Q: Which of the following is the correct formula for the average speed ($$u) of a $$gas particle according to kinetic-molecular theory?

$$u = \sqrt{\dfrac{3RT}{\text{molar mass}}}$$

Question 1

Which of the following statements best explains why gases with very different chemical properties (such as helium and oxygen) behave similarly in terms of their physical properties under the same conditions?

Accepted Answer

Because the average distance between gas particles is so large that intermolecular forces are negligible.

Question 2

A mixture of 7.0 g CO and 10.0 g SO$$_2 is $$placed in a sealed container at 0.33 atm. What is the partial pressure of CO in the container? (Molar masses: CO = 28.01 g/mol, SO$$_2 = 64.07 g/$$mol)

Accepted Answer

$$P_{CO} = 0.20 	ext{ atm}$$

Question 3

Which postulate of the kinetic-molecular theory is most responsible for the fact that the ideal gas law works well at low pressures?

Accepted Answer

The volume occupied by individual gas particles is negligible compared to the volume of the container.

Question 4

A 4.30 g sample of hydrazoic acid (HN$$_3$$, 43.03 g/mol) is placed in a 2.00 L vessel and decomposes completely at 530.15 K according to $$2	ext{HN}_3(l) ightarrow 	ext{H}_2(g) + 3	ext{N}_2(g). $$What is the final pressure in the vessel? ($$R = 0.08206 	ext{ L atm mol}^{-1} 	ext{K}^{-1})$$

Accepted Answer

$$3.26 	ext{ atm}$$

Question 5

Which of the following best describes the molecular-level explanation for Boyle's Law ($$V \propto 1/P) $$for a fixed amount of gas at constant temperature?

Accepted Answer

As volume decreases, gas particles collide more frequently with the container walls, increasing pressure.

Question 6

According to Graham's law, the rate of effusion of a gas is inversely proportional to:

Accepted Answer

The square root of its molar mass.

Question 7

Which equation correctly relates the total pressure in a mixture of unreacting gases to the partial pressures of the individual gases?

Accepted Answer

$$P_{total} = P_1$ + P_2$ + P_3$ + \dots$$

Question 8

A sample of zinc (25.5 g, 65.39 g/mol) reacts with 250.0 mL of 3.50 M HCl to produce H$$_2$$ gas. What volume of H$$_2 is $$produced at 0.976 atm and 289 K? ($$R = 0.08206 	ext{ L atm mol}^{-1} 	ext{K}^{-1})$$

Accepted Answer

$$0.438 	ext{ L}$$

Question 9

Which of the following is the correct expression for the mole fraction ($$X_i) of a $$component in a gas mixture?

Accepted Answer

$$X_i = \dfrac{n_i}{n_{total}}$$

Question 10

Which of the following statements about the kinetic energy of gas particles is true?

Accepted Answer

At the same temperature, all gas particles have the same average kinetic energy regardless of mass.

Question 11

Which of the following is the correct formula for the average speed ($$u) of a $$gas particle according to kinetic-molecular theory?

Accepted Answer

$$u = \sqrt{\dfrac{3RT}{	ext{molar mass}}}$$

Question 12

Which of the following is a reason why real gases deviate from ideal behavior at high pressures?

Accepted Answer

The volume occupied by gas particles becomes significant compared to the container volume.

Question 13

In the reaction $$4	ext{NH}_3(g) + 5	ext{O}_2(g) ightarrow 4	ext{NO}(g) + 6	ext{H}_2	ext{O}(l)$$, if 35.6 L of NH$$_3$$ and 40.5 L of O$$_2 at $$STP are reacted, which is the limiting reactant?

Accepted Answer

O$$_2$$

Question 14

Which of the following best describes the effect of increasing temperature on the distribution of molecular speeds in a gas sample?

Accepted Answer

The distribution shifts to higher speeds and becomes broader.

Question 15

Which of the following equations accounts for the non-ideal behavior of real gases by including corrections for particle volume and intermolecular attractions?

Accepted Answer

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

Question 16

Which of the following statements about the forces between gas particles is true according to the kinetic-molecular theory?

Accepted Answer

There are neither attractive nor repulsive forces between gas particles under ideal conditions.

Question 17

A mixture of gases contains 2.0 mol of O$$_2$$, 1.0 mol of N$$_2$$, and 3.0 mol of He. What is the mole fraction of He in the mixture?

Accepted Answer

$$X_{He} = 0.60$$

Question 18

If the effusion rate of an unknown gas is 1.19 times greater than that of Ar (molar mass = 39.95 g/mol), what is the molar mass of the unknown gas?

Accepted Answer

$$33.6 	ext{ g/mol}$$

Question 19

Which of the following best explains why the pressure of a gas increases when the temperature is increased at constant volume?

Accepted Answer

Gas particles move faster, causing more frequent and energetic collisions with the container walls.

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