One process in which this quantity is constant is called a throttling process.
One process in which this quantity is constant is called a throttling process. The natural variables of this potential are pressure and entropy. Two terms must be added to the Helmholtz free energy to derive this potential. The statement that this quantity is a state function and hence can be computed using a Born-Haber cycle is known as Hess's law. Since most chemical reactions aren't conducted at constant volume, this potential is more useful than the internal energy for determining whether a reaction is exothermic. For 10 points, name this quantity typically denoted "H" that measures the heat content of a system. 
One process in which this quantity is constant is called a throttling process.
enthalpy [accept lattice enthalpy; prompt on "lattice energy"; prompt on "energy"; prompt on "heat"; prompt on "H"] 