Equilibrium constants relative reaction enthalpies from

It should be stressed that the condition ArX 0 is not required to derive a series of relative values of reaction enthalpies from single-temperature equilibrium constants. We only need to ensure that Arremains constant. Consider, for example, the case of reaction 14.33 (see figure 14.5) ... 

As to the computation of reaction enthalpies and entropies, AH and AS , the same arguments apply if they have been obtained from the temperature dependence of the equilibrium constant. A different situation arises vdien AH is determined directly from calorimetry, say with a constant relative error 6. The standard entropy AS then has the standard error... 

Solvent effects and adduct formation of [VO(acac)2l and other [VO(j8-diketonato)2] complexes have been studied by several methods361,366,52 -532 and in coordinating solvents [VO(acac)2] is known to add a sixth ligand according to equation (36). Older reports include a spectrophotometric and calorimetric study of [VO(acac)2] and [VO(tfacac)2] adducts.521 With [VO(acac)2] in nitrobenzene, the enthalpy change for reaction (36) ranges from 44.3 kJ mol-1 for n-decylamine to 24.3 kJ mol-1 for methanol. Equilibrium constants K were between 1000 and —0.6. [VO(acac)2] is not a sensitive indicator of relative base strength.521 For [VO(acac)2], A0 decreases by —3 G (and go increases by —0.0004) as amine adducts are formed.522... 

Often the enthalpy of reaction is obtained by measuring the equilibrium constant of an acid-base reaction over a range of temperatures. If In K is plotted versus l/T. the slope will be equal to -AH/R. Thus various experimental methods have been devised to measure the equilibrium constant by spectrophotometric methods. Any absorption which differs between one of the reactants (either acid or base) and the acid-base adduct is a potential source of information on the magnitude of the equilibrium constant since it gives the concentration of two of the three species involved in the equilibrium directly and the third indirectly from a knowledge of the stoichiometry of the reaction. For example, consider the extensively studied reaction between organic carbonyl compounds and iodine. The infrared carbonyl absorption is shifted in frequency in the adduct with respect to the free carbonyl compound. Thus the equilibrium mixture exhibits two absorption bands in the carbonyl region of the spectrum (Fig. 9.1) and the relative concentrations of the free carbonyl and the adduct can be obtained.3- Alternatively, one can observe the absorption of the iodine molecule, U, in... 

Most of the existing quantitative data on proton affinities and gas-phase basicities have been derived from determinations of equilibrium constants for proton transfer reactions (Eqn [8]) in the gas phase (Eqns [9] and [10]). Note that the measurement of a series of equilibrium constants at a single temperature will generate relative, rather than absolute, values for gas-phase basicities. In order to determine the enthalpy change of Equation [8] - that is, the relative... 

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