Free energy change for reactions

Values of AG can be used to calculate free energy changes for reactions. The relationship is entirely analogous to that given for enthalpies in Chapter 8 ... 

Free energy changes for reactions, like enthalpy or entropy changes, are additive. That is, if Reaction 3 = Reaction 1 + Reaction 2 then AG3 — AG] + A G2... 

Equation expresses an important link between two standard quantities. The equation lets us calculate standard electrical potentials from tabulated values for standard free energies. Equally important, accurate potential measurements on galvanic cells yield experimental values for standard potentials that can be used to calculate standard free energy changes for reactions. 

Free energy change for reaction HA = H + A" in kcal/mol. Standard state 1 atm., 298 K. For origin of data other than those in parentheses, see Blades et al.58 Estimated acidity value based on relationship with AG U. 

The standard free energy change for reaction 7.4.3 is given by... 

Here, we have substituted E, the standard potential for oxidation of H2, for —2FAG°, where AG° is the free energy change for reaction under standard conditions. Obviously, similar relationships can be written to calculate the equilibrium potentials for other fuels. For example, for alkanes, C, Azn z, the analogous relationship between partial pressures and the equilibrium cell potential is the following... 

Because more energy is released in reaction 2 than is consumed in reaction 1, the free-energy change for reaction 3, AG3, is negative, and the synthesis of glucose 6-phosphate can therefore occur by reaction 3. 

In Section 17.8, we calculated standard free-energy changes for reactions from the equation AG° = AH° — TAS°, using tabulated values of AH°f and S° to find AH° and AS°. Alternatively, we can calculate AG° more directly by subtracting the standard free energies of formation of all the reactants from the standard free energies of formation of all the products ... 

Be familiar with the concept of a high-energy phosphate bond, and be able to calculate the overall free energy change for reactions coupled to ATP hydrolysis. 

Related Calculations. Use this procedure to calculate heats of reaction and standard free-energy changes for reactions that involve components listed in Tables 1.17 and 1.18. 

Assumes 50% conversion factor for heat to electricity Includes the contribution of the free energy change for reaction 1... 

The fact that the reaction occurs with a decrease in volume of two to one makes the application of pressure of great benefit in driving the reaction to the right. Although no thermodynamic data are available with which to calculate free energy changes for reactions of this nature, some available data on the reaction itself show that it may be made to occur successfully. Thus by reacting the olefins and acetic acid in approximately equimolal concentrations at a total pressure of about SO atmospheres and a temperature of 150° C. over zinc chloride as a catalyst, it lias been possible to produce propyl and butyl acetates with 25 to 27 per cent conversions of acetic acid.78... 

We begin by reviewing briefly some of the qualitative models for FERs before surveying some examples of simulated FERs for proton transfer (PT) reactions. These include molecular orbital (MO)-based studies of potential energy surfaces (PES) for gas-phase reactions and valence bond (VB)-based studies of free energy changes for reactions in condensed phases. 

Since no pK values are available for hydroxyphosphoranes, the pK of pentahydroxyphosphorane is estimated by the method of Branch and Calvin (1941) as 8.5. The application of the free-energy change for reaction (4) to... 

The principle of microscopic reversibility allows one to express the backward rate constant in terms of the forward rate constant divided by Kp, which is the equilibrium constant based on gas-phase partial pressures. Kp has units of pressure to the power 5, where 5 is the sum of the stoichiometric coefficients (i.e., 8 = —2 for this problem). Handbook values for standard-state free energies of formation at 298 K are used to calculate the Gibbs free-energy change for reaction at 298 K (i.e., 29s) thi to calculate a dimensionless... 

Using example values for AH and AS we can calculate the Gibbs free energy change for reactions at different temperatures (lOK and 10000 K) for positive and negative values of AH and AS. 

The Gibbs free energy change for reactions (10.1)-(10.4) will be negative if the potentials for the cathodic reactions (10.6)-(10.9) respectively are more positive than for the anodic reaction (10.5). Hence, corrosion is possible at pH values where the dotted lines for oxygen reduction (reactions (10.7) and (10.39)) or hydrogen evolution (reactions (10.9) and (10.38)) lie above the line for the M/M couple. 

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