Free energy change during reaction

Fig. 22.7. Thermodynamic driving forces for various anaerobic (top) and aerobic (bottom) microbial metabolisms during mixing of a subsea hydrothermal fluid with seawater, as a function of temperature. Since the driving force is the negative free energy change of reaction, metabolisms with positive drives are favored thermodynamically those with negative drives cannot proceed. The drive for sulfide oxidation is the mirror image of that for hydrogentrophic sulfate reduction, since in the calculation 02(aq) and H2(aq) are in equilibrium.

Figure 5.3 Free energy changes during a multistep reaction.

The Gibbs free energy change during a reaction is a measure of the reversible work (other than pressure-volume work) that can be obtained from the process at constant T and p. Since cellular processes are isothermal and isobaric, free energies are the quantities of choice in studying metabolic processes with respect to their ability to carry out the work of cells. 

Figure 10.36 Free energy changes during the course of a chemical reaction.

AG is the Gibbs free energy, change during the process AH is the enthalpy or the energy released or absorbed by the reaction AS is the entropy change T is the absolute temperature... 

Figure 3.1.2 Free energy changes during a reaction. The activated complex (or transition state) is the configuration of maximum free energy.

The standard reduction potentials of various biological oxidation-reduction systems allow us to predict the direction of flow of electrons from one redox couple to another under standard conditions. Furthermore, we can calculate the final equilibrium resulting when electrons flow from one redox system of known standard potential to another of known potential, as well as the free-energy changes during such reactions which will be discussed later. 

In contrast to adhesion in air, only few thermodynamic studies have been devoted to adhesion in the biological system. Recently van Oss has pointed out that i ago-cy tosis of bacteria by a phagocyte is independent of immune reactions but determined solely by the free energy change during phagocytosis ... 

Free-energy change during a spontaneous reaction (combustion of gasoiine)... 

The dissociation and adsorption and chemical reaction depend on the activation energy barrier, according to Horiuti and Polanyi [8], which is related to the free energy changes during the reaction. The correlation deduced by Evans and Polanyi [9] is given by the following expression ... 

To permit comparisons of free-energy changes during different reactions, evaluations must be made under agreed conditions, called the standard thermodynamic conditions, of a temperature of 298 K (25°C), a pressure of 1.0 atmosphere, with reactants and products at a concentration of 1.0moldm"l For the general reaction,... 

TABLE 11.2 The standard and actual free energy changes during the reactions of glycolysis... 

Gibbs-Helmholtz equation This equation relates the heats and free energy changes which occur during a chemical reaction. For a reaction carried out at constant pressure... 

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