Free energy change of a chemical reaction

In order to appreciate the relationship between the free energy change of a chemical reaction and the cell emf, a reaction such as that of zinc metal with dilute sulfuric acid is considered ... 

A fuel cell is a device that converts the free energy change of a chemical reaction directly into electrical energy. This conversion occurs by two electrochemical half cell reactions. 

Given a listing of free energies of formation, the free energy change of a chemical reaction may he calculated in the same manner as you evaluated enthalpies of reaction and entropies of reaction. For the reaction that was discussed earlier,... 

Equation 14-5 relates the free-energy change of a chemical reaction to the electrical potential difference (that is, the voltage) that can be generated by the reaction. 

Note that the equilibrium constant Kp is, directly related by Eq. (2.9.9) to the differential free energy change of a chemical reaction under standard conditions. Further, the AGd value for the reaction under arbitrary, reversible, isothermal, and isobaric conditions involves the sum of AG and of a correction term RTY. Vi nPi. 

The free energy change of a chemical reaction is dependent on the activities of the substances in the chemical equation (Section 12-1 and Chapter 9). The relationship is... 

Fuel cells are galvanic cells, in which the free energy of a chemical reaction is converted into electrical energy via an electrical current. The Gibbs free energy change of a chemical reaction is related to the cell voltage via Equation 9-28 ... 

According to thermodynamics, the decomposition of MgC03 that is defined by Eq. (3.1), is a strongly endothermic reaction, since AH is positive, which is similar to most decomposition reactions [43-45]. Therefore, the decomposition is only sustained when the reactant is constantly heated. In thermodynamics, the Gibbs free energy change of a chemical reaction is given by ... 

The application of equation (2 33) for the purpose of measuring the free-energy change of a chemiced reaction will be referred to in detail at a later stage. 

Figure 11.22 A simple unified model for free energy change of a chemical reaction in solution. Each parabola is a function of the solvent displacement coordinate rand the solute reaction coordinate q. The minimal energy path followed by the system, as shown, involves both coordinates, just as in the toy model of Section 11.2.2.1. Here we do not couple the two motions, although we could. To apply transition state theory we need to know where is the lowest energy barrier and what is its height.

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,... 

The free energy change in a chemical reaction is expressed in the same way as the enthalpy of the reaction is expressed. For example, the free energy change in the reaction... 

Driving force is a term that is used to describe what provides most of the favorable free-energy change for a chemical reaction, that is, what makes it happen. We know that the AG for a chemical reaction that happens in the direchon written must be less than zero. If, for example, there is a chemical reaction in which the net enthalpy change (AH) is zero or... 

For the reaction aA + bB cC + t/D, the equilibrium constant is K = [C]l[D], /[A]"(B), Solute concentrations should be expressed in moles per liter gas concentrations should be in bars and the concentrations of pure solids, liquids, and solvents are omitted. If the direction of a reaction is changed. K = UK. If two reactions are added. A", = K, K-,. The equilibrium constant can be calculated from the free-energy change for a chemical reaction K = e AcrlRT. The equation AG = AH — TAS summarizes the observations that a reaction is favored if it liberates heat (exothermic, negative AH) or increases disorder (positive AS). Le Chatelier s principle predicts the effect on a chemical reaction when reactants or products are added or temperature is changed. The reaction quotient, Q, tells how a system must change to reach equilibrium. 

The value of the Gibbs free energy change for a chemical reaction at the temperature specified is given by the difference in Gibbs free energy between the products and the reactants. 

Fuel cell electrochemical reactions convert free energy change associated with the chemical reaction into electrical energy directly. The Gibbs free energy change in a chemical reaction is a measure of the maximmn net work obtainable from a chemical reaction [24]. 

What use can be made of this standard free-energy change for a chemical reaction The quantity AG° tells us whether a mixture of reactants and products, each present under standard conditions, would spontaneously react in the forward direction to produce more products (AG° < 0) or in the reverse direction to form more reactants (AG° > 0). Because A Gy values are readily available for a large number of substances, the standard free-energy change is easy to calculate for many reactions of interest. 

Assume that there is a chemical reaction taking place in the system. We can define the free energy change of this chemical reaction as usual (de Groot and Mazur 2013) ... 

An e.m.f. measurement is only useful for a thermodynamically reversible cell, when E is related to the free energy change of the chemical reaction by... 

The free energy of chemical reactions may be estimated both under the standard conditions and under real, or physiological, conditions. The standard free energy, AG°, of a biochemical reaction is defined as a free energy change under the standard conditions, i.e. at the concentration of reactants 1 mol/litre, temperature 25 °C <298 X), and pH 7. 

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