Reaction quantity molar

CHAPTER 11 REACTIONS AND OTHER CHEMICAL PROCESSES 11.2 THE Advancement and Molar reaction Quantities... 

Equation 11.2.14 allows us to identify the molar reaction quantity as a partial derivative ... 

If a chemical process takes place at constant temperature while each reactant and product remains in its standard state of unit activity, the molar reaction quantity Af.Y is called the standard molar reaction quantity and is denoted by ArZ°. For instance, AyapH° is a standard molar enthalpy of vaporization (already discussed in Sec. 8.3.3), and ArG° is the standard molar Gibbs energy of a reaction. 

From Eq. 11.2.15, the relation between a standard molar reaction quantity and the standard molar quantities of the reactants and products at the same temperature is... 

Whereas a molar reaction quantity is usually a function of T, p, and a standard molar reaction quantity is a function only of T. This is evident because standard-state conditions imply that each reactant and product is in a separate phase of constant defined composition and constant pressure p°. 

Since the value of a standard molar reaction quantity is independent of the standard molar integral and differential quantities are identical (page 317) ... 

For this reaction, using the convention that A H°, S, and AfG° are zero for the aqueous H+ ion and the fact that AfH° and AfG° are zero for the elements, we can write the following expressions for standard molar reaction quantities ... 

An efficient way of tabulating the results of experimental measurements is in the form of standard molar enthalpies and Gibbs energies of formation. These values ean be used to generate the values of standard molar reaction quantities for reactions not investigated directly. The relations between standard molar reaction and formation quantities (Sec. 11.3.2) are... 

For examples of the evaluation of standard molar reaction quantities and standard molar formation quantities from measurements made by various experimental techniques, see Probs. 12.18-12.20,14.3, and 14.4. 

As will be shown, measurements of the cell potential of a galvanic cell are capable of yielding precise values of molar reaction quantities of the cell reaction and thermodynamic equilibrium constants, and of mean ionic activity coefficients in electrolyte solutions. 

Because G, H, and S are state functions, the thermodynamic equilibrium constant and the molar reaction quantities evaluated from Egg, g and dE°g g / dT are the same quantities as those for the reaction when it takes place in a reaction vessel instead of in a galvanic cell. However, the heats at constant T and p are not the same (page 318). During a reversible cell reaction, dS must equal dq/T, and dq/d is therefore equal to TArS° during a cell reaction taking place reversibly under standard state conditions at constant T and p. 

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