Assumptions of the molecular kinetic theory of an ideal gas
• Molecules move randomly in straight lines in all directions and at various speeds.
• Gas molecules in random motion collide with each other and with the wall of the container. Such collisions are completely elastic.
• There are no attractions or repulsions between molecules.
• When compared with the distance between molecules, volume of molecules is considered as negligible. • When molecules collide with one another and bounce off the total kinetic energy of the system remains the same.
• The pressure exerted by a gas is the result of collisions of the molecules on the walls of the container.
Molecular kinetic equation is 
P = pressure, V = volume of gas , m = mass of a gas particle/molecule , N = number of gas particles/molecules
_ c²= mean square speed
The spreading of a certain type of molecules throughout space occupied by another type of molecules is called diffusion. Example :- When a substance with a scent is kept inside a room, diffusion takes place until the scent is distributed uniformly throughout the room.
Rate of diffusion – solids < liquids < gases
It has been experimentally found that different gases diffuse at different rates. The production of ammonium chloride by the diffusion of ammonia and hydrogen chloride molecules through air can be demonstrated by the following apparatus. From this it is clear that the rate of diffusion of ammonia molecules with a low molecular mass is higher than that of hydrogen chloride molecules.
Factors affecting the rate of diffusion of a gas – molar mass, area, concentration gradient and temperature.
Variation of the mean speed of a gas with temperature is shown by the following Maxwell – Boltzmann curves.
