What is entropy? How is it related to the second law?

Entropy is simply a way to measure quantitatively what the second law of thermodynamics describes: the dispersal of energy in a process in our material world. Entropy is not a complicated concept qualitatively.

Most certainly, entropy is not disorder nor a measure of chaos — even though it is thus erroneously defined in dictionaries or pre-2006 sources.

Because entropy is an index of the second law's predictions about energy, the short word entropy is often used interchangeably for the cumbersome phrase, "the second law of thermodynamics". A concise summary of entropy's nature is: Entropy change measures the dispersal of energy: how much energy is spread out in a particular process, or how widely spread out it becomes (at a specific temperature).
You see now how hot pans cooling and chemical reactions belong to the ‘how much' catergory where energy is being transferred.
Coffee in cream and gas expansion and perfume in air are ‘how widely' processes where the initial energy of the molecules stay the same but the volume occupied by the molecules increases.
Energy's dispersal can be easily seen by anyone in thousands of common occurrences like the few we have talked about because the second law isn't some exotic or abstract mathematical theory.
The second law is really just a summary of ordinary human experience. The details of how energy disperses in such everyday practical events can be elegantly correlated with the probable behavior of atoms and molecules.


may the force be with you