There are 3 assumptions about gas in the Molecular Theory.
- The particles in gas are considered to be small, hard spheres.
- They have insignificant volume unless it is a real gas.
- The motion of the particles in a gas are rapid, constant and random. Always in a straight line.
- All collisions between particles in a gas are perfectly elastic. The kinetic energy is never lost. Unless it is a real gas.
There is evidently no repulsion or attraction between particles. Also, the temperature and kinetic energy is proportional.
To have Ideal Gas, you have to have all the above with high temperatures, low pressure and non-polar gasses.