Gibb’s free energy of reaction

This analysis was performed by finding the Gibb s free energy of reaction (20) at the process temperature and relating this to the equilibrium constant, K, by the relation ... 

Calculations. The Gibb s free energy of the supersaturated solutions is given by AG = RTln(Q/K) = RTlnfKjp/Qjp) = -RTlnS, where K is the equilibrium constant and Q the activity ratio according to reaction (1). K,p is the solubility product for CaCO,(s). CaCO,(s) can exist in at least three crystal stmctures. It has been assumed that it is the most soluble form, known as vaterite, which is formed initially. Q,p is the corresponding product in the... 

The behaviour of the electrolyte can be imderstood in terms of the description of redox processes, which are processes by which the oxidation level of a substance can increase and decrease (reduction, hence "red-ox"), whereby ionic charges can be transported through the electrolyte. The relation between the potential difference across the electrolyte and the Gibb s free energy of the redox reactions... 

The physical properties normally needed in design and production are vapor pressure, heat of vaporization, density, surface tension, heat capacity and thermal conductivity. For chemical reactions, enthalpy of formation and Gibb s free energy of formation are helpful. Also, the boiling point, freezing point, molecular weight, critical properties, lower explosion limit in air and solubility in water are tabulated for each compound. This latter property data are helpful in safety and environmental engineering. 

The gas-phase acidity of a compound AH was defined as the variation in the Gibbs standard free energy of reaction (7.3). The equivalent process in a solvent S may be written as... 

Chemical systems spontaneously react in a fashion that lowers their overall free energy. At a constant temperature and pressure, typical of many bench-top chemical reactions, the free energy of a chemical reaction is given by the Gibb s free energy function... 

As a system moves from a nonequilibrium to an equilibrium position, AG must change from its initial value to zero. At the same time, the species involved in the reaction undergo a change in their concentrations. The Gibb s free energy, therefore, must be a function of the concentrations of reactants and products. 

The first term, AG°, is the change in Gibb s free energy under standard-state conditions defined as a temperature of 298 K, all gases with partial pressures of 1 atm, all solids and liquids pure, and all solutes present with 1 M concentrations. The second term, which includes the reaction quotient, Q, accounts for nonstandard-state pressures or concentrations. Eor reaction 6.1 the reaction quotient is... 

Alberty, R. A., 1969. Standard Gibb.s free energy, enthalpy, and entropy change.s a.s a function of pH and pMg for reaction.s involving adeno.sine pho.sphate.s. of Biological Chemistry 244 3290-3302. 

Under standard conditions, we can relate the change in Gibb s free energy for the preceding reaction to the standard emf of the cell ... 

It should be emphasized that an equilibrium can be established between a metastable phase(s) and its environment. Aragonite, for example, can be precipitated from seawater at 25°C, but it is unstable at Earth-surface T and P, and can persist metastably because of kinetic reasons. This statement is illustrated by the following calculation. We can use the free energies of formation of Table 6.1, and calculate the Gibbs free energy of reaction for the mass action equation representing aragonite-calcite equilibrium ... 

Measurements of the potentials of galvanic cells at open circuit give information about the thermodynamics of cells and cell reactions. For example, the potential of the cell in Figure 1, when the solution concentrations are 1 molar (1 M) at 25°C, is 1.10 V. This is called the standard potential of the cell and is represented by E°. The available energy (the Gibb s free energy AG°) of the cell reaction given in equation (3) is related to E° by... 

Linear free energy relationship (LFER) — For various series of similar chemical reactions it has been empirically found that linear relationships hold between the series of free energies (-> Gibbs energy) of activation AG and the series of the standard free energies of reactions AGf, i.e., between the series of log fc (k -rate constants) and log K (Kt - equilibrium constants) (z labels the compounds of a series). Such relations correlate the - kinetics and -> thermodynamics of these reactions, and thus they are of fundamental importance. The LFER s can be formulated with the so-called Leffler-Grunwald operator dR ... 

For each of the redox couples, the potential can be calculated using the Nernst equation. This equation correlates Gibb s free energy, known as AG, and the electromotive force provided by an oxido-reduction reaction (such a reaction acts as a galvanic cell). Given the following equation due to a chemical reaction ... 

Just like any other chemical reactions, synthetic reactions adhere to the principles of thermodynamics the study of energy and its interconversions. Is your desired product thermodynamically stable (can it be made and will it exist at room temperature and atmosphere) Will it be stable under your given synthetic conditions, including during and after isolation Gibb s free energy, AG, is our measure of the driving force for reactions, equation (1.10). 

Fig. 5 Gibb s free energy ehange for reactions of ZrBz and SiC with Ti and Ni calculated using the software HSC Chemistry version 4.1 (Outokumpu Ra, Oy, Finland).

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