The activation energy value is given in following reference:

Atkins' "Physical chemistry" book.

Dear Dr. Farid Benyahia,

First, many thanks for your reply.

I agree with you that the physisorption needs less energy than chemisorption, since the chemisorption results in the formation of a chemical bond and is typified by a much stronger adsorption energy than physical adsorption. But the physisorption is affected by the activation energy, i.e. it needs also an activation energy to be done.

the value of the activation energy determines the type of sorption process; if it has a large value, it will be a chemisorption, while if it has a low value, it will be a physisorption. I need a reference shows that the value of the activation energy for chemisorption is greater than 20 KJ/mol not greater than 40 KJ/mol. Thank you and you are welcome.

Dear Dr. Amin Shavandi,

Thank you for your answer.

I agree with you that chemisorption is an exothermic process as it involves formation of chemical bonds. But the extent of chemisorption increases with increase in temperature up to certain limit and then after that it starts decreasing.

You said that the value of enthalpy 0-20 Kj/mol gives a physical and above 80 kj/mol gives chemical, what about the values from 20-80 KJ/mol?

I read in some published papers that if the value of activation energy greater than 20 KJ/mol, chemisorption will be obtained, and in other papers; if it is greater than 40 KJ/mol, it will be chemisorption. and I recommend the value > 20 KJ/mol, so, I need more references to confirm this statement.

Best regards.

Dear Ali Nematollahzadeh,

Thank you for your kind reply.

Best regards.

My dear Farid,

Thank you very much for your interest.

The reference that you mentioned contains the statement "if the value of activation energy, Ea, (calculated from Arrhenius equation) greater than 40 KJ/mol, the sorption will be a chemisorption". But I need a reference confirms that if the value of activation energy greater than 20 KJ/mol, a chemisorption will be obtained.

I am still searching for that reference.

Best regards.

Dear Zheng Feei Ma,

Many thanks for your efforts and reply.

The site that you sent includes valuable information about types of sorption, But I need a published paper to be mentioned as a reference.

Best regards.

Dear Farid Benyahia

The paper that you mentioned contains values for activation energy (Ea), but I tried to check the calculations of Ea, I found that there are errors in the calculation of Ea in Table 4 in the published paper, since DeltaH=Ea-RT, by using this equation to calculate the value of Ea, the results are different from the values of Ea in Table 4.

S.s. Metwally

Dear Metwally,

Can I kindly ask you if you find reference for what you ask in this question to share it with me?

Dear Noor Aljammal ,

Sure I will do.

I hope that you share also if you find it.

Best regards.

S.s. Metwally thank you so much..sure I will

Agreed with @ Farid Benyahia

I am also looking for a reference where I can find that value nearing -40kJ/mol can be termed as chemisorption

Dear Melwally, Can't we use the Arrhenius equation for calculation the activation energy?

If you have an estimation of delta(H) that might help you to identify the adsorption process as well. I think that is a better parameter to rely compared to activation energy to understand the type of adsorption. Alternatively you can calculate the DLVO interaction energy and compare it for the range of physisorption.

Activation energy only makes sense for elementary processes. Certainly equilibrium adsorption is not an elementary process. There are two opposite phenomena. So we can talk about the activation energy of these two phenomena - for each separately.

Thank you for your response

Mohamed I. Aly

Dubinin–Radushkevich isotherm does not state that the value of activation energy is greater than 20 KJ/mol.