Chemical reaction Gibbs-Helmholtz equation

Gibbs-Helmholtz equation This equation relates the heats and free energy changes which occur during a chemical reaction. For a reaction carried out at constant pressure... 

Strategy The first step is to write a balanced equation for the chemical reaction. Then calculate AH° using Table 8.3 (page 209) and AS° using Table 17.1 (page 456). Finally, use the Gibbs-Helmholtz equation to determine AG° at 230°C (3 sig. fig.)... 

Consider the Gibbs-Helmholtz equation for the general chemical reaction written as in Eq. 9.3. For each of the species involved in the reaction,... 

When the pH is specified, we enter into a whole new world of thermodynamics because there is a complete set of new thermodynamic properties, called transformed properties, new fundamental equations, new Maxwell equations, new Gibbs-Helmholtz equations, and a new Gibbs-Duhem equation. These new equations are similar to those in chemical thermodynamics, which were discussed in the preceding chapter, but they deal with properties of reactants (sums of species) rather than species. The fundamental equations for transformed thermodynamic potentials include additional terms for hydrogen ions, and perhaps metal ions. The transformed thermodynamic properties of reactants in biochemical reactions are connected with the thermodynamic properties of species in chemical reactions by equations given here. 

Considering a nonlinear chemical reaction, a practical solution may be obtained by the integration of the Gibbs-Helmholtz equation from equilibrium to optimal state... 

Nernsf s formulation of the third law of thermodynamics was originally an ingenious solution to a crucial practical problem in chemical thermodynamics, namely, the calculation of chemical eqtiilibria and the course of chemical reactions from thermal data alone, such as reaction heats and heat capacities. Based on the first two laws of thermodynamics and van t Hoffs equation, chemical equilibria depended on the free reaction enthalpy AG, which was a function of both the reaction enthalpy AH and the reaction entropy AS according to the Gibbs-Helmholtz equation ... 

The present author has the impression from the literature on the stability of diazomethane relative to diazirine that two different physico-chemical phenomena were called (thermal) stability in some of the publications, namely the thermodynamic stability, as defined by the free energy of formation AGf and the free enthalpy of formation A//f for the (hypothetical) formation of a compound from the elements in a gas phase reaction under standardized conditions (298 K, 1 mol). AGf and A//f are related to one another by the free entropy A5f in the Gibbs-Helmholtz equation AGf = A/ff-TASf. The absolute values of AGf, A/ff and ASf do not give definite information on the stability of a compound, as this word is used in the everyday language of a chemist, because it is related to an unrealistic chemical process, namely the formation from the elements. If A/ff is known, however, for a given compound and for a real product of one of its reactions, the difference in magnitude of the two free enthalpies tells us whether this reaction is likely to take place, but we cannot depict at all, at least in principle, the half-life of such a reaction. 

The Gibbs-Helmholtz equation dG = dH — T dS yields the thermodynamics of chemical reactions. In the case of a negative free enthalpy dG, a spontaneous reaction occurs. Water splitting means a positive dH and dS, respectively. So it is only for very large T that spontaneous water decomposition occurs. As mentioned above, this means temperatures of about 2000 °C. For electrolysis, an electric potential in line with the free enthalpy dG is applied so the reaction can take place. The equation demonstrates that the required voltage sinks with higher temperatures. 

This is the Gibbs-Helmholtz equation. Since Equation 5.76 is linear in G and H, we may replace them by AG and AH, respectively, for a process, for example, a chemical reaction. If AH for the reaction may be determined with the help of a calorimeter, AG may also be determined. 

A special problem in applying thermodynamic calculations to such systems as irradiated fuel shall be discussed very shortly here this involves the question of whether conventional thermodynamic laws can be applied to mixed-phases systems showing very different concentration ranges of the individual constituents. Usually, in such calculations it is assumed that both the initial and the final states of a chemical reaction are well-defined compounds about which the relevant data of the basic Gibbs-Helmholtz equation... 

Gibbs-Helmholtz equation (physchem) An expression for the influence of temperature upon the equilibrium constant of a chemical reaction, d In K /iJT)p = AfTVRT, where K is the equilibrium constant, AH the standard heat of the reaction at the absolute temperature T, and R the gas constant. gibz helm,holts i,kw5-zh3n )... 

The identification of the free energy change of a chemical reaction with the electrical work done when the reaction takes place in a reversible cell can be justified experimentally in the following manner. By the Gibbs-Helmholtz equation,... 

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