what is the second law of thermodynamics?

Asked by Nimisha Menon | 15th Nov, 2010, 12:00: AM

Expert Answer:

It states that the entropy of the universe always increases in the course of every spontaneous (natural) change. Thus, combining the first and second laws of thermodynamics, the combined statement becomes: "The energy of the universe is conserved whereas the entropy of the universe always increases in any natural process".

The second law of thermodynamics introduces the concept of entropy and its relation with spontaneous processes. In an isolated system such as mixing of gases, there is no exchange of energy or matter between the system and the surroundings. But due to increase in randomness, there is increase in entropy. Thus, it can be stated that for a spontaneous process in an isolated system, the change in entropy is positive or DS > 0. However, if the system is not isolated, the entropy changes of the system and the surroundings are also to be taken into account. Then, the total entropy change (DStotal) will be equal to the sum of the change in entropy of the system (DSsystem) and the change in entropy of the surroundings (DSsurroundings).

DStotal = DSsystem + DSsurroundings

For a spontaneous process, DStotal must be positive;

DStotal = DSsystem + DSsurroundings > 0

But system and surroundings constitute universe for thermodynamic point of view so that for spontaneous change, DSuniverse > 0.

Answered by  | 16th Nov, 2010, 12:03: AM

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