PPT Slide
- In classical thermodynamics the entropy is defined by:
- the ? entropy can be related to S as: we call S the “conventional” entropy
Entropy increase on heat flow
The total entropy change of the system when we remove a positive amount of energy ?U from system 1 and the same amount to system 2:
When ?1> ?2 dS is positive, otherwise negative
Law of increase of entropy
The total entropy always increases when two systems are brought into thermal contact!
Let U10 and U20 be the initial internal energy of system 1 and 2 respectively, and let U=U10+U20 be the total energy. We can write than:
Here stands for the energy of system 1 in the most probable configuration when it is in thermal contact with system 2. For the entropy we get:
The evolution of the combined system towards the final thermal configuration is realized through intermediate configurations with intermediate energies and entropy.
Law of increase of entropy