Standard state Gibbs energy change

By convention, the standard-state Gibbs energy change upon reaction,, is written as... 

Together, Equation (4.545) and Equation (4.546) are equivalent to Equation (4.544). The above procedure can be extended to describe more than one independent reaction. Separate equilibrium constants, along with separate standard-state Gibbs energy changes upon reaction, are introduced for each independent reaction. 

Substitution of Equation (4.551) into Equation (4.553) yields, upon an integration by parts, the following expression for the standard-state Gibbs energy change upon reaction ... 

Standard state Gibbs energy change on reaction (kJ)... 

Most of the standard-state Gibbs energy changes as a function of temperature in Fig. 

Because, of the similarity of these equations to Eqs. 13.2-10 and 13.2-11, it is possible to construct Gibbs energy-partial pressure diagrams similar to Fig. 13.2-3. In particular, by subtracting the standard-state Gibbs energy change for the reaction... 

Compute the standard-state Gibbs energy change, enthalpy change, and entropy change for this- reaction for the temperature range in the table. 

At 452.2 K, a total pressure of 95.9 kPa, and with an appropriate catalyst, the equilibrium extent of dissociation of pure isopropanol to acetone and hydrogen is found to be 56.4 percent [H. J. Kolb and R. L. Bur-well, Jr., J. Am. Chem. Soc., 67, 1084 (1945)]. Use this information to calculate the standard-state Gibbs energy change for this reaction at this temperature. 

The reported standard-state Gibbs energy change for this reaction over a limited temperature range is... 

Consequently, if we multiply any of the half-cell reactions in Table 14.6-1 by an integer or fractional constant, the standard-state Gibbs energy change will change by that same factor, but the standard-state half-cell potential will be unchanged.,... 

The stable crystalline form of sulfur at room temperature is called rhombic sulfur, and another crystalline form is called monoclinic sulfur. The standard-state enthalpy change of formation of monoclinic sulfur at 298.15 K is 0.33 kJ mol , and the standard-state Gibbs energy change of formation of monoclinic sulfur is 0.096 kJ mol. Assume that both and AG° for the conversion of rhombic sulfur to monoclinic sulfur are tempCTature-independent. 

The quantity AG° is the standard-state Gibbs energy change for 1 mol of reaction. It applies to a reaction in which all reactants and products are in their standard states. If the standard-state Gibbs energy change is negative, the forward reaction would be spontaneous under standard conditions, and if it is positive, the reverse reaction would be spontaneous under standard conditions. 

Values of standard-state Gibbs energy changes of formation for a number of substances are included in Table A.8 of Appendix A, and larger tables are available. This table also includes values of the function —— 7fm,298 >)/7, which can also be used to calculate AG° for a reaction, as is done in Example 7.1. This function generally varies more slowly with temperature than does AfG°. If a value of AG° is needed for a temperature that is not included in the table, interpolation of this function usually gives better accuracy than does interpolation in a table of AfG values. 

The standard-state Gibbs energy change AG° depends only on temperature since the standard-state chemical potentials depend only on temperature. The value of geq is therefore equal to a constant at constant temperature. It is the equilibrium constant, denoted by K and given by the relation... 

Find the standard-state Gibbs energy change at 298.15 K for each of the reactions ... 

The standard-state Gibbs energy change for the reaction of Eq. (7.3-7) could be calculated from the Gibbs energy changes of formation of H2O, NaCl, NaOH, and HCl if the data were available. However, actual tables include data for separate ions instead of neutral electrolytes. We use the net ionic equation... 

We can calculate the thermodynamic value of K by using techniques discussed in Part 1 of this textbook. The standard-state Gibbs energy change of the reaction is 385.914 kJ mol- and the thermodynamic value of K is... 

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