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Frequently Asked Question
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Derive the formulas formulas for enthalpy of adsorption and entropy of adsorption
Accepted Answer
The enthalpy and entropy of adsorption can be derived using the following relationships:
Enthalpy of Adsorption (ΔHads)
The enthalpy of adsorption is the change in enthalpy when one mole of adsorbate is adsorbed onto a solid surface. It can be determined experimentally using calorimetry or by using the following relationship derived from the Clausius-Clapeyron equation:
ΔHads = -R
(d ln K / d(1/T))
where:
ΔHads is the enthalpy of adsorption
R is the ideal gas constant
K is the equilibrium constant for adsorption
T is the temperature
Entropy of Adsorption (ΔSads)
The entropy of adsorption is the change in entropy when one mole of adsorbate is adsorbed onto a solid surface. It can be determined using the following relationship derived from the Gibbs free energy equation:
ΔSads = (ΔHads - ΔGads) / T
where:
ΔSads is the entropy of adsorption
ΔHads is the enthalpy of adsorption
ΔGads is the Gibbs free energy of adsorption
T is the temperature
Note: The negative sign in the enthalpy equation indicates that adsorption is typically an exothermic process. The entropy of adsorption is usually negative, indicating a decrease in disorder upon adsorption. These relationships are based on the assumption that the adsorption process is reversible and follows the Langmuir isotherm model.
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