Q: A sample of nitrogen gas occupies 2.50 L at 1.00 atm and 25 °C. What will its volume be at 2.00 atm and 25 °C?

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{1.00 \times 2.50}{2.00} = 1.25\ \text{L}$$

Q: A gas sample has a pressure of 749 mmHg. What is this pressure in atmospheres?

$$P = \frac{749\ \text{mmHg}}{760\ \text{mmHg/atm}} = 0.985\ \text{atm}$$

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 volume (in liters) occupied by 2.12 moles of NO at 6.54 atm and 76 °C.

$$V = \frac{nRT}{P} = \frac{2.12 \times 0.082 \times (273 + 76)}{6.54} = 9.3\ \text{L}$$

Q: What is the density (in g/L) of uranium hexafluoride (UF$$_6) at 779 $$mmHg and 62 °C?

$$d = \frac{P \times \text{molar mass}}{RT} = \frac{1.025 \times 352}{0.082 \times 335} = 13.2\ \text{g/L}$$

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?

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

Q: 641 mL of hydrogen gas is collected over water at 30 °C and a total pressure of 755 mmHg. The vapor pressure of water at 30 °C is 31.82 mmHg. What is the mass of hydrogen gas collected?

$$P_{\text{H}_2$$} = 755 - 31.82 = 723.18\ \text{mmHg}$$; n$$ = \frac{PV}{RT} = \frac{(723.18/760) \times 0.641}{0.082 \times 303} = 0.0248\ \text{mol}$$; m = n$$ \times 2.016 = 0.050\ \text{g}$$

Question 1

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

Accepted Answer

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

Question 2

A sample of nitrogen gas occupies 2.50 L at 1.00 atm and 25 °C. What will its volume be at 2.00 atm and 25 °C?

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{1.00 	imes 2.50}{2.00} = 1.25\ 	ext{L}$$

Question 3

Which instrument is used to measure atmospheric pressure?

Accepted Answer

Barometer

Question 4

A gas sample has a pressure of 749 mmHg. What is this pressure in atmospheres?

Accepted Answer

$$P = \frac{749\ 	ext{mmHg}}{760\ 	ext{mmHg/atm}} = 0.985\ 	ext{atm}$$

Question 5

According to Charles’s Law, what happens to the volume of a gas if the temperature increases at constant pressure?

Accepted Answer

The volume increases.

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 of the following best describes Avogadro’s Law?

Accepted Answer

At constant pressure and temperature, the volume of a gas is proportional to the number of moles.

Question 8

Calculate the volume (in liters) occupied by 2.12 moles of NO at 6.54 atm and 76 °C.

Accepted Answer

$$V = \frac{nRT}{P} = \frac{2.12 	imes 0.082 	imes (273 + 76)}{6.54} = 9.3\ 	ext{L}$$

Question 9

What is the density (in g/L) of uranium hexafluoride (UF$$_6) at 779 $$mmHg and 62 °C?

Accepted Answer

$$d = \frac{P 	imes 	ext{molar mass}}{RT} = \frac{1.025 	imes 352}{0.082 	imes 335} = 13.2\ 	ext{g/L}$$

Question 10

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

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

Question 11

641 mL of hydrogen gas is collected over water at 30 °C and a total pressure of 755 mmHg. The vapor pressure of water at 30 °C is 31.82 mmHg. What is the mass of hydrogen gas collected?

Accepted Answer

$$P_{	ext{H}_2$$} = 755 - 31.82 = 723.18\ 	ext{mmHg}$$; n$$ = \frac{PV}{RT} = \frac{(723.18/760) 	imes 0.641}{0.082 	imes 303} = 0.0248\ 	ext{mol}$$; m = n$$ 	imes 2.016 = 0.050\ 	ext{g}$$

Question 12

Which postulate of the kinetic molecular theory explains why gases have low densities compared to liquids and solids?

Accepted Answer

Gas particles are very small compared to the average distance that separates them.

Question 13

Calculate the root-mean-square (rms) speed of O$$_2$$ molecules at 23 °C.

Accepted Answer

$$u_{	ext{rms}} = \sqrt{\frac{3RT}{M}} = \sqrt{\frac{3 	imes 8.314 	imes 296}{0.032}} = 441\ 	ext{m/s}$$

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

Question 15

Which of the following is NOT a physical characteristic of gases?

Accepted Answer

Gases are the least compressible of the states of matter.

Question 16

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

Accepted Answer

$$n = \frac{PV}{RT} = \frac{2.61 	imes 2.14}{0.082 	imes 301} = 0.23\ 	ext{mol}$$; $$M = \frac{0.23}{0.668} = 0.338\ 	ext{M}$$

Question 17

Which of the following equations correctly expresses Dalton’s Law of Partial Pressures for a mixture of gases?

Accepted Answer

$$P_{	ext{total}} = P_1$ + P_2$ + P_3$ + \ldots$$

Question 18

Which of the following gases would have the highest root-mean-square (rms) speed at the same temperature?

Accepted Answer

H$$_2$$

Study Notes: Properties and Laws of Gases (General Chemistry, Chapter 7)

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