Enthalpy is the ultimate state function
A full understanding of the concept of Enthalpy must be derived from the origins of its conception as well as the facile appreciation of its entire mathematical basis. Further investigation of Enthalpy, apart from the Atkins source (and not having read Gibb's original manuscripts on the topic), at Wikipedia (Enthalpy) seems to suggest that a change in Enthalpy describe the essential state of the current system relative to a state of "near-nothingness".
"In terms of thermodynamics, enthalpy can be calculated by determining the requirements for creating a system from "nothingness"; the mechanical work required, PV differs, based upon the constance of conditions present at the creation of the thermodynamic system."
The terms exothermic and endothermic are only pertinent to constant p situations, or is it? That is, are such terms soley applicable to the heat in such situations, or are they more important towards the concept of Enthalpy.
Even more interesting statements about the mysterious Enthalpy.......
"Although enthalpy is commonly used in engineering and science, it is impossible to measure directly, as enthalpy has no datum (reference point). Therefore enthalpy can only accurately be used in a closed system. However, few real world applications exist in closed isolation, and it is for this reason that two or more closed systems cannot be compared using enthalpy as a basis, although sometimes this is done erroneously."
