WHAT IS ENTROPY- Basic Of Thermodynamics

熵介绍：

熵是有用的财产，并作为工程设备第二法律分析中的有价值的工具。但熵是如此复杂的概念，我们不能给问题的充分答案 - “什么是熵”。

Not being able to describe entropy fully, however does not mean it is less useful. We could not define energy, but it did not interfere with our understanding of energy transformation and energy conservation.

Entropy can be viewed as a measure ofmolecular disorder or molecular randomness.As system becomes more disordered, the position of molecules becomes less predictable and the entropy increases. Thus entropy is lowest in solid phase and highest in gaseous phase.

From microscopic point of view, the entropy of system increase whenever the thermal randomness of system increases. Thus entropy can be defined as measure of thermal randomness or molecular disorder, which increases anytime when system goes under process.

As we know molecules of substance in solid phase continuously oscillate about their position. These oscillations decreases as temperature of substance decreases, and motion of molecules stops at absolute zero. This state represents ultimate molecular order(or minimum energy). Thereforeentropy of a pure crystalline substance at absolute zero temperature is zero由于该瞬间没有关于分子状态的疾病。该陈述被称为热力学的第三定律。

The third law of thermodynamics provides reference point for the determination of entropy. The entropy determined relative to this point is called absolute entropy. Engineers usually concerned with the changes in entropy than absolute entropy.

Entropy is non-conserved property, and there is no such thing as the conservation of entropy principle. Entropy is conserved only during idealized reversible process and increases during all actual processes.

Causes of the Increase in Entropy of the System
In actual practice the reversible isentropic process never really occurs, it is only an ideal process. In actual practice whenever there is change in the state of the system the entropy of the system increases. Here are the various causes of the increase in entropy of the closed system are:

1) Due to external interaction:In closed system the mass of the system remains constant but it can exchange the heat with surroundings. Any change in the heat content of the system leads to disturbance in the system, which tends to increase the entropy of the system.

2) Internal changes in the system:Due to internal changes in the movements of the molecules of the system there is further disturbance inside the system. This causes irreversiblities inside the system and an increase in its entropy.