1. Statistical Interpretation of Entropy
By:-
Rama Arora Associate Professor
Govt. College for Girls
Sector 11, Chandigarh

2. Statistical Definition of Entropy
Statistically the Entropy S of a system is the product of the natural logarithm of thermodynamics probability W and Boltzmann Constant k
S = k lnW
(k = 1.38 x erg/K)
So Entropy in the state of equilibrium of system is given by
S = K ln (Wmax)

3. Change of entropy of a system
The thermodynamic probability W is a function of no. of particles (n) (which is function of µ amount of substance, the total no. of available phase space cells (which in turn depends upon the volume) and the energy u of the system.
S = f (u, v, µ)
Therefore entropy s, is also a function of µ, v, u. So the entropy of the system can be changed by changing the energy µ.

4. First law of thermodynamics
From first law of thermodynamics
δQ = dU + PdV
Since V is constant, so
δQ = dU
Since δQ is infinitesimally small so the system is assumed to be in most probable state
ds = δQ /T

5. Additive Nature of Entropy
S1 and S2 be entropies of the sub-systems A and B respectively.
S = S1 + S2
In general, the entropy of the system is given by the summation of entropies of all the subsystems of the system.
i.e. S = ∑ Si A B k
i=1

6. Third law of thermodynamics
Thermodynamics probability W decreases with the decrease of temp.
The minimum possible temperature is called the absolute zero.
S = k log W
When W = 1, S=0.
The absolute zero temperature is 00 kelvin

7. Reversible Process -> Carnot cycle
A process in which a system can be retraced to its initial state by reversing the controlling factor is called reversible process.
-> Carnot cycle

8. Irreversible Process Equilibrium Only At End of Process
Physical Processes That Proceed in One Direction But Not The Other
Tends Towards Equilibrium
Equilibrium Only At End of Process
->Thermal Conduction
Hot
Cold dQ

9. Irreversible Processes
Diffusion of gases

10. Principle of increase of entropy
A natural process always takes place in such a direction as to cause an increase in the entropy of the system and surroundings.
In an isolated system the entropy of the system always tends to increase.

11. Ice melting -an example of "entropy increasing"

12. Entropy and Disorder Entropy is a measure of molecular disorder.
It is the law of the nature that disorder is more probable than order.

13. Is this your room/
Then you already know about entropy

14. A system (such as a room) is in a state of
high entropy when its degree of disorder is
high.
As the order within a system increases,
its entropy decreases.

15. Thanx !