Importance of Entropy

The maximum possible efficiency obtainable by any engine working on a reversible Carnot Cycle is given by

                                                                      n = T1-T2/T1

where

                                                                      T1 = Highest absolute temperature, and 

                                                                      T2 = Lowest absolute temperature.

in general, efficiency is given by

                                                     n = Maximum work obtained/Heat supplied or absorbed = &W/&Q

For one degree temperature drop, the above expression may be written as

                                                               &W = $Q/T = dS = Change in entropy 

From This expression, it can be easily understand that

1. The change in entropy represents the maximum amount of work obtainable per degree drop in temperature.

2. The change in entropy may be regarded as a measure of the rate the availability of heat for transformation into work.

3. The increase in entropy is obtained from a given quantity of heat at a low temperature.