In thermodynamics, the entropy of vaporization is the increase in entropy upon vaporization of a liquid. This is always positive, since the degree of disorder increases in the transition from a liquid in a relatively small volume to a vapor or gas occupying a much larger space. At standard pressure ⁠ P ⊖ ⊖ ⁠ = 1 bar, the value is denoted as ⁠ Δ Δ S vap ⊖ ⊖ ⁠ and normally expressed in joules per mole - kelvin, J/(mol·K).