Entropy is a fundamental concept in thermodynamics and statistical mechanics that relates to the randomness or disorder of a system. It is denoted by the symbol "S" and is measured in units of joules per kelvin (J/K) or other compatible units.
The change in entropy, denoted as ΔS, refers to the difference between the entropy of a system at two different states. It is calculated by subtracting the initial entropy (S₁) from the final entropy (S₂):
ΔS = S₂ - S₁
Entropy is considered a state function because it depends only on the current state of the system and not on the path taken to reach that state. In other words, the change in entropy between two states is independent of the specific process used to transition between them, as long as the initial and final states remain the same.
State functions, such as entropy, are convenient because they allow us to analyze and calculate thermodynamic properties without needing detailed information about the processes that occurred.