"Entropy is the measure of randomness or disorderness of the system".
The absolute value of entropy cannot be determined as it depends on the initial and final state of the system. To determine the change in entropy the change between initial and final state is considered.
In the case of an irreversible process, the change in entropy between two equilibrium states is calculated by finding a reversible path between the two states and calculating the entropy change for that path. When the products of a reaction are less complex and more disordered than the reactants, the reaction is said to proceed with a gain in entropy.
In all natural processes, the entropy of the universe increases. Living organisms consist of collections of molecules much more highly organized than the surrounding materials from which they are constructed, and organisms maintain and produce order, seemingly oblivious to the second law of thermodynamics.
Change in Entropy Formula
is given by
The thermodynamic definition of entropy is based on the change in entropy (dS) that occurs during physical or chemical changes, which is expressed as
For a measurable change between the initial and final state, this expression integrated to
The units of entropy is calories per degree or cal deg-1
. The molar entropy is expressed in joules per kelvin per mole (JK-1