Equilibrium constant standard Gibbs energy

The most important themiodynamic property of a substance is the standard Gibbs energy of fomiation as a fimetion of temperature as this infomiation allows equilibrium constants for chemical reactions to be calculated. The standard Gibbs energy of fomiation A G° at 298.15 K can be derived from the enthalpy of fomiation AfT° at 298.15 K and the standard entropy AS° at 298.15 K from... 

Quantity K is the chemical reaction equilibrium constant for reactionyj and AG° is the corresponding standard Gibbs energy change of reaction (eq. 237). Although called a constant, fC is a function of T, but only of T. 

The derivation for equilibrium between a solution and a gaseous phase is based on the Henry law constant kiy defined on page 5. The standard Gibbs energy of the transfer of HC1 from a solution into water is... 

Perhaps the two most important outcomes of the first and the second laws of thermodynamics for chemistry are representedby equation 2.54, which relates the standard Gibbs energy (ArG°) with the equilibrium constant (K) of a chemical reaction at a given temperature, and by equation 2.55, which relates ArG° with the standard reaction enthalpy (A rH°) and the standard reaction entropy (ArA°). 

In the equilibrium state the reactants and products are in equilibrium with each other (i.e. G = 0) and the activity product given in the brackets is the equilibrium constant K. The standard Gibbs energy of the reaction (G°) is therefore... 

Calculate the equilibrium constant and the standard Gibbs energy change at 25°C for reaction 3 from the equilibrium constants obtained above for reactions 1 and 2. Show that AG° for reaction 3 = AG° of reaction 1 - AG° of reaction 2. 

The value a, being an adsorption equilibrium constant, is related to the standard Gibbs energy of adsorption, AG °, by the equation... 

Thermodynamics is used to predict whether reactants have a spontaneous tendency to change into products. This tendency is associated with a decrease in the free energy or Gibbs energy of the system (G) to a minimum. As a consequence, the thermodynamic criterion for spontaneous change at constant temperature and pressure is AG < 0. Under standard conditions (concentrations = 1 M, and P = 1 atm), the standard Gibbs energy variation (AG°) is related with the equilibrium constant (A) by equation 11 ... 

One word about the Gibbs energies of adsorption. In equilibrium the molar Gibbs energy of adsorption is zero AadGm = /P — pT 0. The reason is simple. In equilibrium and for constant P and T the chemical potential of the molecules in the gas phase n9 is equal to the chemical potential of adsorbed molecules /P. What is not zero is the standard Gibbs energy of adsorption... 

Calculate the standard Gibbs energy changes and equilibrium constants in terms of species for the following reactions at... 

Calculate the standard Gibbs energy changes and equilibrium constants in terms of species for the following reactions at 298.15 K and ionic strengths of 0, 0.10, and 0.25 M. Summarize the calculations in two tables. 

The standard Gibbs energy change, AG° (still often called standard free energy, but this term should be avoided), is related to the equilibrium constant by equation (6). 

In respect of the standard Gibbs energies, Ar G°, as defined in equations (A.l) and (A.2), in the latter case Ka refers to an equilibrium constant written in terms of (dimensionless) activities, a, (Frame 39) such that ... 

Calculation of equilibrium conversions is based on the fundamental equations of chemical-reaction equilibrium, which in application require data for the standard Gibbs energy of reaction. The basic equations are developed in Secs. 15.1 through 15.4. These provide the relationship between the standard Gibbs energy change of reaction and the equilibrium constant. Evaluation of the equilibrium constant from thermodynamic data is considered in Sec. 15.5. Application of this information to the calculation of equilibrium conversions for single reactions is taken up in Sec. 15.7. In Sec. 15.8, the phase role is reconsidered finally, multireaction equilibrium is treated in Sec. I5.9.t... 

THE STANDARD GIBBS ENERGY CHANGE AND THE EQUILIBRIUM CONSTANT... 

The calculations of the preceding example illustrate the complexity of equations that must be solved simultaneously (even for simple reactions) w the equilibrium-constant method is applied to multireaction equilibria. Mor the method does not lend itself to standardization so as to allow a general ] to be written for computer solution. The alternative method, mentioned in 15.2, is based on the fact that at equilibrium the total Gibbs energy of the s> has its minimum value. This is illustrated for a single reaction in Fig. 15.1. 

Solubility product — is the equilibrium constant Ksp of dissolution of a salt. Solubility products can be determined by direct determination of the -> concentrations of the dissolved salt, provided the activity constants are practically 1.0, or otherwise known. Solubility products can also be calculated from the standard -> Gibbs energies of formation AfG" of the species. 

If the standard Gibbs energies of formation of all the species in a reaction but one are known, say from the National Bureau of Standards Tables (4), Af G° for the species with unknown Af G/ can be calculated from an experimentally determined equilibrium constant by use of equation 3.1-14. Suffice it to say here that the Af G° values for many species of biochemical interest have been determined (5). 

The equilibrium constant for chemical reaction 6.1-3 is related to the standard Gibbs energies of formation of the five species by... 

---