For constant pressure, the change in this quantity equals the heat of reaction.  Also the sum of the internal energy and the pressure times volume, it's the quantity used in Hess' Law.  The variable which determines if a reac
For constant pressure, the change in this quantity equals the heat of reaction.  Also the sum of the internal energy and the pressure times volume, it's the quantity used in Hess' Law.  The variable which determines if a reaction is exo- or endothermic is, for ten points, what thermodynamic variable usually denoted by H?
For constant pressure, the change in this quantity equals the heat of reaction.  
enthalpy