. Biophysics: concepts and mechanisms. Biophysics. THE DRIVE TOWARD EQUILIBRIUM 175 THE DRIVE TOWARD EQUILIBRIUM The Driving Force It is a familiar fact that if two mechanical forces of difFerent magnitude oppose each other at a point, the resulting movement will be in the direction of the larger force. Similarly, it seems almost axiomatic that if two systems of different free energy. F, are made to oppose each other, provided they are able to interact, the interaction will proceed in the direction of the larger. For chemical reactions, if the free energies of formation for reactants and produ
. Biophysics: concepts and mechanisms. Biophysics. THE DRIVE TOWARD EQUILIBRIUM 175 THE DRIVE TOWARD EQUILIBRIUM The Driving Force It is a familiar fact that if two mechanical forces of difFerent magnitude oppose each other at a point, the resulting movement will be in the direction of the larger force. Similarly, it seems almost axiomatic that if two systems of different free energy. F, are made to oppose each other, provided they are able to interact, the interaction will proceed in the direction of the larger. For chemical reactions, if the free energies of formation for reactants and products are known, then the free energy of reaction. AF, is simply the dif- ference between the two. This value, AF, represents the maximum amount of work available from the reaction of 1 mole of reactant into product. Since AF = Ffinaj - /'„„,,,,, a negative value of AF means that the reaction will proceed spontaneously from reactants to products. Such a reaction is said to be exergonic. If (see Figure 7-3) AF is positive, free energy must be supplied from the outside—another reaction perhaps—before reactants will go into products; the reaction is said to be endergonic. The analogy with exothermic (negative AH) and endothermic (positive AH), introduced earlier, is State Figure 7-3. Free Energy of Initial and Final States. For exergonic (free energy-producing) processes, AF (= Ffin — Fin) is negative; for endergonic (free energy-consuming) processes, AF is positive. The energy-producing reactions in the living system are numerous. Nearly all the primary sources are the combustion of food products. By suitable carriers the free energy required by the endergonic syntheses of anabolism is trapped and carried through the blood stream to the locations at which the synthetic processes take place. Naturally, free energy is not a driving force, although it is often considered as such. Nor is the partial molal free energy, (dF/dn)T<P , often called. Please note that t
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