Free energy change and the equilibrium constant

It is only under standard conditions (1 atm and 25°C) that A is sufficient to determine whether a reaction is spontaneous or not. We will now derive a relation for the molar free energy change AG under any conditions in terms of AG and the equilibrium constant for the chemical reaction. 

Equation (2.43) can be used to obtain the value of AG , which is the change in the Gibbs free energy for a reaction at 1 atm and temperature r, from the equilibrium constant for the reactant at pressure p and temperature T. For standard conditions (1 atm and 25.00°C), Eq. (2.43) becomes 

We can see from Eq. (2.43) that if AG has a large negative value, will be large and positive, which implies from Eqs. (1.6) and (1.9a) that at equilibrium the products will be present in high concentrations. Conversely, if AG is positive then A p l, and at equilibrium the reactants will be favored over the products. 

Are the reactants or products favored for the forward reaction at equilibrium  

Since is so large, the products of the forward reaction are certainly favored under equilibrium conditions at a temperature of 25°C and 1 atm. 

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One of the most important characteristics of a cell is its voltage, which is a measure of reaction spontaneity. Cell voltages depend on the nature of the half-reactions occurring at the electrodes (Section 18.2) and on the concentrations of species involved (Section 18.4). From the voltage measured at standard concentrations, it is possible to calculate the standard free energy change and the equilibrium constant (Section 18.3) of the reaction involved. 

The Van t Hoff isotherm establishes the relationship between the standard free energy change and the equilibrium constant. It is of interest to know how the equilibrium constant of a reaction varies with temperature. The Varft Hoff isochore allows one to calculate the effect of temperature on the equilibrium constant. It can be readily obtained by combining the Gibbs-Helmholtz equation with the Varft Hoffisotherm. The relationship that is obtained is... 

The two thermodynamic equations that are most useful for simple kinetic and binding experiments are (1) the relationship between the Gibbs free energy change and the equilibrium constant of a reaction. 

Relationship Between the Standard Free-Energy Change and the Equilibrium Constant for a Reaction AG° = -RT In K... 

Calculate the standard free-energy change and the equilibrium constant of (17-30). 

By applying these concepts to chemical equilibria we can derive (see Box 3.2) the following simple relationship between free energy change and the equilibrium constant of a reversible reaction, K ... 

See also Free Energy and Useful Work, Free Energy and Concentration, Free Energy Change and the Equilibrium Constant... 

Table 3.7 lists the Gibbs free energy of formation of these four chemicals. Tables 3.8 and 3.9 list the molar Gibbs free energy changes and the equilibrium constants of Reactions 3.9,3.11,3.12, and 3.13, respectively. 

The Standard Free Energy Change and the Equilibrium Constant... 

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