Entropy is an essential concept in the fields of physics and chemistry, and it also has applications in a variety of other fields, such as cosmology, biology, and economics. It is a subfield of thermodynamics in the field of physics. It is considered a subfield of physical chemistry within the field of chemistry.

Entropy can be defined in a straightforward manner by stating that it is the measure of the disorder that exists within a system. The entropy of an ordered system is lower than that of a disordered system, which has a higher entropy. The term “entropy” is frequently defined in a slightly different manner by physicists, who assert that it refers to the energy of a closed system that cannot be used to perform work.

Because entropy is a comprehensive property of a thermodynamic system, its value is directly proportional to the total mass of the constituent substances. In equations, the letter S is used to represent entropy as a symbol. It is measured in joules per kelvin (J.K-1) or kg⋅m2⋅s−2⋅K−1.