Degree of freedom & first law thermodynamic

Degree of freedom

These are the total number of independent coordinate a body can have 
                                                 Or 
Total number of method of exchanging energy

For monoatomic gases

Size of particle is very-2 small ,so it does not have ratational 
Kenetic energy.

It has only 3-direction  x,y,z
Through which it can exchange energy

For diatomic gas 

It has 3-translational and 2-rotational  through which it can exchange energy

For triangular gas


It can 3-translational and 3-rotational method through which it can exchange energy

Now we will discucuss
.....................

Law of  equipartition of energy

It means energy distribution in all direction will same 
(in x , y , z direction energy will be same)

For monoatomic gases 
    In x-direction energy = kt/2
     In y-direction energy = kt/2
     In z-direction energy = kt/2
So here we can write total energy = kt/2+kt/2+kt/2
                                                              =3kt/2

Note-
Energy of rotation is equal to energy of transnational motion        

Now we will talk about the first law of thermodynamic 

Ques rises what is first law thermodynamic

first law of thermodynamics states that the increase in internal energy is equal to the total heat added and work done by the surroundings.

it can be well understood by observing below

Now 
thermodynamical  system- It is system that can Represent in term of Thermodynamical co-ordinate

There are three thermodynamical constant 
 Pressure
Volume
Temp

Pressure can be measure by putting are applying pressure  at equilibrium
             i.e   applied pressure =  internal Pressure