STATISTICAL ENSEMBLES

ENSEMBLES : 
                          Ensembles is defined as the collection of large number of macroscopically identical but independent system. 
Here the term "macroscopic identical" means that each of the system constituting ensembles must satisfies the same macroscopic condition such as volume, pressure,energy,temperature of total number of particles.
 The term "independent system"means that the system are mutually non-interacting.

TYPE OF ENSEMBLES :
                                            1. The microcanonical ensembles 
                                            2. The canonical ensembles
                                            3. The grand canonical ensembles
1. MICRO CANONICAL ENSEMBLES : 

                                                                       It is defined as a collection of essentially independent system having the same energy E,volume V and number of particles N. All the individuals system of a microcanonical ensembles are separated by well insulated rigid walls. The values of V,E,and N for a particular system should not be affected at all by the presence of other system.Hence, energy and number of particles of system are constant.www.taakeducation.blogspot.com  

POSTULATES OF STATISTICAL PHYSICS

STATISTICAL PHYSICS IS BASED ON FOLLOWING POSTULATES :

1. Any gas is considered to be made up of molecules which are in continuous random motion         and these molecules behave like elastic spheres of extremely small size.
2. In phase space, all the cells are of small size.
3. In a macrostate, all accessible microstates are equally probable. This is called the postulate         of  equal a priori probability.
4. The equilibrium  state of a gas corresponds to the macrostate of maximum probability.
5. Total number of molecules in a system always remains constant.
6. Total energy of the system is always constant.