Changes in Gibbs Free Energy

Chemical equilibrium for a reaction is associated with the change in Gibbs free energy (AG ) ealculated as follows ... 

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 equilibrium constant of a reaction can be related to the changes in Gibbs Free Energy (AG), enthalpy (AH) and entropy (AS) which occur during the reaction by the mathematical expressions ... 

In some cases, an alternative explanation is possible. It may be assumed that any very complex organic counterion can also interact with the CP matrix with the formation of weak non-ionic bonds, e.g., dipole-dipole bonds or other types of weak interactions. If the energy of these weak additional interactions is on the level of the energy of the thermal motion, a set of microstates appears for counterions and the surrounding CP matrix, which leads to an increase in the entropy of the system. The changes in Gibbs free energy of this interaction may be evaluated in a semiquantitative way [15]. 

The change in Gibbs free energy for a process is a measure of the change in the total entropy of a system and its surroundings at constant temperature and pressure. Spontaneous processes at constant temperature and pressure are accompanied by a decrease in Gibbs free energy. 

This important relation tells us that, if we know the change in Gibbs free energy of a process taking place at constant temperature and pressure, then we immediately know how much nonexpansion work it can do. For instance, for the oxidation of glucose,... 

To find the connection between cell potential and Gibbs free energy, recall that ir Section 7.14 (Eq. 21) we saw that the change in Gibbs free energy is the maximum nonexpansion work that a reaction can do at constant pressure and temperature ... 

H=U + PV G = H-TS Change in Gibbs free energy at constant temperature ... 

To see how the catalyst accelerates the reaction, we need to look at the potential energy diagram in Fig. 1.2, which compares the non-catalytic and the catalytic reaction. For the non-catalytic reaction, the figure is simply the familiar way to visualize the Arrhenius equation the reaction proceeds when A and B collide with sufficient energy to overcome the activation barrier in Fig. 1.2. The change in Gibbs free energy between the reactants, A -r B, and the product P is AG. 

Ostwald ripening is driven by the positive surface energy, the specific, per gram amount of which can be lessened with particle growth. The change in Gibbs free energy when a particle forms is composed of two terms, a bulk term and a surface term as... 

Figure 3. Change in Gibbs free energy upon formation of a nanoparticle from solvated atoms.

The 1.8 kcal mol 1 less favorable change in Gibbs free energy for the addition of water to [18+] to give [18]-OH in 50/50 (v/v) trifluoroethanol/water (p/CR = -11.3)104 than for addition of water to Me-[6+] in the same solvent (pATR = -12.6)13 shows that the former carbocation is stabilized relative to the alcohol. This stabilization may be the result of the smaller entropic price paid to restrict the / —CH bonds in the five-membered ring at [18+] to conformations that are favorable for hyperconjugation with the cationic carbon. 

The presence of ionic moieties in hydrogels makes the theoretical treatment of swelling much more complex. In addition to the AGm xing and AGgiastic in Eq. (1), there is an additional contribution to the total change in Gibbs free energy due to the ionic nature of the polymer network, AG on c. 

The change in Gibbs free energy, AG, for this process is the difference between the solution and gas-phase chemical potentials. Using the chemical potential of each of the species in the gas phase and in solution and Equation 8.16 gives ... 

Chemical potential The change in Gibbs free energy associated with the compositional change of each species. 

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