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The standard state of a material (pure substance, mixture or solution) is a reference point used to calculate its properties under different conditions.A degree sign (°) or a superscript Plimsoll symbol (⦵) is used to designate a thermodynamic quantity in the standard state, such as change in enthalpy (ΔH°), change in entropy (ΔS°), or change in Gibbs free energy (ΔG°).
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.
It is therefore the change in these functions that is of most interest. The isobaric change in enthalpy H above the common reference temperature of 298.15 K (25 °C) is called the high temperature heat content, the sensible heat, or the relative high-temperature enthalpy, and called henceforth the heat content.
Standard enthalpy of combustion is the enthalpy change when one mole of an organic compound reacts with molecular oxygen (O 2) to form carbon dioxide and liquid water. 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).
Liquid properties Std enthalpy change of formation, Δ f H o liquid: −80.882 ± 0.053 kJ/mol [2] Standard molar entropy, S o liquid? J/(mol K) Heat capacity, c p: 80.80 J/(mol K) Gas properties Std enthalpy change of formation, Δ f H o gas: −45.556 ± 0.029 kJ/mol [3] Std Gibbs free energy change of formation, Δ f G o gas: −16.6 kJ/mol ...
Liquid properties Std enthalpy change of formation, Δ f H o liquid: −238.4 kJ/mol Standard molar entropy, S o liquid: 127.2 J/(mol K) Enthalpy of combustion Δ c H o: −715.0 kJ/mol Heat capacity, c p: 70.8–90.5 J/(mol K) (at −97.6 to 64.7 °C) [5] 79.9 J/(mol K) at 20 °C Gas properties Std enthalpy change of formation, Δ f H o gas ...
Liquid properties Std enthalpy change of formation, Δ f H o liquid: −118.910 kJ/mol Standard molar entropy, S o liquid: 171.0 J/(mol K) Heat capacity, c p: 98.36 J/(mol K) Gas properties Std enthalpy change of formation, Δ f H o gas: −104.7 kJ/mol Standard molar entropy, S o gas: 269.91 J/(mol K) Enthalpy of combustion, Δ c H o: −2220. ...
Liquid properties Std enthalpy change of formation, Δ f H o liquid-147.6 kJ/mol Standard molar entropy, S o liquid: 229.7 J/(mol K) Heat capacity, c p: 132.42 J/(mol K) –262 °C to –3 °C Gas properties Std enthalpy change of formation, Δ f H o gas –124.7 kJ/mol Standard molar entropy, S o gas: 310.23 J/(mol K) Enthalpy of combustion ...