Gibbs free energy chemical reaction with

STRATEGY We write the chemical equation for the formation of HI(g) and calculate the standard Gibbs free energy of reaction from AG° = AH° — TAS°. It is best to write the equation with a stoichiometric coefficient of 1 for the compound of interest, because then AG° = AGf°. The standard enthalpy of formation is found in Appendix 2A. The standard reaction entropy is found as shown in Example 7.9, by using the data from Table 7.3 or Appendix 2A. 

The basic criterion for equilibrium with respect to a given chemical reaction is that the Gibbs free energy change associated with the progress of the reaction be zero. 

Entropy may also influence the spontaneity of chemical reactions. In general terms the entropy represents the disorder or randomness associated with a particular process. The Gibbs free energy of reaction includes both the enthalpy and entropy associated with chemical processes, and is defined as... 

We note that since we are considering the Gibbs free energy per atom, per molecule, or per reaction stoichiometry, this is by definition the chemical potential. We shall, however, genaally refer to this quantity as the Gibbs free energy, in line with keeping the nomenclature for all other concepts, which we express in per atomic-scale entities. 

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

The ends of a correctly constructed electrochemical circuit measuring electrical potential difference must always have metals or conductors with identical chemical composition. It is usually reached by simple connection of two metals by copper wires. The inclusion between two metal conductors of a third metal conductor according to Volta s law does not change the difference of potentials at the output of a circuit. The difference of potentials in an electrochemical circuit at equilibrium is caused by the change of Gibbs free energy during the appropriate electrochemical reaction ... 

Whether a reaction is spontaneous or not depends on thermodynamics. The cocktail of chemicals and the variety of chemical reactions possible depend on the local environmental conditions temperature, pressure, phase, composition and electrochemical potential. A unified description of all of these conditions of state is provided by thermodynamics and a property called the Gibbs free energy, G. Allowing for the influx of chemicals into the reaction system defines an open system with a change in the internal energy dt/ given by ... 

The tools for calculating the equilibrium point of a chemical reaction arise from the definition of the chemical potential. If temperature and pressure are fixed, the equilibrium point of a reaction is the point at which the Gibbs free energy function G is at its minimum (Fig. 3.1). As with any convex-upward function, finding the minimum G is a matter of determining the point at which its derivative vanishes. 

The computation of chemical equilibria can be posed as an optimization problem with linear side conditions. For any infinitesimal process in which the amounts of species present may be changed by either the transfer of species to or from a phase or by chemical reaction, the change in the Gibbs free energy is... 

Chemical work and chemical energy are defined in an analogous way. The intensity factor here is the chemical potential of a molecule or combination of molecules. This is stated as free enthalpy G (also known as Gibbs free energy ). When molecules spontaneously react with one another, the result is products at lower potential. The difference in the chemical potentials of the educts and products (the change in free enthalpy, AC) is a measure of the driving force of the reaction. The capacity factor in chemical work is... 

Though combushon is a very fast exothermic chemical reaction compared with other chemical reactions, the reaction time is finite and the combustion products are formed after a large number of molecular collisions, which also produce a large number of intermediate molecules. When the time-averaged numbers of molecules reach a constant level and the temperature becomes constant, the reachon system is said to be in a state of thermal equilibrium.Ii- - l The Gibbs free energy F for one mole of an ideal gas is defined according to... 

Figure 2.3 Comparison of the Michaelis-Menten model for a minimal kinetic scheme (bottom equation) with the pseudo second-order format (top equation). Relationship between the kinetic barriers for the formation of the Michaelis complex and the chemical transformation S -> P, and the Gibbs free energy of the (virtual) barrier for the pseudo second-order reaction S + —> P + E.

Chemical Equilibrium The chemical equilibrium approach is more complex computationally than applying the assumption of an infinitely fast reaction. The equilibrium composition of a multicomponent system is estimated by minimizing the Gibbs free energy of the system. For a gas-phase system with K chemical species, the total Gibbs free energy may be written as... 

An important motivation for studying entropy changes at low temperature is to obtain reaction entropies AS (5.76) that could be combined with thermochemically measured reaction enthalpies A7/rxn to give the Gibbs free energy changes for chemical reactions. Starting from the observation that... 

Early chemists thought that the beat of reaction, —AH. should be a measure of the "chemical affinity" of a reaction. With the introduction of the concepl of netropy (q.v.) and ihe application of the second law of thermodynamics lo chemical equilibria, it is easily shown that the true measure of chemical affinity and Ihe driving force for a reaction occurring at constant temperature and pressure is -AG. where AG represents the change in thermodynamic slate function, G. called Gibbs free energy or free enthalpy, and defined as the enthalpy, H, minus the entropy. S. times the temperature, T (G = H — TS). For a chemical reaction at constant pressure and temperature ... 

Helmholtz free energy (or Helmholtz energy) is the work obtainable from a system at a constant temperature and volume. It is much less used in chemistry than Gibbs free energy, because most chemical reactions occur at constant pressure, not constant volume. However, Helmholtz free energy is relevant to reactions with rapid pressure changes (explosions). 

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