Standard Gibbs-energy change

The standard Gibbs energy change of reaction, is used ia the calculation of equilibrium compositions the standard heat of reaction, is used iu... 

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 standard Gibbs-energy change of reaction AG° is used in the calculation of equilibrium compositions. The standard heat of reaclion AH° is used in the calculation of the heat effects of chemical reaction, and the standard heat-capacity change of reaction is used for extrapolating AH° and AG° with T. Numerical values for AH° and AG° are computed from tabulated formation data, and AC° is determined from empirical expressions for the T dependence of the C° (see, e.g., Eq. [4-142]). 

If Gf is arbitrarily set equal to zero for all elements in their standard states, then for compounds Gf = AG°, the standard Gibbs-energy change of formation for species i. In addition, the fugacity is eliminated in favor of the fugacity coefficient by Eq. (4-79),/ = yi jP. With these substitutions, the equation for becomes... 

A catalyst is a substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction the process is called catalysis, and a reaction in which a catalyst is involved is known as a catalyzed reaction. ... 

Fig. 1.1 (a) The ionization enthalpies of dipositive lanthanide ions with configurations of the type [Xe]4f" (upper plot left-hand axis), (b) The standard Gibbs energy change of reaction 1 (lower plot right-hand axis estimated value ... 

The standard Gibbs energy changes for the reactions of the reference compound are then calculated. They are listed in column 2 of table 2. 

Non-standard Gibbs energy changes can be calculated from the following equation. 

The standard Gibbs energy change AG° for the process is given by Eq. 6-28 ... 

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 intrinsic basicity (i.e. the standard Gibbs energy change for reaction 158 in the gas phase) for a variety of compounds XC(=S)Y have been determined by means of Fourier Transform Ion Cyclotron Resonance Spectroscopy (FT ICR) by the groups of Abboud39 and of Gal520. 

Mavrovouniotis, M.L. 1991. Estimation of standard Gibbs energy changes of biotransformations. /. Biol. Chem. 266,14440-14445. 

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). 

The definition of a catalyst, as per the International Union of Pure and Applied Chemistry (IUPAC), is that a catalyst is a substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction [1], The chemical process of increase of the reaction rate is called catalysis and the catalyst is both a reactant and a product of the reaction. That is, the catalyst is restored after each catalytic act. Besides, the catalyst does not influence the final equilibrium composition after the cessation of the reaction. 

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 final term AG° is the conventional way of representing the quantity GJ It is called the standard Gibbs energy change of reaction. 

The overall change in the Gibbs energy for the entire process, i.e., the sum of the changes for the five steps, is also the standard Gibbs energy change of reaction, because the overall result of the process is the conversion of reactants to products, all in their standard states. Therefore... 

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