Enthalpy of Formation

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.

C_aH_bO_cN_dS_eF_fCl_gBr_hI_i → aC_(graphite) + 0.5bH_2(g) + 0.5cO_2(g) + 0.5dN_2(g) + 0.5eS_(II) + 0.5fF_2(g) + 0.5gCl_2(g) + 0.5hBr_2(l) + 0.5iI_2(c)

Enthalpy of Formation Δh_f° 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 [42] 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:

Compound	State	Citation
CO2	g	[43]
H2O	l	[43]
HF	aq	[44]
HCl	aq	[45]
HBr	aq	[45]
H2SO4	aq	[45]