The Jacana Technical Library

Air and Gases

General Gas Laws

Perfect Gas Law

PV=nRT

P=Pressure in atmospheres

V=Volume in litres

n=Number of moles

R=Gas constant (0.0821 litre-atmospheres / K / mole)

T=Temperature in K

If constant pressure   V1/V2 = T1/T2

If constant temperature  P1/P2 = V2/V1

If constant volume  P1/P2 = T1/T2

# Boyle’s Law

If temperature is kept constant, the volume of a given mass of gas is inversely proportional to the pressure which is exerted upon it.

Initial Pressure     Final Volume

----------------  =  --------------

Final Pressure       Initial Volume

# Charles’ Law

If the pressure is constant, the volume of a given mass of gas is directly proportional to the absolute temperature.

Initial Volume           Final Volume

---------------------  =  -------------------

Initial Temperature K     Final Temperature K

# Dalton’s Law of Partial Pressures

The pressure which is exerted on the walls of a vessel is the sum of the pressures which each gas would exert if it were presemt alone.

PV = V (p1 + p2 … pn)

# Graham’s Law of Diffusion

Relative rates of diffusion of two gases are inversely proportional to the square root of their densities.

Equal volumes of gases, measured under the same conditions of temperature and pressure, contain equal numbers of molecules.

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