Chemical reaction standard state Gibbs energy change

One identifies the stoichiometric-coefficient-weighted sum of pure-component chemical potentials in the reference states, at unit fugacity, with the standard-state free-energy change for chemical reaction, since [pi, pure(/ )l° is equivalent to the molar Gibbs free energy of pure component i in this reference state. Hence,... 

STANDARD-STATE FREE ENERGIES The change in the Gibbs free energy for a chemical reaction performed at constant temperature is... 

As with all chemical reactions, the standard state Gibbs free energy change for an isotope exchange reaction at a given pressure and temperature is related to the equilibrium constant by ... 

Often there is confusion as to the definition of the term catalysis. A reaction is catalyzed if its rate is accelerated relative to the noncatalyzed pathway. A catalyst serves to alter the reaction mechanism of a chemical process by providing a new pathway with a lower potential-energy barrier. The Union of Pure and Applied Chemistry (lUPAC, 1981) definition of the term catalyst states that a catalyst is a substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction the process is called catalysis, and a reaction in which a catalyst is involved is known as a catalyzed reaction. ... 

Use has here been made in steps 2 through 4 of the fact that there is no change in the Gibbs energy for processes carried out under conditions of membrane and chemical-reaction equilibrium. This explains why the value of AG° is related directly to the ratios of the equilibrium-state and standard-state fugacities (ft = 1). 

Because G is a state function, chemical equations can be added together—with their AG° values combined as in Hess s law for changes in enthalpy—to calculate Gibbs free energy changes for chemical reactions under standard-state conditions. 

If a chemical reaction takes place at constant temperature and pressure under conditions such that all the components are in their standard state, then the value of the change of the Gibbs free energy, AZ0f will be... 

In both the stoichiometric and nonstoichiometric approaches to reaction-equilibrium calculations, we need values for the standard change in the Gibbs energy Ag. In the stoichiometric development, is used in (10.3.14) to obtain values for the equilibrium constant K in the nonstoichiometric development, is used to obtain values for the standard-state chemical potentials that appear in (10.3.38). Since is a state function, values for can be measured or computed along any convenient process path that starts with the desired reactants in their standard states and ends with products in their standard states. Of those many possibilities, the most convenient is to determine Ag° by combining the Gibbs energies of formation for each species. That procedure is developed here. However, values for molecular properties of formation are often available only at a particular temperature T°, so we must be able to correct those values to the reaction temperature T. Such corrections for A require values for the standard heat of reaction Aft and, perhaps, values for the standard isobaric heat capacities Ac. ... 

The change in Gibbs free energy of a system, when reactants in their standard states are converted to products in their standard states, is called the molar standard free energy change (AG ) for the reaction. The superscript zero to the G indicates the standard state and the overbar indicates that the molar amounts of the reactants and products given by the numerical coefficients in the balanced chemical equation for the reaction are involved. For the forward reaction of the general chemical reaction (1.5)... 

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