According to the Clausius equality, for a reversible cyclic thermodynamic process: ∮ ∮ δ δ Q r e v T = 0 which means the line integral ∫ ∫ L δ δ Q r e v / T is path-independent. Thus we can define a state function S , called entropy : d S = δ δ Q r e v T Therefore thermodynamic entropy has the dimension of energy divided by temperature, and the unit joule per kelvin (J/K) in the International System of Units (SI).