Task: Text Categorization
Input (English): In the Peng-Robinson equation, the departure function for this quantity is equal to R times critical temperature times a function of the compressibility factor. The change in this quantity is divided by negative 2kt in the exponential of the expression giving the density of Schottky defects in a crystal. Both this quantity and the mass flow rate are held constant along a Fanno line. When a gas is forced through an insulated, porus plug, this quantity is held constant. For an ideal solution, the (*) change in this quantity upon solvation is zero. This quantity, which is held constant during a Joule-Thomson process, is equal to the internal energy plus pressure times volume. The fact that this quantity is a state function leads to Hess' Law. The change in this quantity determines whether a reaction is endo or exothermic. For 10 points, name this quantity symbolized H.
Output (English): Science