Question 1

According to the kinetic molecular theory, which of the following statements is NOT an assumption made about ideal gases?

Accepted Answer

There are significant attractive and repulsive forces between gas molecules.

Question 2

Which equation correctly expresses the root-mean-square speed ($$u_{rms}) of a $$gas molecule?

Accepted Answer

$$u_{rms} = \sqrt{\dfrac{3RT}{M}}$$

Question 3

A sample of hydrogen gas and a sample of oxygen gas are both at 273 K. Which statement best describes the difference in their molecular speed distributions?

Accepted Answer

Hydrogen molecules have a broader and higher-speed distribution than oxygen molecules.

Question 4

Which of the following best explains why the Kelvin temperature of a gas is directly proportional to the average kinetic energy of its molecules?

Accepted Answer

Because $$E_k = \dfrac{3}{2} \left( \dfrac{RT}{N_A} \right)$$, showing kinetic energy increases linearly with temperature.

Question 5

According to Graham's Law, if gas A has a molar mass four times that of gas B, how does the rate of effusion of gas A compare to gas B?

Accepted Answer

Gas A effuses at half the rate of gas B.

Question 6

Which of the following is a limitation of Graham's Law of effusion?

Accepted Answer

It does not apply to diffusion, only to effusion through a tiny orifice at low pressure.

Question 7

A sample of Kr(g) effuses through a tiny hole in 87.3 s. The same amount of an unknown gas escapes in 42.9 s under identical conditions. What is the molar mass of the unknown gas? (Molar mass of Kr = 83.8 g/mol)

Accepted Answer

20.1 g/mol

Question 8

Which of the following best describes the effect of repulsive forces (parameter $$b) in $$the van der Waals equation?

Accepted Answer

They increase the pressure above the ideal gas value by reducing the effective volume.

Question 9

Which of the following is the correct form of the van der Waals equation for real gases?

Accepted Answer

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

Question 10

For a real gas, the compressibility factor $$z = \dfrac{PV}{nRT} is $$found to be less than 1 at a certain pressure and temperature. What does this indicate about the intermolecular forces?

Accepted Answer

Attractive forces dominate, causing the pressure to be lower than predicted by the ideal gas law.

Question 11

Which of the following changes would increase the average kinetic energy of gas molecules in a closed container?

Accepted Answer

Increasing the temperature of the gas.

Question 12

A 0.50 mol sample of CO$$_2 is $$confined in a 10.0 L vessel at 300 K. Using the ideal gas law, what is the pressure in the vessel? ($$R = 0.0821 L$$·atm·mol$$^{-1}$$·K$$^{-1})$$

Accepted Answer

1.23 atm

Question 13

Which of the following best explains why deviations from ideal gas behavior are observed at high pressures?

Accepted Answer

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

Question 14

Which parameter in the van der Waals equation accounts for the attractive forces between molecules?

Accepted Answer

$$a$$

Question 15

If the compressibility factor $$z$$ for a gas is greater than 1, which of the following is true?

Accepted Answer

Repulsive forces dominate, and the pressure is higher than predicted by the ideal gas law.

Question 16

Which of the following gases would you expect to show the greatest deviation from ideal behavior at room temperature and 10 atm pressure?

Accepted Answer

NH$$_3$$

Question 17

A real gas is found to have a lower pressure than predicted by the ideal gas law under certain conditions. Which modification in the van der Waals equation accounts for this observation?

Accepted Answer

The $$a$$ parameter, which corrects for intermolecular attractions.

Question 18

Which of the following best describes the physical meaning of the parameter $$b in $$the van der Waals equation?

Accepted Answer

It represents the excluded volume per mole due to the finite size of gas molecules.

Question 19

Which of the following is NOT a consequence of the kinetic molecular theory for ideal gases?

Accepted Answer

Gas molecules attract each other strongly at all distances.

Chapter 6: Gases – Kinetic Molecular Theory, Molecular Speeds, Graham’s Law, and Real Gases

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