for adsorption value of change in enthalpy is
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Adsorption at the Liquid–Solid Interface: Thermodynamics and Methodology
Françoise Rouquerol, ... Kenneth Sing, in Adsorption by Powders and Porous Solids, 1999
Definition of displacement enthalpies (and energies)
The enthalpies of adsorption as already defined are adequate for an experiment when a clean adsorbent is immersed in the solution, but they are not suited for other experiments, which are usually more accurate where the adsorbent is initially immersed in the pure solvent. When the pure solvent is replaced by a solution of molality b2, adsorption of the solute can only take place by displacement of the solvent. The word ‘displacement’ is used here to indicate that the adsorption of the amount n2σ(n) of solute produces the desorption of a corresponding (but usually not equal) amount of solvent. Following Kiraly and Dekany (1989), let us call r the amount of solvent displaced (i.e. desorbed) by one mole of solute, therefore producing a change in composition of the solution and giving an enthalpy of mixing, ΔmixH, which is part of the overall heat effect, Qexp, measured during the experiment. It is preferable not to include ΔmixH (which is not a property of the interface) in the definition of the enthalpy of displacement, which is therefore:
(5.70)Δdp1H1.2=Qexp−ΔmixH
Françoise Rouquerol, ... Kenneth Sing, in Adsorption by Powders and Porous Solids, 1999
Definition of displacement enthalpies (and energies)
The enthalpies of adsorption as already defined are adequate for an experiment when a clean adsorbent is immersed in the solution, but they are not suited for other experiments, which are usually more accurate where the adsorbent is initially immersed in the pure solvent. When the pure solvent is replaced by a solution of molality b2, adsorption of the solute can only take place by displacement of the solvent. The word ‘displacement’ is used here to indicate that the adsorption of the amount n2σ(n) of solute produces the desorption of a corresponding (but usually not equal) amount of solvent. Following Kiraly and Dekany (1989), let us call r the amount of solvent displaced (i.e. desorbed) by one mole of solute, therefore producing a change in composition of the solution and giving an enthalpy of mixing, ΔmixH, which is part of the overall heat effect, Qexp, measured during the experiment. It is preferable not to include ΔmixH (which is not a property of the interface) in the definition of the enthalpy of displacement, which is therefore:
(5.70)Δdp1H1.2=Qexp−ΔmixH
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