The second law of thermodynamics states that spontaneous processes always result in an overall increase in entropy of the universe. Entropy is a measure of the degree of disorder or randomness in a system. Another way to think of entropy is that it describes how spread out a system's energy is. A positive value for ΔS of a process, indicating an overall increase in entropy, results when there is a phase change from solid to liquid or gas, a phase change from liquid to gas, the dissolution of a solid into an aqueous solution, an increase in disorder within a phase, or an increase in the number of gas particles.