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The formation reaction is defined as formation of the specified compound from its constituent elements in their standard states. A generalized reaction can be written for all possible formation reactions that can be evaluated with TDE.
CaHbOcNdSeFfClgBrhIi → aC(graphite) + 0.5bH2(g) + 0.5cO2(g) + 0.5dN2(g) + 0.5eS(II) + 0.5fF2(g) + 0.5gCl2(g) + 0.5hBr2(l) + 0.5iI2(c)
Enthalpy of Formation Δhf° for the stable phase at T = 298.15 K The enthalpy of formation for the stable phase at T = 298.15 K (p = 101.325 kPa) is evaluated as a pure-compound property.
The enthalpy of formation in the condensed states (crystal & liquid) are typically evaluated from enthalpies of combustion determined by combustion-bomb calorimetry. See Cox and Pilcher, 1970  for details of this method. Conversion of enthalpies of combustion to enthalpies of formation requires use of some key values, such as the enthalpy of formation at T = 298.15 K and p = 101.325 kPa for water. These values are are taken from the following literature sources:
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