$ gas at STP. What volume does this gas occupy?

Accepted Answer

$$0.50 	imes 22.4 = 11.2\ 	ext{L}$$

Question 18

A sample of gas has an initial volume of 100 mL at a pressure of 800 mm Hg and a temperature of 300 K. If the volume changes to 150 mL and the temperature increases to 350 K, what is the final pressure? (Use the combined gas law)

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$V_2$$ $$T_1$$} = \frac{800 	imes 100 	imes 350}{150 	imes 300} = 622\ 	ext{mm Hg}$$

Study Notes: Gases and Their Properties (Chapter 11, Introductory Chemistry)

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