What Are Some Examples of Entropy?

Entropy is seen in situations that involve the dispersal of energy from a concentrated state to a less concentrated one, such as a hot pan cooling down, a tire blowing and releasing its air, the rusting of metal or cream mixing with coffee in a mug. These examples follow the definition of entropy, which is a measure of how energy and matter are dispersed within a system.

According to the second law of thermodynamics, energy between a system and its surroundings spreads out towards equilibrium if unobstructed from doing so; entropy changes are determined by how the amount of energy is dispersed and spread. When matter spreads to a greater volume, such as the cream in the coffee cup, the energy content also spreads and increases entropy.

Entropy is not a measure of disorder. The rusting of metal, for example, involves an increase in entropy because iron and oxygen change to a lower energy state, iron oxide, but without any disorder introduced. Systems in an ordered state can contain more energy than their disordered state, so the system becomes disordered as a byproduct of the energy spreading out to reach equilibrium. However, if a neat room is taken as a system and the room is trashed to create disorder, the amount of energy contained in the room is not changed or spread with its surroundings, thus entropy is not changed.