# What Entropy indicates?

/ Thursday, 20 July 2017 / Published in Technical Corner

Second law of thermodynamics leads to the birth of a new property i.e. entropy which is an abstract property. Entropy is a very useful property, we all know but why the word entropy is not used in daily life like other properties (Energy, temperature and pressure). Answer of this question is that we don’t understand the entropy completely. We have formulae for entropy change for different processes. So we only use these formulae to solve our problem and don’t try to understand the meaning of entropy. So our discussion will be focused on the physical meaning of entropy.

By considering the microscopic nature of matter, Entropy can be viewed as a measure of molecular disorder, or molecular randomness. As a system becomes more disordered, the positions of the molecules become less predictable and the entropy increases. Thus, it is not surprising that the entropy of a substance is lowest in the solid phase and highest in the gas phase (Fig. 1). In the solid phase, the molecules of a substance continually oscillate about their equilibrium positions, but they cannot move relative to each other, and their position at any instant can be predicted with good certainty. In the gas phase, however, the molecules move about at random, collide with
each other, and change direction, making it extremely difficult to predict accurately the microscopic state of a
system at any instant. Associated with this molecular chaos is a high value of entropy.

#### Entropy in daily life

Entropy means disorder or disorganization in a system. The use of the word “Entropy” is not limited to thermodynamics. Rather, it occupies large space. For example, efficient people lead low-entropy (highly organized)
lives. They have a place for everything (minimum uncertainty), and it takes minimum energy for them to locate something. Inefficient people, on the other hand, are disorganized and lead high-entropy lives. They take hours to find something they need. Now, consider two identical buildings, each containing one million books. In the first
building, the books are piled on top of each other, whereas in the second building they are highly organized, shelved, and indexed for easy reference. There is no doubt about which building a student will prefer to go to for
checking out a certain book. Yet, some may argue from the first-law point of view that these two buildings are equivalent since the mass and knowledge content of the two buildings are identical, despite the high level of disorganization (entropy) in the first building. This example illustrates that any realistic comparisons should involve the second-law point of view.

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