ENTROPY

Entropy

Entropy represents the energy in the system which couldn't be utilised due to some deficiency of the system. As we know that when we burn oil, only part of heat energy is utilised and rest goes un-utilised. This resents that efficiency of system is not equal to input of heat energy into Heat-Engine and it is always less than heat input. This is as brought out in 2nd Law of Thermodynamics.

Whether it is a case of Heat Input (heat engine) or Heat extraction (Refrigeration), the system output will be < total input. The most ideal case for thermodynamic cycle is Carnot-Cycle. It is defined as follows:

"Entropy" is defined as a measure of unusable energy within a closed or isolated system (the universe for example). As usable energy decreases and unusable energy increases, "entropy" increases.

Entropy is also a gauge of randomness or chaos within a closed system. As usable energy is irretrievably lost, disorganization, randomness and chaos increase.

For more details refer my scanned hand notes.