Entropy change of reaction

In accord with this, AH° is defined by Eq. (4.14) and ACp by Eq. (4.16). For the standard entropy change of reaction AM0 becomes AS°. These quantities are all functions of temperature only for a given reaction, and are related to one another by equations analogous to property relations for pure species. 

AG = Gibbs energy change of reaction (1), J/mole A AH° = Standard Enthalpy change of reaction (1), J/mole A AS° = Standard Entropy change of reaction (1), J/mole A K r = Cell efficiency, E/E... 

Forster cycle Indirect method of determination of excited state equilibria, such as pK values, based on ground state thermodynamics and electronic transition energies. This cycle considers only the difference in molar enthalpy change (AAH) of reaction of ground and excited states, neglecting the difference in molar entropy change of reaction of those states (AAS). 

The entropy changes of reactions between ions deserve special mention. For reactions between ions of unlike sign there is an entropy increase in going from reactants to activated complex. This is because the activated complex will have less charge than the reactants and will become partially desolvated. For ions of the same sign, however, the activated complex will be more charged than the reactants. This one would expect to be strongly solvated. There is a loss of entropy, therefore, when the activated complex is formed. For examples which confirm these relationships, see references [5, 11, 20]. 

Required energies and entropy changes of reaction for HHLT are shown in Table 1. In HHLT, total required electrical energy is 113.4 kJ/mol for 1 mol H2 production and it is about half of direct water splitting (204.9 kJ/mol at 500°C, [5]). 

The entropy change of reaction provides a measure of the change in molecular disorder or randomness caused by a reaction. 

Note that these entropies are with respect to the entropy equal to zero for the pure component and 0 K. Also, the entropy change of reaction at 0 K is zero for all reactions. Therefore... 

Defining the term on the right-hand side to be the standard entropy change of reaction, A5" gives... 

If the cell does not contain a gas electrode, then since the entropy changes of reactions in solution are frequently rather small, less than 50 J/K, the temperature coefficient of the cell potential is usually of the order of 10 " or 10 V/K. As a consequence, if only routine equipment is being used to measure the cell potential and the temperature coefficient is sought, the measurements should cover as wide a range of temperature as is feasible. 

Analogous to the standard enthalpy change of a reaction (see Equation 7.41), the standard entropy change of reaction is given by the difference in standard entropies between the products and reactants ... 

Gibbs free energy change of reaction [J/mol] Entropy change of reaction [J/mol K] Faraday constant [96,485 C/mol] oxygen flux density [mol/cm s] surface exchange coefficient [cm/s] partial oxygen pressure [bar] gas constant [8.314 J/mol K] ionic conductivity [S/cm] electronic conductivity [S/cm] temperature [K]... 

The standard Gibbs free-energy change of reaction, A G , is related to the enthalpy change of reaction and the entropy change of reaction (A S ). 

AS = entropy change of reaction T = absolute temperature K = equilibrium constant (mass law)... 

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