A property that is the same for any two systems that are in thermodynamic equilibrium with each other. Compare with exothermic . A process that absorbs heat. The enthalpy change for an endothermic process has a positive sign. Compare with heat and work .
Energy is an abstract property associated with the capacity to do work .
Compare with heat . While changes in enthalpy can be measured using calorimetry, absolute values of enthalpy usually cannot be determined. The change in enthalpy that occurs when one mole of a compound is converted into gaseous atoms. All bonds in the compound are broken in atomization and none are formed, so enthalpies of atomization are always positive. The change in enthalpy when one mole of compound is completely combusted.