Task: Text Categorization
Input (English): This quantity remains constant in a Joule-Thomson process. The van't Hoff equation relates the derivative of the natural log of the equilibrium constant to the change in this quantity, and Gibbs free energy equals this quantity minus the product of temperature and entropy. The change in this quantity can be found by subtracting the (*) heats of formation of the reactants from those of the products, since the change is independent of the reaction path according to Hess's Law. For ten points, identify this thermodynamic quantity, equal to internal energy plus pressure times volume, and symbolized H.
Output (English): Science