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This is true for all enthalpies of formation. The standard enthalpy of formation is measured in units of energy per amount of substance, usually stated in kilojoule per mole (kJ mol −1), but also in kilocalorie per mole, joule per mole or kilocalorie per gram (any combination of these units conforming to the energy per mass or amount guideline).
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). Standard enthalpy of hydrogenation is defined as the enthalpy change observed when one mole of an unsaturated compound reacts with an excess of hydrogen to become fully
Enthalpy (/ ˈ ɛ n θ əl p i / ⓘ) is the sum of a thermodynamic system's internal energy and the product of its pressure and volume. [1] It is a state function in thermodynamics used in many measurements in chemical, biological, and physical systems at a constant external pressure, which is conveniently provided by the large ambient atmosphere.
Hence, the main functional application of Gibbs energy from a thermodynamic database is its change in value during the formation of a compound from the standard-state elements, or for any standard chemical reaction (ΔG° form or ΔG° rx). The SI units of Gibbs energy are the same as for enthalpy (J/mol).
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).
Std enthalpy change of formation, Δ f H o liquid –271.2 kJ/mol Standard molar entropy, S o liquid: 253.5 J/(mol K) Enthalpy of combustion, Δ c H o –2726.3 kJ/mol Heat capacity, c p: 172.0 J/(mol K) Gas properties Std enthalpy change of formation, Δ f H o gas –252.7 kJ/mol Standard molar entropy, S o gas: 342.2 J/(mol K) Heat capacity ...
The standard Gibbs free energy of formation of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of that substance from its component elements, in their standard states (the most stable form of the element at 25 °C and 100 kPa). Its symbol is Δ f G˚.
e is the elementary charge, equal to 1.6022 × 10 −19 C; ε 0 is the permittivity of free space, equal to 8.854 × 10 −12 C 2 J −1 m −1; r 0 is the nearest-neighbor distance between ions; and n is the Born exponent (a number between 5 and 12, determined experimentally by measuring the compressibility of the solid, or derived ...