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For many substances, the formation reaction may be considered as the sum of a number of simpler reactions, either real or fictitious. The enthalpy of reaction can then be analyzed by applying Hess' Law, which states that the sum of the enthalpy changes for a number of individual reaction steps equals the enthalpy change of the overall reaction.
Thermodynamic databases contain information about thermodynamic properties for substances, the most important being enthalpy, entropy, and Gibbs free energy.Numerical values of these thermodynamic properties are collected as tables or are calculated from thermodynamic datafiles.
Standard enthalpy of formation is the enthalpy change when one mole of any compound is formed from its constituent elements in their standard states. The enthalpy of formation of one mole of ethane gas refers to the reaction 2 C (graphite) + 3 H 2 (g) → C 2 H 6 (g).
The standard Gibbs free energy of formation (G f °) of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 bar of pressure and the specified temperature, usually 298.15 K or 25 °C).
In part because of its high polarity, HCl is very soluble in water (and in other polar solvents). Upon contact, H 2 O and HCl combine to form hydronium cations [H 3 O] + and chloride anions Cl − through a reversible chemical reaction: HCl + H 2 O → [H 3 O] + + Cl −. The resulting solution is called hydrochloric acid and is a strong acid.
The term bond-dissociation energy is similar to the related notion of bond-dissociation enthalpy (or bond enthalpy), which is sometimes used interchangeably.However, some authors make the distinction that the bond-dissociation energy (D 0) refers to the enthalpy change at 0 K, while the term bond-dissociation enthalpy is used for the enthalpy change at 298 K (unambiguously denoted DH° 298).
J.A. Dean (ed), Lange's Handbook of Chemistry (15th Edition), McGraw-Hill, 1999; Section 6, Thermodynamic Properties; Table 6.4, Heats of Fusion, Vaporization, and Sublimation and Specific Heat at Various Temperatures of the Elements and Inorganic Compounds
Std enthalpy of formation Δ f H o solid: −408.27 kJ/mol Standard molar entropy S o solid: 59.33 J/(mol K) Heat capacity c p: 47.99 J/(mol K) Liquid properties Std enthalpy of formation Δ f H o liquid: −390.76 kJ/mol Standard molar entropy S o liquid? J/(mol K) Heat capacity c p? J/(mol K) Gas properties Std enthalpy of formation Δ f H o ...