Task: Text Categorization
Input (English): In a Fermi fluid, this property is equivalent to Fermi energy at absolute zero, while it is identically zero for a conservative system of phonons. Diffusion may be understood as the action of its gradient, which is known as the chemical force. For each component of a system, it is defined as partial derivative of the system's free energy with respect to that component's particle number, so the equilibrium condition is that its sum over all components vanishes. FTP, name this energetic thermodynamic quantity, symbolized  and useful for deriving the law of mass action.
Output (English): Science