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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.
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).
For example, the standard enthalpy of combustion of ethane gas refers to the reaction C 2 H 6 (g) + (7/2) O 2 (g) → 2 CO 2 (g) + 3 H 2 O (l). Standard enthalpy of formation is the enthalpy change when one mole of any compound is formed
Std enthalpy change of vaporization, Δ vap H o? kJ/mol Std entropy change of vaporization, Δ vap S o? J/(mol·K) Solid properties Std enthalpy change of formation, Δ f H o solid-985.2 kJ/mol [4] Standard molar entropy, S o solid: 83.4 J/(mol K) [4] Heat capacity, c p: 87.5 J/(mol K) [4] Liquid properties Std enthalpy change of formation, Δ ...
The formation of O 2 occurs in the gas phase via the neutral exchange reaction between • O and • HO, which is also the main sink for • HO in dense regions. [ 20 ] We can see that atomic oxygen takes part both in the production and destruction of • HO, so the abundance of • HO depends mainly on the H + 3 abundance.
Al(OH) 3 is built up of double layers of hydroxyl groups with aluminium ions occupying two-thirds of the octahedral holes between the two layers. [ 5 ] [ 6 ] Four polymorphs are recognized. [ 7 ] All feature layers of octahedral aluminium hydroxide units, with hydrogen bonds between the layers.
Benson group-increment theory (BGIT), group-increment theory, or Benson group additivity uses the experimentally calculated heat of formation for individual groups of atoms to calculate the entire heat of formation for a molecule under investigation. This can be a quick and convenient way to determine theoretical heats of formation without ...
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