The standard reaction Gibbs energy

The standard reaction Gibbs energy is centrai to the discussion of chemical equilibria and the calculation of equilibrium constants. It is also a useful indicator of the energy available from catabolism to drive anabolic processes, such as the synthesis of proteins. 

We have seen that standard reaction Gibbs energy, AjG, is defined as the difference in standard molar Gibbs energies of the products and the reactants weighted by the stoichiometric coefficients, v, in the chemical equation 

For example, the standard reaction Gibbs energy for reaction A is the difference between the molar Gibbs energies of fructose-6-phosphate and glucose-6-phosphate in solution at 1 mol dm and 1 bar. 

We cannot calculate AjG from the standard molar Gibbs energies themselves because these quantities are not known. One practical approach is to calculate the standard reaction enthalpy from standard enthalpies of formation (Section 1.11), the standard reaction entropy from Third-Law entropies (Section 2.5), and then to combine the two quantities by using 

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K is the thermodynamic equilibrium constant which is only dependent on T, and ArG° is the standard reaction Gibbs energy of the reaction, which can be calculated with... 

The concentrations in Q have arbitrary values. Note that the standard reaction Gibbs energy is given by... 

The thermodynamic data in the selected set refer to a temperature of 298.15 K (25.00°C), but they can be recalculated to other temperatures if the corresponding data (enthalpies, entropies, heat capacities) are available [97PU1/RAR]. For example, the temperature dependence of the standard reaction Gibbs energy as a function of the standard reaction entropy at the reference temperature (7o= 298.15 K), and of the heat capacity function is ... 

AG° is the standard reaction Gibbs energy. Then, combining the logarithmic terms. 

The standard reaction Gibbs energy for the hydrolysis of ATP is+10 kj moT at 298 K. What is the biological standard state value ... 

Example 4.4 ) Calculating the standard reaction Gibbs energy of an enzyme-catalyzed reaction... 

Evaluate the standard reaction Gibbs energy at 25°C for the reaction C02(g) + H20(1) —> H2C03(aq) catalyzed by the enzyme carbonic anhydrase in red blood cells. 

Self-test 4.6 ) Use the information in the Resource section to determine the standard reaction Gibbs energy for 3 Ojfg) -> 2 03(g) from standard enthalpies of formation and standard entropies. 

To determine the standard reaction Gibbs energy for the complete oxidation of solid sucrose, C,2H220n(s), by oxygen gas to carbon dioxide gas and liquid water,... 

O 3. The standard reaction Gibbs energy is the difference of the standard Gibbs energies of formation of the products and reactants weighted by the stoichiometric coefficients in the chemical equation. 

The equihbrium constant for the hydrolysis of the dipeptide alanylglycine by a peptidase enzyme is fC=8.1 x 10 at 310 K. Calculate the standard reaction Gibbs energy for the hydrolysis. 

One enzyme-catalyzed reaction in a biochemical cyde has an equihbrium constant that is 10 times the equihbrium constant of a second reaction. If the standard Gibbs energy of the former reaction is -300 kJ mol , what is the standard reaction Gibbs energy of the second reaction ... 

The standard reaction Gibbs energies (at pH = 7) for the hydrolysis ofglucose-l-phosphate, glucose-6-phosphate, and glucose-3-phosphate are -21, -14, and -9.2 kJ mol , respectively. Calculate the equihbrium constants for the hydrolyses at 37°C. 

In this expression, A,G is the standard reaction Gibbs energy and Q is the reaction quotient for the cell reaction. When we substitute this relation into eqn 5.12 written as ceii = -Afi/vF, we obtain the Nernst equation ... 

To discuss the thermodynamics of bioiogicai processes, we need to be abie to predict the standard reaction Gibbs energies of bioiogicai eiectron transfer reactions and their variation with pH. 

The relation between the standard cell potential and the standard reaction Gibbs energy is a convenient route for the calculation of the standard potential of a couple from two other standard potentials. We make use of the fact that G is a state function and that the Gibbs energy of an overall reaction is the sum of the Gibbs energies of the reactions into which it can be divided. In general, we cannot combine the E values directly because they depend on the value of v, which may be different for the two couples. 

The standard reaction enthalpy from the standard reaction Gibbs energy and entropy... 

It is more useful, especially for biological reactions in aqueous environments, to express the Eyring equation in terms of thermodynamic parameters and to discuss reactions in terms of their empirical values. Thus, we saw in Section 4.3 that an equilibrium constant may be expressed in terms of the standard reaction Gibbs energy —RTlnK = We do the same here, and express K in terms of the... 

The standard reaction Gibbs energy, A G, with electron transfer becoming more efficient as A G becomes more negative. For example, kinetically efficient oxidation of D requires that its standard reduction potential be lower than the standard reduction potential of A. 

Many of the key features of Marcus theory have been tested by experiments, showing in particular the predicted dependence of on the standard reaction Gibbs energy and the edge-to-edge distance between electron donor and acceptor. 

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