Given the task definition and input, reply with output. In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

First proposed by Lewis, it is related logarithmically to a gas's standard Gibbs free energy divided by the temperature and gas constant. At equilibrium, this quantity must be equal in both gas and liquid phases. Taking the derivative of the natural log of this function is equates it to the derivative of a reaction's chemical potential. Equal to the gas' pressure when the gas is ideal, FTP, identify this thermodynamic quantity which replaces partial pressure when working with real gases and describes the tendency of a substance to escape from its current phase, symbolized by f.

Science