Entropy is a measure of the number of specific ways in which a system can be arranged. It is considered to be the measure of disorder. In an isolated system, entropy never decreases because isolated systems spontaneously evolve towards thermodynamic equilibrium which is the state of maximum entropy.
ΔS = ∫(dQrev)/T
where entropy is found from the uniform thermodynamic temperature of a closed system divided into an incremental reversible transfer of heat into that system.
Entropy in thermodynamics is a non-conserved state function that has major importance in the science of physics and chemistry. The concept of entropy evolved in order to explain why some processes occur spontaneously while their time reversals do not. Systems tend to process in the direction of increasing entropy. Chemical reactions cause changes in entropy and entropy plays an important role in determining which direction a chemical reaction spontaneously proceeds.