The Gas Laws


Boyle's Law

Boyle's law states that for a given amount of gas held at a constant temperature; volume (V) inversely varies with pressure (P)

Equations for Boyle's law include:

P x V = Constant (k)

P1 x V1 = P2 x V2

Worked Example

An observation balloon is filled with helium gas to a volume of 40L at a pressure of 1 atm. Calculate the volume when the balloon rises to an altitude where the pressure is 0.2 atm, assuming the temperature remains constant.


P1 x V1 = P2 x V2

Where V1 = 40L            V2 = ?         P1 = 1 atm          P2 = 0.2 atm

So, 40 x 1 = 0.2 x V2

V2 = 40 x 1 / 0.2

     = 200L

Therefore the volume of the balloon is 2 x 10^2L at the higher altitude

Charle's Law

Charle's Law states that a given amount of gas at constant temperature, the volume of the gas is inversely proportional to its pressure. 

Basically if the volume of a fixed amount of gas at constant temperature is halved, the pressure will double.

Equations for Charle's law include:

Volume / Temperature = Constant (k)

V1 / T1 = V2 / T2

Unit Conversions:

Temperatue is expressed in Kelvin (K)


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