Q: Which equation gives the root-mean-square (rms) speed of a gas molecule?

$$u_{\text{rms}} = \sqrt{\frac{3RT}{M}}$$

Q: Which of the following is the correct conversion between Celsius and Kelvin?

$$T(\text{K}) = T(\degree \text{C}) + 273.15$$

Question 1

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

Accepted Answer

Gas molecules are much farther apart than those in liquids or solids, allowing them to be pushed closer together.

Question 2

A weather balloon is filled with helium gas at ground level (1 atm, 300 K). As it rises to a region where the pressure is 0.5 atm and the temperature is 250 K, what happens to the volume of the balloon, assuming the amount of gas remains constant?

Accepted Answer

The volume increases because the pressure decreases, but the increase is partially offset by the decrease in temperature.

Question 3

Which of the following correctly expresses the relationship described by Boyle’s Law?

Accepted Answer

$$PV = 	ext{constant}$$

Question 4

A sample of gas occupies 2.0 L at 1.0 atm and 300 K. What will be its volume at 2.0 atm and 300 K, assuming ideal behavior?

Accepted Answer

1.0 L

Question 5

Which of the following is the correct value for standard atmospheric pressure in units of mm Hg?

Accepted Answer

760 mm Hg

Question 6

According to the kinetic-molecular theory, which of the following statements is TRUE for an ideal gas?

Accepted Answer

The average kinetic energy of the molecules is proportional to the absolute temperature.

Question 7

A 5.0 g sample of helium (He, $$M = 4.00 g/$$mol) and a 5.0 g sample of nitrogen (N$$_2$$, $$M = 28.0 g/$$mol) are placed in identical containers at the same temperature. Which statement is correct about their average molecular speeds?

Accepted Answer

Helium atoms move faster on average than nitrogen molecules.

Question 8

Which equation gives the root-mean-square (rms) speed of a gas molecule?

Accepted Answer

$$u_{	ext{rms}} = \sqrt{\frac{3RT}{M}}$$

Question 9

A gas is collected over water at 25°C. The total pressure is 755 mm Hg, and the vapor pressure of water at 25°C is 23.8 mm Hg. What is the partial pressure of the dry gas?

Accepted Answer

731.2 mm Hg

Question 10

Which of the following best describes Graham’s law of effusion?

Accepted Answer

The rate of effusion of a gas is inversely proportional to the square root of its molar mass.

Question 11

A helium balloon shrinks after two days. Which phenomenon best explains this observation?

Accepted Answer

Helium atoms effuse through the tiny pores in the balloon material faster than air molecules can enter.

Question 12

If the temperature of a gas is doubled (in Kelvin) at constant volume, what happens to the pressure?

Accepted Answer

The pressure doubles.

Question 13

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

Accepted Answer

Gas molecules experience significant attractive and repulsive forces.

Question 14

A 1.0 L container holds 2.0 moles of an ideal gas at 300 K. What is the pressure inside the container? (Use $$R = 0.0821 L$$·atm·mol$$^{-1}$$·K$$^{-1})$$

Accepted Answer

49.3 atm

Question 15

Which of the following best explains why the density of oxygen is lower at high altitude?

Accepted Answer

The pressure is lower, so there are fewer oxygen molecules per unit volume.

Question 16

A gas sample has a mass of 4.00 g and occupies 2.24 L at 1.00 atm and 273 K. What is the molar mass of the gas?

Accepted Answer

4.00 g/mol

Question 17

Which of the following is the correct conversion between Celsius and Kelvin?

Accepted Answer

$$T(	ext{K}) = T(\degree 	ext{C}) + 273.15$$

Question 18

If a gas is compressed to half its original volume at constant temperature, what happens to its pressure?

Accepted Answer

The pressure doubles.

Question 19

Which of the following best describes diffusion?

Accepted Answer

The movement of gas molecules from a region of high concentration to a region of low concentration.

Question 20

A rigid container holds a mixture of hydrogen and oxygen gases at the same temperature. Which statement is true about their average kinetic energies?

Accepted Answer

Both gases have the same average kinetic energy.

Study Notes: Gases (Chapter 10) – Properties, Pressure, and Gas Laws

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