Equilibrium constant calculations

Thermodynamic equilibrium constant calculated as in Example 7.15 KO = Exp(-DeltaGRO/Rg/TO)... 

For a strong acid, the H, 0 concentration can be determined directly from the concentration of the acid. For a weak acid, the H, 0 1 concentration must be determined first from an equilibrium constant calculation (Sec. 20.3) then the pH is calculated. 

Equilibrium constants calculated from the composition of saturated solutions are dependent on the accuracy of the thermodynamic model for the aqueous solution. The thermodynamics of single salt solutions of KC1 or KBr are very well known and have been modeled using the virial approach of Pitzer (13-15). The thermodynamics of aqueous mixtures of KC1 and KBr have also been well studied (16-17) and may be reliably modeled using the Pitzer equations. The Pitzer equations used here to calculate the solid phase equilibrium constants from the compositions of saturated aqueous solutions are given elsewhere (13-15, 18, 19). The Pitzer model parameters applicable to KCl-KBr-l O solutions are summarized in Table II. 

It is easily shown that equation 2.65 is a fair approximation only if the ideal solution model is valid and A, B, and C are in very low concentrations. By accepting unity activity coefficients for all the species, equation 2.63 leads one to the equilibrium constant calculated from the molalities (Km) ... 

In Chapter 4 we will learn to calculate the equilibrium constant for an exchange reaction like Equation2.15 using the Born-Oppenheimer approximation. If, in addition, the adiabatic correction is included, the equilibrium constant calculated in the Born-Oppenheimer approximation must be multiplied by a correction factor containing the energy difference AAC. 

GASEQ A Chemical Equilibrium Program for Windows. GASEQ is a PC-based equilibrium program written by C. Morley that can solve several different types of problems including composition at a defined temperature and pressure, adiabatic temperature and composition at constant pressure, composition at a defined temperature and at constant volume, adiabatic temperature and composition at constant volume, adiabatic compression and expansion, equilibrium constant calculations, and shock calculations. More information can found at the website http //www.arcl02.dsl.pipex.com/gseqmain.htm. 

Free energy changes and equilibrium constants calculated from the enthalpy and entropy values estimated by the group-contribution method generally are reliable only to the order of magnitude. For example, Andersen et al. [1] have found that their estimated enthalpies and entropies usually differ from experimental values [7]... 

From the following equilibrium constants, calculate the equilibrium constant for the reaction H02CC02H 2H+ + C20 . 

Figure 15.2 Graph of log K, the thermodynamic equilibrium constant calculated from molecular data (solid line), against 1 /T. Also shown is a prediction of log K obtained by Nernst (dashed-dotted line).

Reaction (15.1) is known as the Haber reaction in recognition of the major role of Fritz Haberf in characterizing this process early in the twentieth century. At that time neither the molecular data nor the mathematical relationships were available for calculating the equilibrium condition, so that Haber had to rely upon experimental measurement. He determined the equilibrium concentration of NH3 in the (N2 + 3H2) mixture8 as a function of temperature. His measurements, graphed as mole percent NH3, were made at a total pressure of 1 atm (1.01 bar), and are also shown in Figure 15.3.1 The agreement with the prediction from the thermodynamic equilibrium constant calculated from the molecular parameters (solid line) is excellent. 

Having the K equilibrium constants calculated for each component of the mixture, the FlshRef program applies the equation shown on code line 1010 ... 

Calculation of AG ° from an Equilibrium Constant Calculate the standard free-energy change for each of the following metabolically important enzyme-catalyzed reactions, using the equilibrium constants given for the reactions at 25 °C and pH 7.0. 

In molecular reaction schemes, only stable molecular reactants and products appear short-lived intermediates, such as free radicals, are not mentioned. Nearly all the reactions written are considered as pseudo-elementary processes, so that the reaction orders are equal to the mol-ecularities. For some special reactions (such as cocking) first order or an arbitrary order is assumed. Pseudo-rate coefficients are written in Arrhenius form. A systematic use of equilibrium constants, calculated from thermochemical data, is made for relating the rate coefficients of direct and reverse reactions. Generally, the net rate of the reversible reaction... 

This equation permits the calculation of equilibrium constants for polymerization-depolymerization from copolymer composition data extrapolated to zero Mi feed. The agreement between equilibrium constants calculated in this manner from free radical copolymerizations and those obtained from anionic homopolymerizations is shown in Table II, and again emphasizes the thermodynamic character of this work. 

Hence, the two routes, with and without reformer, have the same overall equilihrium thermodynamics at standard conditions, the same electrical power, zero Carnot power, and the same net circulator power. However, both the equilibrium constant calculation routes are approximate. The concentrations are in error as a result. See Section A.3.9. 

The realistic figures are Jco = 0.97 and = 0.03, and the large difference between the two pairs of y values comes from non-differentiation by the equilibrium constant calculation between the actual two-phase HjO product and an ideal gas ... 

A solution of one mole of butane and one mole of propane is heated to 100° F and 103.4 psia. Usiog equilibrium constants calculate the composition of the vapor and the liquid. Answer ScjHs = 0.408 J/caHj = 0.675. 

A system contains 25 mole per cent propane, 30 mole per cent pentane and 45 mole per cent heptane at 150° F. Using equilibrium constants calculate the composition of the liquid and vapor at 20 psia. Hint Assume Wj = 0.46 per mole of starting material.) What is the weight of liquid obtained per mole of starting material ... 

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