Q: A mixture of gases contains 0.20 mol He, 0.30 mol Ne, and 0.50 mol Ar. If the total pressure is 2.0 atm, what is the partial pressure of Ne?

$$P_{Ne} = X_{Ne} \times P_T = \frac{0.30}{1.00} \times 2.0 = 0.60$$ atm

Q: A 1.0 L flask contains 0.10 mol H$$_2$$ and 0.40 mol N$$_2 at 300 K. $$What is the total pressure in the flask? ($$R = 0.0821 L$$·atm·mol$$^{-1}$$·K$$^{-1})$$

$$P_T = \frac{(0.10+0.40) \times 0.0821 \times 300}{1.0} = 1.23$$ atm

Q: A sample of air contains 78% N$$_2$$, 21% O$$_2$$, and 1% Ar by mole. If the total pressure is 1.0 atm, what is the partial pressure of O$$_2$$?

$$P_{O_2$} = 0.21 \times 1.0 = 0.21$$ atm

Q: A 6.19 g sample of PCl$$_5 is $$vaporized in a 2.00 L flask at 252°C. If no reaction occurs, what is the pressure in the flask? (Molar mass of PCl$$_5 = 208.2 g/$$mol, $$R = 0.0821 L$$·atm·mol$$^{-1}$$·K$$^{-1})$$

$$P = \frac{nRT}{V} = \frac{(6.19/208.2) \times 0.0821 \times 525}{2.00} = 0.76$$ atm

Q: A mixture of gases in a 5.0 L container at 400 K contains 0.30 mol CO$$_2$$ and 0.70 mol N$$_2. $$What is the partial pressure of CO$$_2$$? ($$R = 0.0821 L$$·atm·mol$$^{-1}$$·K$$^{-1})$$

$$P_{CO_2$} = \frac{0.30 \times 0.0821 \times 400}{5.0} = 1.97$$ atm

Question 1

Which statement best describes Dalton's Law of Partial Pressures for a mixture of nonreacting gases?

Accepted Answer

The total pressure is the sum of the partial pressures of each gas present.

Question 2

Given a mixture of O$$_2$$, N$$_2$$, Ar, and CO$$_2 in a $$container, which of the following is true according to Dalton's Law?

Accepted Answer

Each gas exerts a pressure as if it were the only gas in the container.

Question 3

If a container holds 0.50 mol of N$$_2$$ and 0.50 mol of O$$_2 at $$the same temperature and volume, what is the mole fraction of N$$_2$$?

Accepted Answer

$$\frac{0.50}{0.50+0.50} = 0.50$$

Question 4

A mixture of gases contains 0.20 mol He, 0.30 mol Ne, and 0.50 mol Ar. If the total pressure is 2.0 atm, what is the partial pressure of Ne?

Accepted Answer

$$P_{Ne} = X_{Ne} 	imes P_T = \frac{0.30}{1.00} 	imes 2.0 = 0.60$$ atm

Question 5

Which equation correctly expresses the partial pressure of a gas in a mixture using mole fraction?

Accepted Answer

$$P_A = X_A 	imes P_T$$

Question 6

A 1.0 L flask contains 0.10 mol H$$_2$$ and 0.40 mol N$$_2 at 300 K. $$What is the total pressure in the flask? ($$R = 0.0821 L$$·atm·mol$$^{-1}$$·K$$^{-1})$$

Accepted Answer

$$P_T = \frac{(0.10+0.40) 	imes 0.0821 	imes 300}{1.0} = 1.23$$ atm

Question 7

A sample of air contains 78% N$$_2$$, 21% O$$_2$$, and 1% Ar by mole. If the total pressure is 1.0 atm, what is the partial pressure of O$$_2$$?

Accepted Answer

$$P_{O_2$} = 0.21 	imes 1.0 = 0.21$$ atm

Question 8

When collecting a gas over water, which pressure must be subtracted from the total pressure to obtain the pressure of the dry gas?

Accepted Answer

The vapor pressure of water

Question 9

A 6.19 g sample of PCl$$_5 is $$vaporized in a 2.00 L flask at 252°C. If no reaction occurs, what is the pressure in the flask? (Molar mass of PCl$$_5 = 208.2 g/$$mol, $$R = 0.0821 L$$·atm·mol$$^{-1}$$·K$$^{-1})$$

Accepted Answer

$$P = \frac{nRT}{V} = \frac{(6.19/208.2) 	imes 0.0821 	imes 525}{2.00} = 0.76$$ atm

Question 10

If PCl$$_5$$ partially dissociates in the flask at 252°C according to $$	ext{PCl}_5 ightarrow 	ext{PCl}_3 + 	ext{Cl}_2$$, and the observed pressure is 1.00 atm, what does this indicate about the system?

Accepted Answer

The total pressure is higher than if no dissociation occurred due to the formation of additional gas molecules.

Question 11

Which of the following is a real-world application of Dalton's Law of Partial Pressures?

Accepted Answer

Collecting a gas over water in a laboratory experiment

Question 12

A mixture of gases in a 5.0 L container at 400 K contains 0.30 mol CO$$_2$$ and 0.70 mol N$$_2. $$What is the partial pressure of CO$$_2$$? ($$R = 0.0821 L$$·atm·mol$$^{-1}$$·K$$^{-1})$$

Accepted Answer

$$P_{CO_2$} = \frac{0.30 	imes 0.0821 	imes 400}{5.0} = 1.97$$ atm

Question 13

If the partial pressure of O$$_2 in a $$hospital room is 0.21 atm and the total pressure is 1.00 atm, what is the mole fraction of O$$_2$$?

Accepted Answer

$$X_{O_2$} = \frac{P_{O_2$}}{P_T} = \frac{0.21}{1.00} = 0.21$$

Question 14

A gas mixture contains 2.0 mol H$$_2$$, 3.0 mol N$$_2$$, and 5.0 mol O$$_2. $$What is the mole fraction of N$$_2$$?

Accepted Answer

$$X_{N_2$} = \frac{3.0}{2.0+3.0+5.0} = 0.3$$

Question 15

Which of the following best explains why nonreacting gases in a mixture behave independently?

Accepted Answer

Each gas molecule moves and collides independently, contributing to the total pressure as if other gases were absent.

Question 16

A mixture of gases is collected over water at 25°C. The total pressure is 760 mmHg, and the vapor pressure of water at 25°C is 24 mmHg. What is the pressure of the dry gas?

Accepted Answer

$$P_{dry\ gas} = 760 - 24 = 736$$ mmHg

Question 17

If a mixture of gases in a container has partial pressures of 0.76 atm for gas A and 0.75 atm for gas B, what is the total pressure?

Accepted Answer

$$P_T = 0.76 + 0.75 = 1.51$$ atm

Question 18

A gas mixture contains 0.01 mol of A, 0.015 mol of B, and 0.025 mol of C. What is the mole percent of A?

Accepted Answer

$$\frac{0.01}{0.01+0.015+0.025} 	imes 100 = 20\%$$

Dalton’s Law of Partial Pressures and Gas Mixtures

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