movement of an atom or molecule from a region of relatively high concentration to one of relatively low concentration (discussed in this chapter with regard to gaseous species, but applicable to species in any phase)

transfer of gaseous atoms or molecules from a container to a vacuum through very small openings

Graham’s law of effusion

rates of diffusion and effusion of gases are inversely proportional to the square roots of their molecular masses

average distance a molecule travels between collisions

amount of gas diffusing through a given area over a given time

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Chemistry 2e · 9.4 Effusion and Diffusion of Gases

Effusion and Diffusion of Gases: practice problems

5 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 81
A balloon filled with helium gas takes 6 hours to deflate to 50% of its original volume. How long will it take for an identical balloon filled with the same volume of hydrogen gas (instead of helium) to decrease its volume by 50%?
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Exercises 83
Starting with the definition of rate of effusion and Graham’s finding relating rate and molar mass, show how to derive the Graham’s law equation, relating the relative rates of effusion for two gases to their molecular masses.
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Exercises 85
Which of the following gases diffuse more slowly than oxygen? F₂, Ne, N₂O, C₂H₂, NO, Cl₂, H₂S
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Exercises 87
Calculate the relative rate of diffusion of ¹H₂ (molar mass 2.0 g/mol) compared with ²H₂ (molar mass 4.0 g/mol) and the relative rate of diffusion of O₂ (molar mass 32 g/mol) compared with O₃ (molar mass 48 g/mol).
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Exercises 89
When two cotton plugs, one moistened with ammonia and the other with hydrochloric acid, are simultaneously inserted into opposite ends of a glass tube that is 87.0 cm long, a white ring of NH₄Cl forms where gaseous NH₃ and gaseous HCl first come into contact.
$NH_{3} (g) + HCl (g) ⟶ NH_{4} Cl (s)$ At approximately what distance from the ammonia moistened plug does this occur? (Hint: Calculate the rates of diffusion for both NH₃ and HCl, and find out how much faster NH₃ diffuses than HCl.)
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Key terms · 5

diffusion: movement of an atom or molecule from a region of relatively high concentration to one of relatively low concentration (discussed in this chapter with regard to gaseous species, but applicable to species in any phase)
effusion: transfer of gaseous atoms or molecules from a container to a vacuum through very small openings
Graham’s law of effusion: rates of diffusion and effusion of gases are inversely proportional to the square roots of their molecular masses
mean free path: average distance a molecule travels between collisions
rate of diffusion: amount of gas diffusing through a given area over a given time

Learn 9.4 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 9.4 in the textbook · This section on openstax.org

Effusion and Diffusion of Gases: practice problems

5 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 81

A balloon filled with helium gas takes 6 hours to deflate to 50% of its original volume. How long will it take for an identical balloon filled with the same volume of hydrogen gas (instead of helium) to decrease its volume by 50%?

Exercises 83

Starting with the definition of rate of effusion and Graham’s finding relating rate and molar mass, show how to derive the Graham’s law equation, relating the relative rates of effusion for two gases to their molecular masses.

Exercises 85

Which of the following gases diffuse more slowly than oxygen? F₂, Ne, N₂O, C₂H₂, NO, Cl₂, H₂S

Exercises 87

Calculate the relative rate of diffusion of ¹H₂ (molar mass 2.0 g/mol) compared with ²H₂ (molar mass 4.0 g/mol) and the relative rate of diffusion of O₂ (molar mass 32 g/mol) compared with O₃ (molar mass 48 g/mol).

Exercises 89

When two cotton plugs, one moistened with ammonia and the other with hydrochloric acid, are simultaneously inserted into opposite ends of a glass tube that is 87.0 cm long, a white ring of NH₄Cl forms where gaseous NH₃ and gaseous HCl first come into contact.

$NH_{3} (g) + HCl (g) ⟶ NH_{4} Cl (s)$ At approximately what distance from the ammonia moistened plug does this occur? (Hint: Calculate the rates of diffusion for both NH₃ and HCl, and find out how much faster NH₃ diffuses than HCl.)

Key terms · 5

diffusion: movement of an atom or molecule from a region of relatively high concentration to one of relatively low concentration (discussed in this chapter with regard to gaseous species, but applicable to species in any phase)
effusion: transfer of gaseous atoms or molecules from a container to a vacuum through very small openings
Graham’s law of effusion: rates of diffusion and effusion of gases are inversely proportional to the square roots of their molecular masses
mean free path: average distance a molecule travels between collisions
rate of diffusion: amount of gas diffusing through a given area over a given time

Learn 9.4 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 9.4 in the textbook · This section on openstax.org