Pressure Volume Temperature Relationship

Gas molecules are in constant motion.In a container the number of molecules are colliding with the walls of the container.This creates pressure.The gas molecules also occupy certain space.This is volume.

Introduction to pressure volume temperature relationship

Out of three phases of a substance i.e solid ,liquid and gas,only the gas phase exhibits the properties of pressure and volume distinctively that their correlation could be developed.

• Boyle was the first person to study and establish the correlation between pressure and volume of a gas.He noticed that ,at constant temperature,the volume of a gas varies inversely with the pressure.In a container,if the pressure on the gas is increased,the gas gets suppressed,in turn reducing the volume.So more the pressure,less the volume.He put it as under,

At constant temperature,
P=k / V  where k is constant.

Charles' Law Shows Relationship between Volume and Temperature

• Charles developed equation to find the relationship between the temperature and volume.

It says that at constant pressure,the volume of a gas is directly proportional to the temperature.
Hence,
V `alpha`
V=kT

Universal Gas Law and Ideal Gas Law Shows Relationship between Pressure Volume and Temperature

• Boyle's and Charles's law when combined,give us universal gas law,

 P1V1/T1=P2V2/T2
What is the presure at 200k ,volume 1 L, if at 1 atm and 300k the volume is 2 l.?
P1V1/T1=P2V2/T2
1 x 2/300=P₂ x 2/200
P2= 0.666 atm
This is the correlation between pressure ,volume and temperature.It is very useful in determining the value of any of the missing parameter if the other are known.

• Further more detail attempts were made and this correlation could be found for given number of quantity of a gas.Therefore,for a given number of moles of a gas,

PV=nRT

where n is number of moles of a gas,R is gas constant and T is temperature.This is the ideal gas law.
It may be remembered here that all this laws are meant to be in ideal conditions.In practice there always will be deviation.
Avogadro's number gives us relation between the number of moles/number of molecules and the volume.Thus from the above equation,pressure,or volume of a gas can be calculated if either of the number of moles/number of molecules is known.