Q: A 2.0 L flask contains 0.5 mol of $$\mathrm{O_2$}$$ and 0.5 mol of $$\mathrm{N_2$} at 300 K. $$What is the total pressure in the flask? $$(R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

$$P_T = \frac{(0.5 + 0.5) \times 0.0821 \times 300}{2.0} = 6.16\ \mathrm{atm}$$

Q: If the mole fraction of $$\mathrm{CO_2$} in a $$gas mixture is 0.25 and the total pressure is 800 mmHg, what is the partial pressure of $$\mathrm{CO_2$}$$?

$$P_{CO_2$} = 0.25 \times 800 = 200\ \mathrm{mmHg}$$

Q: A sample of air contains 78% $$\mathrm{N_2$}$$, 21% $$\mathrm{O_2$}$$, and 1% other gases by mole. If the total atmospheric pressure is 1.00 atm, what is the partial pressure of $$\mathrm{O_2$}$$?

$$P_{O_2$} = 0.21 \times 1.00 = 0.21\ \mathrm{atm}$$

Q: A 0.50 mol sample of $$\mathrm{O_2$}$$ and a 0.25 mol sample of $$\mathrm{CO_2$}$$ are placed in a 10.0 L container at 300 K. What is the total pressure?

$$P_T = \frac{(0.50 + 0.25) \times 0.0821 \times 300}{10.0} = 1.73\ \mathrm{atm}$$

Q: A gas mixture contains 2.0 mol $$\mathrm{He}$$ and 3.0 mol $$\mathrm{Ne} in a 5.0 L $$container at 400 K. What is the partial pressure of $$\mathrm{Ne}$$? $$(R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

$$P_{Ne} = \frac{3.0 \times 0.0821 \times 400}{5.0} = 19.7\ \mathrm{atm}$$

Question 1

Which of the following 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.

Question 2

A 2.0 L flask contains 0.5 mol of $$\mathrm{O_2$}$$ and 0.5 mol of $$\mathrm{N_2$} at 300 K. $$What is the total pressure in the flask? $$(R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$P_T = \frac{(0.5 + 0.5) 	imes 0.0821 	imes 300}{2.0} = 6.16\ \mathrm{atm}$$

Question 3

If the mole fraction of $$\mathrm{CO_2$} in a $$gas mixture is 0.25 and the total pressure is 800 mmHg, what is the partial pressure of $$\mathrm{CO_2$}$$?

Accepted Answer

$$P_{CO_2$} = 0.25 	imes 800 = 200\ \mathrm{mmHg}$$

Question 4

Which equation correctly relates the partial pressure of a gas to its mole fraction in a mixture?

Accepted Answer

$$P_A = X_A P_T$$

Question 5

A sample of air contains 78% $$\mathrm{N_2$}$$, 21% $$\mathrm{O_2$}$$, and 1% other gases by mole. If the total atmospheric pressure is 1.00 atm, what is the partial pressure of $$\mathrm{O_2$}$$?

Accepted Answer

$$P_{O_2$} = 0.21 	imes 1.00 = 0.21\ \mathrm{atm}$$

Question 6

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 7

A mixture of gases contains 0.2 mol $$\mathrm{H_2$}$$, 0.3 mol $$\mathrm{N_2$}$$, and 0.5 mol $$\mathrm{O_2$}. $$What is the mole fraction of $$\mathrm{N_2$}$$?

Accepted Answer

$$X_{N_2$} = \frac{0.3}{1.0} = 0.3$$

Question 8

A 5.0 L container holds a mixture of $$\mathrm{N_2$}$$ and $$\mathrm{O_2$} at 27$$°C and a total pressure of 2.0 atm. If the partial pressure of $$\mathrm{N_2$} is 1.2 $$atm, what is the partial pressure of $$\mathrm{O_2$}$$?

Accepted Answer

$$P_{O_2$} = 2.0 - 1.2 = 0.8\ \mathrm{atm}$$

Question 9

Which of the following statements is true about nonreacting gases in a mixture?

Accepted Answer

Each gas behaves as if it is alone in the container.

Question 10

A 0.50 mol sample of $$\mathrm{O_2$}$$ and a 0.25 mol sample of $$\mathrm{CO_2$}$$ are placed in a 10.0 L container at 300 K. What is the total pressure?

Accepted Answer

$$P_T = \frac{(0.50 + 0.25) 	imes 0.0821 	imes 300}{10.0} = 1.73\ \mathrm{atm}$$

Question 11

A gas mixture contains 2.0 mol $$\mathrm{He}$$ and 3.0 mol $$\mathrm{Ne} in a 5.0 L $$container at 400 K. What is the partial pressure of $$\mathrm{Ne}$$? $$(R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$P_{Ne} = \frac{3.0 	imes 0.0821 	imes 400}{5.0} = 19.7\ \mathrm{atm}$$

Question 12

A 1.0 L flask contains a mixture of 0.10 mol $$\mathrm{H_2$}$$, 0.20 mol $$\mathrm{N_2$}$$, and 0.30 mol $$\mathrm{O_2$} at 273 K. $$What is the mole fraction of $$\mathrm{O_2$}$$?

Accepted Answer

$$X_{O_2$} = \frac{0.30}{0.10 + 0.20 + 0.30} = 0.5$$

Question 13

A chemist collects hydrogen gas over water at 25°C. The total pressure is 755 mmHg and the vapor pressure of water at 25°C is 24 mmHg. What is the pressure of the dry hydrogen gas?

Accepted Answer

$$P_{H_2$} = 755 - 24 = 731\ \mathrm{mmHg}$$

Question 14

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

Accepted Answer

Collecting gases over water in laboratory experiments

Question 15

A 0.819 g sample of $$\mathrm{$$PCl_5$$} is $$placed in a 2.00 L flask and completely vaporized at 252°C. What is the pressure in the flask if no chemical reaction occurs? $$(M_{$$PCl_5$$} = 208.2\ \mathrm{g/mol},\ R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$n = \frac{0.819}{208.2} = 0.00393\ \mathrm{mol}$$, $$P = \frac{0.00393 	imes 0.0821 	imes 525}{2.00} = 0.0846\ \mathrm{atm}$$

Dalton’s Law of Partial Pressures and Gas Mixtures

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