What does the second law of thermodynamics state?

The second law of thermodynamics states that the entropy of an isolated system always increases over time. Entropy is a measure of disorder or randomness in a system, and this law implies that natural processes tend to move toward a state of increased disorder. In practical terms, this means that energy transformations are not 100% efficient, and some energy is always lost as heat or increases the overall entropy of the universe.

This law has profound implications in various fields, including physics, chemistry, and even information theory. It explains why certain processes are irreversible, such as the melting of ice or the mixing of substances. It also underlines the directionality of thermodynamic processes, telling us that while systems can reach equilibrium, they will inherently trend towards more disordered states rather than less.

Energy conservation and creation in reactions are addressed by the first law of thermodynamics, which focuses on the conservation aspect and does not relate to entropy. While all systems may eventually reach thermal equilibrium, this is a concept tied more closely to temperature uniformity than to the core principle of the second law regarding entropy. Therefore, the assertion that the entropy of an isolated system always increases captures the essence of the second law accurately.