Q: A sample of gas has a mass of 0.311 g, a volume of 0.225 L, a temperature of 55 °C, and a pressure of 886 mmHg. What is the molar mass of the gas? (Use $$R = 0.08206 L$$·atm/(mol·K))

$$M = \frac{mRT}{PV} = \frac{0.311 \times 0.08206 \times 328}{1.165 \times 0.225} = 31.9 g/$$mol

Q: At STP, what is the volume occupied by 2 moles of an ideal gas?

$$V = n \times 22.4 = 2 \times 22.4 = 44.8 L$$

Q: A diver breathes compressed air at a depth where the total pressure is 4 atm. What is the partial pressure of oxygen if air is 21% oxygen by volume?

$$P_{O_2$} = 0.21 \times 4 = 0.84$$ atm

Question 1

A sample of gas has a mass of 0.311 g, a volume of 0.225 L, a temperature of 55 °C, and a pressure of 886 mmHg. What is the molar mass of the gas? (Use $$R = 0.08206 L$$·atm/(mol·K))

Accepted Answer

$$M = \frac{mRT}{PV} = \frac{0.311 	imes 0.08206 	imes 328}{1.165 	imes 0.225} = 31.9 g/$$mol

Question 2

Which of the following gases will rise in air at STP? (Molar mass of air $$\approx 28 g/$$mol)

Accepted Answer

Helium ($$M = 4 g/$$mol)

Question 3

At STP, what is the volume occupied by 2 moles of an ideal gas?

Accepted Answer

$$V = n 	imes 22.4 = 2 	imes 22.4 = 44.8 L$$

Question 4

Which law states that the volume of a gas is directly proportional to its temperature at constant pressure and amount?

Accepted Answer

Charles's Law: $$V \propto T at $$constant $$P$$ and $$n$$

Question 5

A diver breathes compressed air at a depth where the total pressure is 4 atm. What is the partial pressure of oxygen if air is 21% oxygen by volume?

Accepted Answer

$$P_{O_2$} = 0.21 	imes 4 = 0.84$$ atm

Question 6

Which of the following best explains why the volume of a real gas is higher than predicted by the ideal gas law at high pressures?

Accepted Answer

The finite volume of gas molecules becomes significant at high pressures.

Question 7

Calculate the density of $$N_2$$ gas at STP. ($$M = 28.02 g/$$mol, $$V_{mol} = 22.4 L)$$

Accepted Answer

$$d = \frac{M}{V_{mol}} = \frac{28.02}{22.4} = 1.25 g/L$$

Question 8

Which of the following gases will have the highest root mean square (RMS) velocity at 298 K?

Accepted Answer

Hydrogen, $$H_2$$ ($$M = 2.016 g/$$mol)

Question 9

Which equation accounts for both the finite volume of gas molecules and intermolecular attractions in real gases?

Accepted Answer

$$\left(P + a\left(\frac{n}{V}\$$right)^2$$\right)(V - nb) = nRT$$

Question 10

Which of the following statements about diffusion and effusion is correct?

Accepted Answer

Effusion is the process by which gas molecules escape through a small hole into a vacuum.

Question 11

According to the kinetic molecular theory, what happens to the average kinetic energy of gas molecules when the temperature is doubled?

Accepted Answer

It doubles, since $$KE_{avg} = \frac{3}{2}RT$$

Question 12

Which of the following is a correct statement about the composition of dry air?

Accepted Answer

Nitrogen is the most abundant component, making up about 78% by volume.

Question 13

A gas sample contains 2 mol $$N_2$$, 1 mol $$O_2$$, and 1 mol $$Ar in a 10 L $$container at 300 K. What is the mole fraction of $$O_2$$?

Accepted Answer

$$f_{O_2$} = \frac{1}{2+1+1} = \frac{1}{4} = 0.25$$

Question 14

Which of the following best describes the mean free path of a gas molecule?

Accepted Answer

The average distance a molecule travels between collisions.

Question 15

If the temperature of a gas is increased from 273 K to 1000 K, what happens to the distribution of molecular velocities?

Accepted Answer

The average velocity increases and the distribution broadens.

Question 16

Which of the following is NOT an assumption of the ideal gas law?

Accepted Answer

Gas molecules have significant intermolecular attractions.

Question 17

A 1.00 L container holds 1.00 mol of an ideal gas at 300 K. What is the pressure inside the container? ($$R = 0.08206 L$$·atm/(mol·K))

Accepted Answer

$$P = \frac{nRT}{V} = \frac{1.00 	imes 0.08206 	imes 300}{1.00} = 24.6$$ atm

Gases II: Properties, Laws, and Real Gas Behavior

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