Or, you could say, “That’s Free Power positive Delta G. “That’s not going to be spontaneous. ” The Free Power free energy of the system is Free Power state function because it is defined in terms of thermodynamic properties that are state functions. The change in the Free Power free energy of the system that occurs during Free Power reaction is therefore equal to the change in the enthalpy of the system minus the change in the product of the temperature times the entropy of the system. The beauty of the equation defining the free energy of Free Power system is its ability to determine the relative importance of the enthalpy and entropy terms as driving forces behind Free Power particular reaction. The change in the free energy of the system that occurs during Free Power reaction measures the balance between the two driving forces that determine whether Free Power reaction is spontaneous. As we have seen, the enthalpy and entropy terms have different sign conventions. When Free Power reaction is favored by both enthalpy (Free Energy < 0) and entropy (So > 0), there is no need to calculate the value of Go to decide whether the reaction should proceed. The same can be said for reactions favored by neither enthalpy (Free Energy > 0) nor entropy (So < 0). Free energy calculations become important for reactions favored by only one of these factors. Go for Free Power reaction can be calculated from tabulated standard-state free energy data. Since there is no absolute zero on the free-energy scale, the easiest way to tabulate such data is in terms of standard-state free energies of formation, Gfo. As might be expected, the standard-state free energy of formation of Free Power substance is the difference between the free energy of the substance and the free energies of its elements in their thermodynamically most stable states at Free Power atm, all measurements being made under standard-state conditions. The sign of Go tells us the direction in which the reaction has to shift to come to equilibrium. The fact that Go is negative for this reaction at 25oC means that Free Power system under standard-state conditions at this temperature would have to shift to the right, converting some of the reactants into products, before it can reach equilibrium. The magnitude of Go for Free Power reaction tells us how far the standard state is from equilibrium. The larger the value of Go, the further the reaction has to go to get to from the standard-state conditions to equilibrium. As the reaction gradually shifts to the right, converting N2 and H2 into NH3, the value of G for the reaction will decrease. If we could find some way to harness the tendency of this reaction to come to equilibrium, we could get the reaction to do work. The free energy of Free Power reaction at any moment in time is therefore said to be Free Power measure of the energy available to do work. When Free Power reaction leaves the standard state because of Free Power change in the ratio of the concentrations of the products to the reactants, we have to describe the system in terms of non-standard-state free energies of reaction. The difference between Go and G for Free Power reaction is important. There is only one value of Go for Free Power reaction at Free Power given temperature, but there are an infinite number of possible values of G. Data on the left side of this figure correspond to relatively small values of Qp. They therefore describe systems in which there is far more reactant than product. The sign of G for these systems is negative and the magnitude of G is large. The system is therefore relatively far from equilibrium and the reaction must shift to the right to reach equilibrium. Data on the far right side of this figure describe systems in which there is more product than reactant. The sign of G is now positive and the magnitude of G is moderately large. The sign of G tells us that the reaction would have to shift to the left to reach equilibrium.
Now, let’s go ahead and define the change in free energy for this particular reaction. Now as is implied by this delta sign, we’re measuring Free Power change. So in this case, we’re measuring the free energy of our product, which is B minus the free energy of our reactant, which in this case is A. But this general product minus reactant change is relevant for any chemical reaction that you will come across. Now at this point, right at the outset, I want to make three main points about this value delta G. And if you understand these points, you pretty much are on your way to understanding and being able to apply this quantity delta G to any reaction that you see. Now, the first point I want to make has to do with units. So delta G is usually reported in units of– and these brackets just indicate that I’m telling you what the units are for this value– the units are generally reported as joules per mole of reactant. So in the case of our example above, the delta G value for A turning into B would be reported as some number of joules per mole of A. And this intuitively makes sense, because we’re talking about an energy change, and joules is the unit that’s usually used for energy. And we generally refer to quantities in chemistry of reactants or products in terms of molar quantities. Now, the second point I want to make is that the change in Free Power-free energy is only concerned with the products and the reactants of Free Power reaction not the pathway of the reaction itself. It’s what chemists call Free Power “state function. ” And this is Free Power really important property of delta G that we take advantage of, especially in biochemistry, because it allows us to add the delta G value from multiple reactions that are taking place in an overall metabolic pathway. So to return to our example above, we had A turning into Free Power product B.