map
You are in Home >> Resources >> Physics and equipment >> Medical gases

# The Gas laws-summary

Created: 7/6/2005

### Boyle's Law

For a constant amount of gas at a constant temperature, the product of the pressure and volume of the gas is a constant.

P1V1 = P2V2

### Charles's Law

For a constant amount of gas at a constant pressure, the volume of the gas is directly proportional to the absolute temperature.

V1/T1 = V2/T2

### Gay-Lussac’s Law

At a given temperature and pressure, equal volumes of gas contain equal numbers of moles. This is sometimes also known as Avogadro’s law.

P1/T1=P2/T2

Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Thus, 1 mole of any gas (i.e. 6.02 x 1023 gas molecules) at 1 atmosphere pressure and 0°C occupies a volume of approximately 22.4 litres.

Each of these laws is a special case of a more general law. That general law is called the Ideal Gas Law.

P V = n R T

At standard temperature and pressure (commonly abbreviated as STP), the value of the temperature is 0°C (273 K) and the pressure is at 1 atmosphere (760 mmHg or 760 torrs or 1.01 x 105 Nm-2 [pascals] ).

This implies that at STP, 71.0 g of chlorine gas (one mole of chlorine molecules) will occupy a volume of 22.41 litres.

In addition, 44.0 g of carbon dioxide (one mole of carbon dioxide molecules) will also occupy a volume of 22.41 litres at STP.

### Dalton’s Law

Dalton's Law of Partial Pressure states that the pressure of a gas mixture is the sum of the partial pressures of the individual components of the gas mixture.

### Graham’s Law of diffusion

The rate at which gases diffuse is inversely proportional to the square root of their densities.

# Henry's Law

Henry's Law states that at a given temperature, the amount of gas dissolved in a solute is directly proportional to the pressure of the gas above the substance.

# Critical pressure

The pressure required to liquefy a vapour at its critical temperature.

Examples:

O2 50 bar
N2O 72 bar
CO2 73 bar

# Critical temperature

The temperature above which a vapour cannot be liquefied by any amount of pressure.  Above this temperature, the substance is a gas; below it, a vapour.

Examples:

O-118°C
N2O 36.5°C
CO31.0°C

ArticleDate:20050607
SiteSection: Article