Entropy is a measure of the disorder or randomness of a system/19%3A_Chemical_Thermodynamics/19.02%3A_Entropy_and_the_Second_Law_of_Thermodynamics). It is a state function that describes how much energy is not available to do work. Entropy can be thought of as a measure of the dispersal of energy, and it measures how much energy has been dispersed in a process. The flow of any energy is always from high to low, so entropy always tends to increase. Entropy is related not only to the unavailability of energy to do work, but it is also a measure of disorder.
Entropy can be defined in several ways and can be applied in various fields such as physics, chemistry, biology, sociology, weather science, and climate change. In thermodynamics, entropy is used to describe the behavior of a system in terms of thermodynamic properties such as temperature, pressure, entropy, and heat capacity. Entropy is also a measure of the amount of disorder in a physical or biological system.
Entropy can increase or decrease depending on the changes in the system. Chemical and physical changes in a system may be accompanied by either an increase or a decrease in the disorder of the system, corresponding to an increase in entropy or a decrease in entropy, respectively/19%3A_Chemical_Thermodynamics/19.02%3A_Entropy_and_the_Second_Law_of_Thermodynamics). The change in entropy is defined as the difference between the entropies of the final and initial states/19%3A_Chemical_Thermodynamics/19.02%3A_Entropy_and_the_Second_Law_of_Thermodynamics). A reversible process is one for which all intermediate states between extremes are equilibrium states, and the entropy change for a reversible process is given by the equation ΔS = qrev/T, where qrev is the heat absorbed or released in a reversible process and T is the temperature at which the process occurs/19%3A_Chemical_Thermodynamics/19.02%3A_Entropy_and_the_Second_Law_of_Thermodynamics).
