There are five known phases, or states, of matter: solids, liquids, gases, and plasma and Bose-Einstein condensates.

Here we will study only three. Solid, Liquid and Gas


Only eleven elements exist as gases under normal conditions


The gaseous state is characterized by the following physical properties.

• Gases are highly compressible.

• Gases exert pressure equally in all directions.

• Gases have much lower density than the solids and liquids.

• The volume and the shape of gases are not fixed. These assume volume and shape of the container.

• Gases mix evenly and completely in all proportions without any mechanical aid (Diffusion)

Gas Laws

1. Boyle’s Law: At constant temperature




2. Charles Law:  At constant pressure


Here K is a constant that depends on the pressure of gas, the amount of gas and also unit of volume if V1 and T1 are the initial values of volume and temperature of a gas then, 


Also, if the temperature is now changed to T2 such that the volume change to V2

We can write,


3. Avogadro's Law:  At constant pressure and temperature

V   µ  n (no. of moles)  

4. Ideal gas equation

Ideal gas equation




 R = gas constant

   w = mass of gas  ρ = density

  M = Mol weight of gas  R = gas constant



5.  Modified gas equation 





 Gas Constant ‘R’


= 0.0821 lit atm/ K. mole

= 8.314x 107 erg/k. mole

= 8.314 J/k. mole

= 1.987 cal/k. mole

Units and conversion