Respected all Experts,
I have found different perception author to other author regarding enthalpy value for type of adsorption.
According khan et all (2010) (attached here) the change in adsorption enthalpy (H◦) for physisorption is in the range of −20 to 40 kJ/mol, but for chemisorption it is between −400 and −80 kJ/mol
so what about this between gap of -20 KJ/mol to -80 KJ/mol and above value of 80kj/mol ??
Is negative value of enthalpy represent chemisorption?
Others authors consider that a change of enthalpy
Generally other factors should be considered in deciding the type of sorption. Basically you need to have a perception of the interactions between sorbates and sorbent without which the enthalpy alone is not sufficient factor.
Hi,
The enthalpy is low for physical adsorption compared with chemical adsorption.
Thank you so much Abdollah Golchoobi
Agreed with you,that other factors should be considered while deciding the type of adsorption.But sir,when we look into delta H value,which value or range should be differentiate physical adsorption and chemical adsorption??
thanks
thank you Luma M. Ahmed
Low enthalpy means which range..i found different ranges author to author.which one is authentic?
In the ranges you indicated not having overlap it is clear. In the ranges there is overlap, the only option to decide the type of sorption would be to scrutinize the background interactions .
As for the adsorption mechanism, it is much better to rely on physicochemical studies on the adsorbent surface than on the value of adsorption enthalpy. It is also worth asking the authors whether the given enthalpy values were measured or determined from the van't Hoff equation. In the latter case, another problem arises with the reliability of the values of the equilibrium constants.