『Abstract
By studying the Free Energy of Activation, ΔG（＝に／を重ねる）,
of various geochemical transformations we have revealed the importance
of the contribution of the entropy of activation, ΔS（＝に／を重ねる）, in the energetics of the processes.
In studies performed so far including changes of phases, adsorption,
desorption, formation or breaking of bonds, ordering of ions,
etc. only the activation energy was considered as the main factor
determining the rate of the transformation process through the
Arrhenius equation. The above changes result in change of degrees
of freedom of the systems. If the above changes happen during
the “reactants to transition state or activated complex” step,
they result in changes of the entropy of activation. Through the
use of the Eyring-Polanyi equation and literature data we were
able to determine ΔG（＝に／を重ねる）
= ΔH（＝に／を重ねる） - TΔS（＝に／を重ねる） where ΔH（＝に／を重ねる）
is related to Eact = RT + ΔH（＝に／を重ねる）
and ΔS（＝に／を重ねる） is related to
A of the Arrhenius equation. It was found that the combination
of enthalpy and entropy of activation in ΔG（＝に／を重ねる）
gives a more realistic/true value of the energy requirements of
the activation step that the processes need in order to take place.
Also, an explanation is given of why calculated activation energy
values (that are related only to enthalpy of activation values)
for certain transformations deviate from the expected and observed
energy requirements that characterize the processes when the entropic
component is substantial. This analysis shows that similar processes
have similar ΔG（＝に／を重ねる） values
and therefore there is a way of foreseeing the ΔG（＝に／を重ねる）
of a process, if a number of similar processes have been studied
and their ΔG（＝に／を重ねる） values have
been calculated.
Keywords: Free Energy of Activation; Enthalpy of activation; Enthalpy
of Activation; Entropy of activation; Activation energy; Arrhenius
equation; Eyring-Polanyi equation』
1. Introduction
2. Effect of temperature on reaction rates
2.1. Theories of reaction rates
2.1.1. Collision theory
2.1.1.1. The Arrhenius activation energy
2.1.2. Absolute rate theory
2.1.2.1. The Eyring or activated complex theory relation -
Free Energy of Activation
3. The Arrhenius vs. the Eyring equation
3.1. Relation between Eact and ΔH（＝に／を重ねる）
4. Estimation of the errors
5. Application of the Eyring-Polanyi equation to important geochemical
processes
5.1. The role of ΔH（＝に／を重ねる）,
ΔS（＝に／を重ねる） and ΔG（＝に／を重ねる）
in certain geochemical processes and comparison with Eact
5.1.1. Crystallization and transformation of Fe-oxides and oxyhydroxides
5.1.1.1. Goethite and hematite crystallization under alkaline
conditions and in the presence of phosphate
5.1.1.2. Schwertmannite transformation to goethite and hematite
under alkaline conditions
5.1.1.3. Ferrihydrite transformation to goethite via the Fe(II)
pathway
5.1.2. cation ordering in natural and synthetic Mg(Al,Cr)2O4 spinels
5.1.2.1. Cation ordering in synthetic MgAl2O4 spinel
5.1.2.2. Cation ordering in natural Mg(Al,Cr3+)2O4 spinels
5.1.2.2.1. Low-Cr samples
5.1.2.2.2. High-Cr samples
5.1.2.2.3. Synthetic sample (Syn) MgAl2O4
5.1.3. Kinetics in base metal sulfides
5.1.3.1. Exsolution kinetics in base metal sulfides
5.1.3.1.1. Exsolution of pentlandite (Ni,Fe)9S8 from the monosulfide solid solution (Fe,Ni)S
5.1.3.1.1.1. Mss (monosulfide solid solution) composition
Fe0.9Ni0.1S
5.1.3.1.1.2. Mss (monosulfide solid solution) composition
Fe0.8Ni0.2S
5.1.3.1.1.3. Exsolution of pyrite from pyrrhotite of bulk
composition Fe0.862S
5.1.3.2. Transformation kinetics in base metal sulfides
5.1.3.2.1. Transformation of synthetic mackinawite to hexagonal
pyrrhotite
5.1.3.2.2. The marcasite-pyrite transformation
5.1.4. The α-NiS oxidation in the temperature range 670-700℃
5.1.5. Barite dissolution and precipitation in water and sodium
chloride brines (at 44-85℃)
5.1.5.1. Dissolution experiments
5.1.5.2. Precipitation experiments
6. significance and usefulness of the thermodynamic parameters
7. Conclusions
Acknowledgements
References