Gas Laws and Properties of Gases

Gas

Word 'gas' is from Dutch word gaos.

Air Composition

Air = 78% N, 21% O.

Properties of Gases

Gases expand to fill entire container, are mostly colorless and odorless, have low density, mix uniformly to form solutions, and their volume changes with temperature and pressure.

Atmospheric Pressure

Forces exerted on everything by air in the atmosphere.

Barometer

Used to measure atmospheric pressure.

Standard Atmospheric Pressure

760 mmHg.

Torr

Gas pressure unit 'torr' is in honor of Italian chemist Torricelli.

Boyle's Law

P1V1 = P2V2; pressure and volume are inversely related.

Charles's Law

V1/T1 = V2/T2; volume and temperature (in Kelvin) are directly related.

Gay-Lussac's Law

P1/T1 = P2/T2; pressure and temperature (in Kelvin) are directly related.

Combined Gas Law

P1V1/T1 = P2V2/T2; a combination of Boyle's, Charles's, and Gay-Lussac's Laws.

Standard Temperature and Pressure (STP)

273 K, 1 atm (101.3 kPa, 760 mmHg, 760 torr, 14.7 psi, 1.01 bar).

Ideal Gas Law

PV = nRT; ideal gas conditions occur at high temperature and low pressure.

Ideal Gas Constant (R)

R = 8.31 L·kPa/mol·K, R = 0.0821 L·atm/mol·K, R = 62.4 L·torr/mol·K, R = 62.4 L·mmHg/mol·K.

Avogadro's Hypothesis

1 mol of any gas occupies 22.4 L when temperature and pressure are held constant.

Vapor

The gaseous portion of a substance present above the liquid phase of that substance.

Vapor Pressure

The pressure exerted by the vapor of a substance.

Boiling Point

The temperature at which the vapor pressure of a substance equals the atmospheric pressure above it.

Normal Boiling Point

Occurs at sea level (760 torr).

Volatile

Liquids that evaporate readily, such as rubbing alcohol, acetone, and gasoline.

Total Pressure of Gas Collected Over Water

Ptotal = Pgas collected over water + PH2O (v.p. of water at the temperature of the reaction).

Total Pressure of a Mixture of Gases

Ptotal = PA + PB + PC + ... .