According to Adsorption Thermodynamics ΔG can be calculated from two equations
ΔG = ΔH - TΔS --- (1)
ΔG = RTln Kc ---- (2)
The values of ΔH and ΔS are calculated from the slope and intercept of the linear regression of ln (Kc) versus 1/T
Where
Kc = CA/CS
CA (mg/L) is the amount of adsorbate adsorbed at equilibrium and CS (mg/L) is the amount of adsorbate that remained in the solution at equilibrium.
The real question is
Values of ΔG calculated from Eq (1) & (2) should have the same values but Why it does not?
How the value of ΔG is really calculated?
Why the interpretation of the ΔH & ΔS is different in different research articles?
What is the real interpretation of ΔH & ΔS results?
The calculation of delta G is done first followed by the calculation of delta H and delta S. The values of delta G calculated from both equation varies because when we calculate delta H and delta S we calculate them by doing linear regression and you may know that when regression is done, it takes into consideration approximation, not precise values of delta H and delta S corresponding to data input. Now, when the delta H and delta S are approximate values, it is certain that the delta G calculated using these values will be approximate only and hence the difference is seen in delta G values calculated from two equations.
Thank you Abhishek.
How are the values of ΔH & ΔS are interpreted?
This is a trivial question. delta H if positive means that the reaction is endothermic and if negative means that the reaction is exothermic. Further, if delta S is positive, then there is increase in randomness or entropy and if negative, there is decrease in randomness.
First of all, i think you are talking about DG°, DH° and DS°. Their values are related to the selected units of measure (standard state).
See Article Considerations about the correct evaluation of sorption ther...
Kc = cAe / cSe = const.? So your equilibrium data is described by the Henry adsorption isotherm. Is that in your case? Regards,
plz to calculate the Boltzmann equation K = e(- ΔG / KT) how can i calculate the ΔG via G theoretical ? (ΔG =G product -G reactant ) ? thank u for advance?
Please see my recent article:Article Opportunities and constraints of using the innovative adsorb...
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