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Section 14.4. Chemistry 14.4. Gas Mixtures & Movements. Gases: Mixtures and Movements.

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Chemistry 14 4

Section 14.4

Chemistry 14.4

Gas Mixtures & Movements

Gases mixtures and movements
Gases: Mixtures and Movements

  • A list of gear for an expedition to Mount Everest includes climbing equipment, ski goggles, a down parka with a hood, and most importantly compressed-gas cylinders of oxygen. You will find out why a supply of oxygen is essential at higher altitudes.

Dalton s law
Dalton’s Law

  • Dalton’s Law

    • How is the total pressure of a mixture of gases related to the partial pressures of the component gases?

Dalton s law1
Dalton’s Law

  • The contribution each gas in a mixture makes to the total pressure is called the partial pressure exerted by that gas.

Dalton s law2
Dalton’s Law

  • In a mixture of gases, the total pressure is the sum of the partial pressures of the individual gases in the mixture.

  • Remember, any type of pressure gauge measures total pressure, not partial pressures of the various components.

Dalton s law3
Dalton’s Law

  • Dalton’s law of partial pressures states that, at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases.

Dalton s law4
Dalton’s Law

  • Three gases are combined in container T.

Dalton s law5
Dalton’s Law

  • The partial pressure of oxygen must be 10.67 kPa or higher to support respiration in humans. The climber below needs an oxygen mask and a cylinder of compressed oxygen to survive.

Graham s law
Graham’s Law

  • Graham’s Law

    • How does the molar mass of a gas affect the rate at which the gas effuses or diffuses?

    • But first we must define effusion and diffusion.

Graham s law1
Graham’s Law

  • Diffusionis the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout.

  • For example, the smell of food cooking in the kitchen moving throughout a house, or the smell of a dead skunk spreading all around.

Graham s law2
Graham’s Law

  • Bromine vapor is diffusing upward through the air in a graduated cylinder.

Graham s law3
Graham’s Law

  • After several hours, the bromine has diffused almost to the top of the cylinder.

Graham s law4
Graham’s Law

  • During effusion, a gas escapes through a tiny hole in its container.

    • Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.

    • This means that since hydrogen is the lightest gas, it will diffuse and effuse the fastest.

Graham s law5
Graham’s Law

  • Thomas Graham’s Contribution

    • Graham’slaw of effusion states that the rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass. This law can also be applied to the diffusion of gases.

    • So, the heavier a gas, the slower it will effuse – such as a gas effusing through the walls of a balloon.

Graham s law6
Graham’s Law

  • Comparing Effusion Rates

    • A helium filled balloon will deflate sooner than an air-filled balloon because helium, He, is smaller (lighter) than oxygen, O2.

Graham s law7
Graham’s Law

  • Helium atoms are less massive than oxygen or nitrogen molecules. So the molecules in air move more slowly than helium atoms with the same kinetic energy.

Graham s law8
Graham’s Law

  • Because the rate of effusion is related only to a particle’s speed, Graham’s law can be written as follows for two gases, A and B.

Graham s law9
Graham’s Law

  • Helium effuses (and diffuses) nearly three times faster than nitrogen at the same temperature.