A Simple Way of Calculating the Change in the Gibbs' Free Energy of Ion Adsorption Reactions

Adsorption experiments of Zn 2+ and Cd 2+ ions from aqueous solutions onto vermiculite were conducted to test the applicability of two basic functions derived for calculating the change in the Gibbs' free energy (ΔG 0 ) and the chemical potential (Δμ) between the initial and equilibrium states in ion adsorption systems. The functions were deduced on the basis of the thermodynamic principle that the chemical potentials of the reactants and products of a physicochemical reaction should be equal in the equilibrium state and, consequently, the change in the Gibbs' free energy between the initial and equilibrium states of the reaction should be equal to the sum of the initial molar quantity of each reactant multiplied by its change in chemical potential. The results of the analysis conducted indicate that the two functions considered could well be used not only for calculating ΔG 0 and Δμ but also for determining the adsorption capacity of an adsorbent under the conditions considered.