Misapplication of the Clausius–Clapeyron equation for estimating heats of adsorption in foods


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It has been pointed out that the Clausius–Clapeyron equation which is currently used to measure isosteric heat of adsorption in reality measures the latent heat of evaporation. The usual Clausius–Clapeyron plot that decays rapidly to low values at low Aws has been compared with a suggested alternative equation derived directly from an expanded form of Caurie's unimolecular adsorption equation. The plot of the proposed equation is higher than that of the Clausius–Clapeyron equation, and it has the shape of an inverse sigmoid isotherm. Two discontinuities in the proposed plots are stated to demarcate three energy levels corresponding to three states of bound water recognised to exist along sigmoid food isotherm plots.