Moisture sorption free energy’ changes

Free Energy and Entropy Changes. The heat of sorption Qi consists of two parts, the free energy change AG and the entropy change AS. The loss in free energy AG (cal/g of water) can be calculated at any moisture content by... 

As implied by the proposal of Schuchmann et al. [7], many adsorption isotherms may be normalized by plotting the equilibrium moisture content against the free energy change of sorption (-i rin [10,11]. It is believed that desorption isotherms can be similarly correlated, particularly at moderate relative humidities when multimolecular adsorption is the dominant mechanism of attachment as the moisture content is directly related to the thickness of the adsorbate layer. Tests with particulate materials have shown that there is a linear relationship between the free energy change and In over a sixfold range in the latter [12]. This correlation implies an explicit relationship for the equilibrium moisture content of the kind... 

When wood below the fiber-saturation point interacts with water, heat is evolved, and there are changes in the free energy and entropy of the sorbed water. Furthermore, the wood exerts swelling forces that can be measured. These effects can be treated by classical thermodynamic methods although moisture sorption by wood is not a perfectly reversible process because sorption hysteresis is involved, as was pointed out in the section on Moisture Sorption Isotherms (p. 136). 

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