Q: According to Dalton's Law of Partial Pressures, which of the following equations correctly expresses the total pressure of a mixture of gases A, B, and C?

$$P_{\text{total}} = P_A + P_B + P_C$$

Q: A gas mixture contains 0.015 mole fraction $$CO_2$$, 0.18 mole fraction $$O_2$$, and 0.805 mole fraction Ar at a total pressure of 745 mm Hg. What is the partial pressure of $$O_2$$?

$$P_{O_2$} = 0.18 \times 745 = 134.1\ \mathrm{mm\ Hg}$$

Q: Which of the following is the correct formula for the mole fraction ($$X_A) of $$component A in a mixture?

$$X_A = \frac{n_A}{n_{\text{total}}}$$

Question 1

A mixture of gases in a sealed container has a total pressure of 800 mm Hg. If the mole fraction of nitrogen ($$N_2) is 0.25$$, what is the partial pressure of $$N_2 in $$the mixture?

Accepted Answer

$$200\ \mathrm{mm\ Hg}$$

Question 2

According to Dalton's Law of Partial Pressures, which of the following equations correctly expresses the total pressure of a mixture of gases A, B, and C?

Accepted Answer

$$P_{	ext{total}} = P_A + P_B + P_C$$

Question 3

A gas mixture contains 0.015 mole fraction $$CO_2$$, 0.18 mole fraction $$O_2$$, and 0.805 mole fraction Ar at a total pressure of 745 mm Hg. What is the partial pressure of $$O_2$$?

Accepted Answer

$$P_{O_2$} = 0.18 	imes 745 = 134.1\ \mathrm{mm\ Hg}$$

Question 4

If the $$CO_2 is $$removed from the mixture in the previous question, what is the new mole fraction of $$O_2$$?

Accepted Answer

$$X_{O_2$} = \frac{0.18}{0.985} = 0.183 ($$rounded to three decimals)

Question 5

Which of the following is a correct statement of the kinetic molecular theory of gases?

Accepted Answer

Gas molecules are in constant, random motion.

Question 6

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

Accepted Answer

It doubles.

Question 7

Which of the following best describes the Maxwell-Boltzmann distribution for molecular speeds as temperature increases?

Accepted Answer

The distribution broadens and the most probable speed increases.

Question 8

For two different gases at the same temperature, which gas will have a lower average speed?

Accepted Answer

The gas with the higher molar mass.

Question 9

Which of the following is the correct formula for the mole fraction ($$X_A) of $$component A in a mixture?

Accepted Answer

$$X_A = \frac{n_A}{n_{	ext{total}}}$$

Question 10

A sample of helium and neon are mixed in a container. If the partial pressure of helium is 300 mm Hg and the partial pressure of neon is 500 mm Hg, what is the mole fraction of helium in the mixture?

Accepted Answer

$$X_{He} = \frac{300}{800} = 0.375$$

Question 11

Which of the following best describes effusion?

Accepted Answer

The escape of gas molecules through a small opening under pressure.

Question 12

According to Graham's Law, the rate of effusion of a gas is:

Accepted Answer

Inversely proportional to the square root of its molar mass.

Question 13

An unknown gas effuses at a rate that is 0.468 times that of $$O_2 at $$the same temperature. What is the molar mass of the unknown gas? ($$M_{O_2$} = 32\ \mathrm{g/mol})$$

Accepted Answer

$$M_{	ext{unknown}} = \left( \frac{32}{0.468^2$} ight) = 146\ \mathrm{g/mol}$$

Question 14

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

Accepted Answer

Diffusion is the gradual mixing of two gases, while effusion is the escape of a gas through a small opening.

Question 15

Which postulate of the kinetic molecular theory explains why gases are easily compressible?

Accepted Answer

The volume of gas molecules is much smaller than the volume of the container.

Question 16

A hospital stores oxygen and nitrogen in a tank at a total pressure of 10 atm. If the mole fraction of oxygen is 0.6, what is the partial pressure of nitrogen?

Accepted Answer

$$P_{N_2$} = (1 - 0.6) 	imes 10 = 4\ \mathrm{atm}$$

Question 17

Which of the following best describes a perfectly elastic collision as assumed in the kinetic molecular theory?

Accepted Answer

No kinetic energy is lost; energy is only transferred between molecules.

Question 18

Which of the following real-world scenarios best illustrates Graham's Law of Effusion?

Accepted Answer

Hydrogen gas escapes from a small leak in a balloon faster than oxygen gas.

Question 19

If the mean free path of a gas molecule increases, what does this imply about the conditions in the container?

Accepted Answer

The pressure is lower or the gas is less dense.

Question 20

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

Accepted Answer

Gas molecules attract and repel each other strongly.

Gases: Partial Pressures, Kinetic Molecular Theory, Diffusion, Effusion, and Real Gases

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