Gibbs free energy, calculating changes

Gibbs free energy The change in the total energy of the system as calculated from the equation AG=AH TAS, where H is the change in the enthalpy, and AS is the change in the entropy of the system. 

FIGURE 8.12 Relationships between the amounts of unfrozen water and changes in the Gibbs free energy calculated from the NMR spectra recorded in (a) air or (b) CDCI3 for wheat seed roots after germinating for 3 or 7 days in different media. 

Appendix 1. Change in Molar Gibbs Free Energy Calculations. .. 391... 

Change in Molar Gibbs Free Energy Calculations... 

Having calculated the standai d values AyW and S" foi the participants in a chemical reaction, the obvious next step is to calculate the standard Gibbs free energy change of reaction A G and the equilibrium constant from... 

Example. Calculate the change in Gibbs free energy for the reaction of methanol and oxygen to produce formaldehyde and water at reaction temperatures of 600, 700, 800, 900, and 1,000°K ... 

A copy (5V4 inch floppy disk) of a menu-driven computer program to calculate Gibbs free energy of formation and change in Gibbs free energy for reactions (including random access data file of compound coefficients) is available for a nominal fee. For details, contact C. L. Yaws, Dept, of Chem. Eng. Lamar University, P.O. Box 10053, Beaumont, Texas 77710, USA. 

The enthalpy and Gibbs free energy change can be calculated from the functions involving H°m m by ... 

The decrease in Gibbs free energy as a signpost of spontaneous change and AG = 0 as a criterion of equilibrium are applicable to any kind of process, provided that it is occurring at constant temperature and pressure. Because chemical reactions are our principal interest in chemistry, we now concentrate on them and look for a way to calculate AG for a reaction. 

The changes in free energy of formation of Reaction (1) are shown in Fig. 2.1 as a function of temperature. " The values of AG were calculated using Eq. (1) above for each temperature. The Gibbs free-energy values of the reactants and products were obtained from the JANAF Tables.1 Other sources of thermodynamic data are listed inRef 6. These sources are generally accurate and satisfactory forthe thermodynamic calculations of most CVD reactions they are often revised and expanded. 

Once the standard states for the various species have been established, one can proceed to calculate a number of standard energy changes for processes involving a change from reactants, all in their respective standard states, to products, all in their respective standard states. For example, the Gibbs free energy change for this process is... 

As equation 2.4.8 indicates, the equilibrium constant for a reaction is determined by the temperature and the standard Gibbs free energy change (AG°) for the process. The latter quantity in turn depends on temperature, the definitions of the standard states of the various components, and the stoichiometric coefficients of these species. Consequently, in assigning a numerical value to an equilibrium constant, one must be careful to specify the three parameters mentioned above in order to give meaning to this value. Once one has thus specified the point of reference, this value may be used to calculate the equilibrium composition of the mixture in the manner described in Sections 2.6 to 2.9. 

Plan Calculate A7/fxn and ASfxn, then use the Gibbs free energy change equation, AG = AH - TAS, to... 

In a similar manner we calculate the Gibbs free energy change for the conversion of ADP to ATP ... 

Just like with the enthalpy and entropy, the standard Gibbs free energy change, (AG°), is calculated ... 

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