Q: A 5.00 g sample of an unknown gas occupies 2.50 L at 1.00 atm and 300 K. What is the molar mass of the gas?

$$M = \frac{mRT}{PV} = \frac{5.00 \times 0.08206 \times 300}{1.00 \times 2.50} = 49.2\ \mathrm{g/mol}$$

Q: A gas sample has a density of $$1.96\ \mathrm{g/L} at$$ $$2.00\ \mathrm{atm}$$ and $$273\ \mathrm{K}. $$What is its molar mass?

$$M = \frac{dRT}{P} = \frac{1.96 \times 0.08206 \times 273}{2.00} = 21.9\ \mathrm{g/mol}$$

Q: A 1.00 L flask contains 0.50 mol of $$N_2$$ and 0.50 mol of $$O_2 at 298 K. If $$the total pressure is 2.00 atm, what is the partial pressure of $$N_2$$?

$$P_{N_2$} = X_{N_2$} P_t = 0.5 \times 2.00 = 1.00\ \mathrm{atm}$$

Question 1

Which of the following statements best explains why gases are highly compressible compared to liquids and solids?

Accepted Answer

Gas molecules have negligible volume compared to the total volume they occupy.

Question 2

A sample of oxygen gas occupies 10.0 L at 2.00 atm and 300 K. What volume will it occupy at 1.00 atm and 300 K, assuming ideal behavior?

Accepted Answer

$$20.0\ \mathrm{L}$$

Question 3

Which equation correctly relates the pressure, volume, temperature, and amount of an ideal gas?

Accepted Answer

$$PV = nRT$$

Question 4

A weather balloon filled with helium rises in the atmosphere. As it rises, the external pressure decreases. What happens to the volume of the balloon if the temperature remains constant?

Accepted Answer

The volume increases.

Question 5

Which of the following gases will effuse most rapidly through a small hole at the same temperature?

Accepted Answer

Hydrogen ($$H_2)$$

Question 6

A 5.00 g sample of an unknown gas occupies 2.50 L at 1.00 atm and 300 K. What is the molar mass of the gas?

Accepted Answer

$$M = \frac{mRT}{PV} = \frac{5.00 	imes 0.08206 	imes 300}{1.00 	imes 2.50} = 49.2\ \mathrm{g/mol}$$

Question 7

Which of the following best describes the relationship between the average kinetic energy of gas molecules and temperature?

Accepted Answer

Average kinetic energy is directly proportional to the absolute temperature.

Question 8

A mixture contains 2.0 mol of $$N_2$$ and 3.0 mol of $$O_2 in a 10.0 L $$container at 300 K. What is the mole fraction of $$O_2$$?

Accepted Answer

$$\chi_{O_2$} = \frac{3.0}{2.0 + 3.0} = 0.60$$

Question 9

Which of the following is NOT an assumption of the kinetic-molecular theory for ideal gases?

Accepted Answer

Gas molecules experience significant attractive and repulsive forces.

Question 10

A gas sample has a density of $$1.96\ \mathrm{g/L} at$$ $$2.00\ \mathrm{atm}$$ and $$273\ \mathrm{K}. $$What is its molar mass?

Accepted Answer

$$M = \frac{dRT}{P} = \frac{1.96 	imes 0.08206 	imes 273}{2.00} = 21.9\ \mathrm{g/mol}$$

Question 11

Which of the following best explains why real gases deviate from ideal behavior at high pressures?

Accepted Answer

The volume of gas molecules becomes significant compared to the container volume.

Question 12

According to Graham’s law, if $$H_2$$ and $$O_2$$ are allowed to effuse under identical conditions, what is the ratio of their rates ($$r_{H_2$}/r_{O_2$}$$)?

Accepted Answer

$$\sqrt{\frac{M_{O_2$}}{M_{H_2$}}} = \sqrt{\frac{32}{2}} = 4.0$$

Question 13

A 1.00 L flask contains 0.50 mol of $$N_2$$ and 0.50 mol of $$O_2 at 298 K. If $$the total pressure is 2.00 atm, what is the partial pressure of $$N_2$$?

Accepted Answer

$$P_{N_2$} = X_{N_2$} P_t = 0.5 	imes 2.00 = 1.00\ \mathrm{atm}$$

Question 14

Which of the following gases would have the highest root-mean-square speed ($$u_{rms}) at 298 K$$?

Accepted Answer

Helium ($$He)$$

Question 15

A gas sample is collected over water at 25°C and 1 atm total pressure. If the vapor pressure of water at 25°C is 24 mmHg, what is the partial pressure of the dry gas?

Accepted Answer

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

Question 16

Which of the following best describes diffusion?

Accepted Answer

The spread of one substance throughout a space or a second substance.

Question 17

If the temperature of a gas is doubled at constant pressure, what happens to its volume?

Accepted Answer

The volume doubles.

Question 18

Which of the following is a correct statement about the behavior of real gases?

Accepted Answer

Real gases behave ideally at high temperature and low pressure.

Gases: Properties, Laws, and Behavior

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