Entropy. What does this term mean?

Entropy is one of the functions of the state that determines the direction of the phenomena related to changes and energy flow. This concept is closely related to the second law of thermodynamics. What is this? Examples and simple explanation.

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1. What is entropy?

Entropy is a concept that comes in handy when considering changes in physical and chemical systems. According to the PWN dictionary, it is one of the state functions that determines the direction of the phenomena related to transformations and energy flow. This term was first introduced by a scientist of German origin, Rudolf Clausius.

Entropy is a measure of the degree of disorder in a system and energy dissipation. It is an extensive quantity, which means that if you want to calculate its value, you have to divide the system into small parts and then sum up their entropies, similarly to volume, mass, etc.

When explaining the concept of entropy, it is worth getting acquainted with the second law of thermodynamics. It says that if a thermodynamic system moves from one equilibrium state to another without external factors (i.e. spontaneously), its entropy will always increase.

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2. Entropy - a simple explanation

For some, the definition of entropy may be simple and understandable, while for others it may be difficult to grasp. The second group of people would be more likely to find a simple explanation based on examples. Thus, you can use examples from everyday life to assimilate this concept.

Imagine clothes arranged in a wardrobe, that is, individual garments sorted and arranged. There is a logical layout - T-shirts in one part, socks in the other, pants in another. In such an organized system, finding anything is not troublesome or time-consuming - just look into the appropriate compartment to find what you are looking for.

However, for someone else, the same wardrobe can become a mess - things not arranged according to any logical pattern, introducing disorder. Then it's hard to find what you're looking for the first time. To hit, you need to check several places.

Taking a quantity as a measure of disorder, let's call it entropy, we can say that the entropy value of a disordered system is greater than that of an ordered system. If, on the other hand, we would like to move from an ordered state to a disordered state, it will be accompanied by an increase in entropy.

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3. Examples of entropy

Any spontaneous change, whether it be a chemical reaction or a physical phenomenon, is associated with an increase in entropy. A good example would be to imagine a situation where we have a two-chamber gas container located only in the left chamber.

If we open the closed partition, the gas molecules will mix with each other in the entire container (in both chambers). This process happened spontaneously and resulted in an increase in entropy.

Is it possible for the dispersed gas molecules to return to the left ventricle on their own after some time? The answer is negative. But why? Because it will not be in accordance with the second law of thermodynamics.

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