38
comparing this to the spectral shift accompanying aggrega
tion (504 nm to 464 nm) corresponding to 4.8 Kcal/mole dye
separation in energy between the ground and excited states,
he concluded that the spectral shift results from an
increase in energy of the excited state, rather than a
decrease in the ground state.
Enthalpy and entropy changes, AHand ASrespectively,
of reactions may be determined from the relationship be
tween the equilibrium association constants for the processes
at various temperatures and the temperature as set forth
by the van't Hoff relationship.
l0g K 2.303R T
(1-31)
+ Constant
This important equation will be derived below (73).
For ideal systems, any change in the total free
energy, G, can be said to be due to changes in either
temperature or pressure, since the state function, G,
can be defined in terms of pressure, volume, and temperature.
(1-32)
We define
G = H TS
(1-33)
and
H = E + PV
(1-34)
where H is the enthalpy, S is the entropy, and E is the