Standard molar Gibbs free energy formation

To find a numerical value for AHi, we need to know ArH° at one temperature, while evaluation of I requires ArG° at one temperature. The usual choice is to obtain ArH° and ArG° at T = 298.15 K from standard molar enthalpies of formation and standard molar Gibbs free energies of formation. Earlier in this chapter we referred to examples of these quantities. It is now time to define AfH° and AfG° explicitly and describe methods for their measurement. 

Standard molar enthalpies of formation, AfH°m, and standard molar Gibbs free energies of formation, Af(7, are useful, since they can be used to calculate ArH° and ArG°. The relationships are... 

COM/PRA] Comert, H., Pratt, J. N., The standard molar Gibbs free energy of formation of NiO from high-temperature e.m.f. measurements, J. Chem. Thermodyn., 16, (1984), 1145-1148. Cited on pages 105, 401. 

Determination of the standard molar Gibbs free energies of formation of the silicates of cobalt and nickel by solid-state galvanic cells involving the CaF2-based composite electrolyte, J. Chem. Thermodyn., 32, (2000), 931-935. Cited on pages 243, 244,437. 

The standard molar Gibbs free energy of formation is... 

The symbol for standard molar Gibbs free energy of formation is AG . The units are kj mol ... 

In books of tables, usually the standard values of molar Gibbs free energies of formation A f G of substances are listed. A f G is the change of Gibbs free energy that accompanies the formation of 1 mol of the substance in question, pure or dissolved, from its elements under standard conditions. Because AfG is nothing else than a special case of ArG, it corresponds to the negative drive of formation (— Ji) or the positive drive of decomposition J , respectively. In Sect. 4.6, however. 

Calculate the standard Gibbs free energy of formation of HI(g) at 25°C from its standard molar entropy and standard enthalpy of formation. 

What Do We Need to Know Already The concepts of chemical equilibrium are related to those of physical equilibrium (Sections 8.1-8.3). Because chemical equilibrium depends on the thermodynamics of chemical reactions, we need to know about the Gibbs free energy of reaction (Section 7.13) and standard enthalpies of formation (Section 6.18). Ghemical equilibrium calculations require a thorough knowledge of molar concentration (Section G), reaction stoichiometry (Section L), and the gas laws (Ghapter 4). 

Calculate changes in Gibbs free energy, AG, (a) from values of AH and AS and (b) from tabulated values of standard molar free energies of formation know when to use each type of calculation... 

Gibbs free-energy change when 1 mole of a compound is synthesized from its elements in their standard states. (8.4) standard melting point. The melting point of a substance at 1 bar pressure. (5.2) standard molar enthalpy of formation (Aff J). The enthalpy change that results when 1 mole of a compound in its standard state is formed from its elements in their standard states. 

Appendix V. Some molar standard Gibbs free energies of formation (AGf), molar standard enthalpies (or heats) of formation (AH() and molar absolute entropies (S ) at 25°C and I atmosphere"... 

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