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Since the pressure of the standard formation reaction is fixed at 1 bar, the standard formation enthalpy or reaction heat is a function of temperature. For tabulation purposes, standard formation enthalpies are all given at a single temperature: 298 K, represented by the symbol Δ f H ⦵ 298 K.
Numerical values of these thermodynamic properties are collected as tables or are calculated from thermodynamic datafiles. Data is expressed as temperature-dependent values for one mole of substance at the standard pressure of 101.325 kPa (1 atm), or 100 kPa (1 bar). Both of these definitions for the standard condition for pressure are in use.
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).
Std enthalpy change of formation, Δ f H o solid? kJ/mol Standard molar entropy, S o solid? J/(mol K) Heat capacity, c p? J/(mol K) 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
The definition of the Gibbs function is = + where H is the enthalpy defined by: = +. Taking differentials of each definition to find dH and dG, then using the fundamental thermodynamic relation (always true for reversible or irreversible processes): = where S is the entropy, V is volume, (minus sign due to reversibility, in which dU = 0: work other than pressure-volume may be done and is equal ...
The Van 't Hoff equation relates the change in the equilibrium constant, K eq, of a chemical reaction to the change in temperature, T, given the standard enthalpy change, Δ r H ⊖, for the process. The subscript r {\displaystyle r} means "reaction" and the superscript ⊖ {\displaystyle \ominus } means "standard".
Heat capacity, c p: 111.46 J/(mol K) [5] Liquid properties Std enthalpy change of formation, Δ f H o liquid: −277.38 kJ/mol Standard molar entropy, S o liquid: 159.9 J/(mol K) Enthalpy of combustion, Δ c H o: −1370.7 kJ/mol Heat capacity, c p: 112.4 J/(mol K) Gas properties Std enthalpy change of formation, Δ f H o gas: −235.3 kJ/mol ...
Heat capacity, c p? J/(mol K) Liquid properties 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 ...