Q: A sample of nitrogen gas is collected over water at 25 °C and a total pressure of 755 mmHg. The vapor pressure of water at 25 °C is 23.8 mmHg. What is the partial pressure of nitrogen gas?

$$755 \text{ mmHg} - 23.8 \text{ mmHg} = 731.2 \text{ mmHg}$$

Q: A 2.00 L sample of gas at 1.50 atm is compressed to 1.20 L at constant temperature. What is the final pressure?

$$P_2$$ = \frac{$$P_1$$ $$V_1$$}{$$V_2$$} = \frac{1.50 \times 2.00}{1.20} = 2.50 \text{ atm}$$

Q: A sample of carbon monoxide gas occupies 3.2 L at 125 °C. At what temperature (in K) will the gas occupy 1.54 L if the pressure remains constant?

$$T_2$$ = \frac{$$V_2$$ \times $$T_1$$}{$$V_1$$} = \frac{1.54 \times 398}{3.2} = 191.5 \text{ K}$$

Q: Calculate the density (in g/L) of uranium hexafluoride ($$UF_6) at 779 $$mmHg and 62 °C. (Molar mass = 352 g/mol)

$$d = \frac{P \times \text{molar mass}}{R \times T} = \frac{1.025 \times 352}{0.082 \times 335} = 13.1 \text{ g/L}$$

Q: A mixture contains 8.24 moles of methane, 0.421 moles of ethane, and 0.116 moles of propane. If the total pressure is 1.37 atm, what is the partial pressure of ethane?

$$P_{C_2H_6} = X_{C_2H_6} \times P_{\text{total}} = \frac{0.421}{8.24 + 0.421 + 0.116} \times 1.37 = 0.065 \text{ atm}$$

Q: A 2.14-L sample of hydrogen chloride gas at 2.61 atm and 28 °C is dissolved in 668 mL of water. What is the molarity of the resulting hydrochloric acid solution?

$$n = \frac{PV}{RT} = \frac{2.61 \times 2.14}{0.082 \times 301} = 0.23 \text{ mol}$$; $$M = \frac{0.23}{0.668} = 0.344 \text{ M}$$

Question 1

Which of the following statements best explains why gases are the most compressible state of matter?

Accepted Answer

Gas molecules are far apart compared to their size, allowing them to be compressed easily.

Question 2

A sample of nitrogen gas is collected over water at 25 °C and a total pressure of 755 mmHg. The vapor pressure of water at 25 °C is 23.8 mmHg. What is the partial pressure of nitrogen gas?

Accepted Answer

$$755 	ext{ mmHg} - 23.8 	ext{ mmHg} = 731.2 	ext{ mmHg}$$

Question 3

Which law describes the relationship between the volume and pressure of a gas at constant temperature?

Accepted Answer

Boyle's Law

Question 4

A 2.00 L sample of gas at 1.50 atm is compressed to 1.20 L at constant temperature. What is the final pressure?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$}{$$V_2$$} = \frac{1.50 	imes 2.00}{1.20} = 2.50 	ext{ atm}$$

Question 5

Which of the following is NOT a postulate of the kinetic molecular theory of gases?

Accepted Answer

Gas particles attract and repel each other strongly.

Question 6

A sample of carbon monoxide gas occupies 3.2 L at 125 °C. At what temperature (in K) will the gas occupy 1.54 L if the pressure remains constant?

Accepted Answer

$$T_2$$ = \frac{$$V_2$$ 	imes $$T_1$$}{$$V_1$$} = \frac{1.54 	imes 398}{3.2} = 191.5 	ext{ K}$$

Question 7

Which equation combines Boyle's, Charles's, and Avogadro's laws into a single relationship for ideal gases?

Accepted Answer

$$PV = nRT$$

Question 8

Calculate the density (in g/L) of uranium hexafluoride ($$UF_6) at 779 $$mmHg and 62 °C. (Molar mass = 352 g/mol)

Accepted Answer

$$d = \frac{P 	imes 	ext{molar mass}}{R 	imes T} = \frac{1.025 	imes 352}{0.082 	imes 335} = 13.1 	ext{ g/L}$$

Question 9

A mixture contains 8.24 moles of methane, 0.421 moles of ethane, and 0.116 moles of propane. If the total pressure is 1.37 atm, what is the partial pressure of ethane?

Accepted Answer

$$P_{C_2H_6} = X_{C_2H_6} 	imes P_{	ext{total}} = \frac{0.421}{8.24 + 0.421 + 0.116} 	imes 1.37 = 0.065 	ext{ atm}$$

Question 10

Which of the following best describes Dalton's Law of Partial Pressures?

Accepted Answer

The total pressure of a mixture of gases is the sum of the partial pressures of each gas.

Question 11

A 2.14-L sample of hydrogen chloride gas at 2.61 atm and 28 °C is dissolved in 668 mL of water. What is the molarity of the resulting hydrochloric acid solution?

Accepted Answer

$$n = \frac{PV}{RT} = \frac{2.61 	imes 2.14}{0.082 	imes 301} = 0.23 	ext{ mol}$$; $$M = \frac{0.23}{0.668} = 0.344 	ext{ M}$$

Question 12

Which of the following gases will have the highest root-mean-square (rms) speed at 25 °C?

Accepted Answer

Hydrogen ($$H_2)$$

Question 13

The average kinetic energy of a gas particle is given by which equation?

Accepted Answer

$$KE = \frac{3}{2}RT$$

Question 14

A gas initially at 4.0 L, 1.2 atm, and 66 °C undergoes changes so that its final volume and temperature become 1.7 L and 42 °C. What is its final pressure?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$V_2$$ $$T_1$$} = \frac{1.2 	imes 4.0 	imes 315}{1.7 	imes 339} = 2.62 	ext{ atm}$$

Question 15

Which of the following best explains why gases mix evenly and completely when confined to the same container?

Accepted Answer

Gas molecules are in constant, random motion and have negligible intermolecular forces.

Question 16

What is the volume (in liters) occupied by 49.8 g of HCl at 1 atm and 0 °C? (Molar mass of HCl = 36.5 g/mol)

Accepted Answer

$$V = \frac{nRT}{P} = \frac{(49.8/36.5) 	imes 0.082 	imes 273}{1} = 30.5 	ext{ L}$$

Question 17

Which of the following is true about the relationship between temperature and the average kinetic energy of gas molecules?

Accepted Answer

As temperature increases, the average kinetic energy of gas molecules increases.

Question 18

Calculate the root-mean-square speed ($$u_{rms}) of $$nitrogen molecules at 250 K. (Molar mass of $$N_2 = 28 g/$$mol)

Accepted Answer

$$u_{rms} = \sqrt{\frac{3RT}{M}} = \sqrt{\frac{3 	imes 8.314 	imes 250}{0.028}} = 461 	ext{ m/s}$$

Study Notes: Properties and Laws of Gases (General Chemistry)

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