Question

What is the effect of temperature on chemisorption?

Answer 1

Chemisorption is the process of adsorption which involves a chemical reaction between the surface and adsorbate. In chemisorption breaking of bonds takes place and new bonds are formed.

Complete answer:
Effect of temperature:
Chemisorption involves the formation of new bonds and breaking of old bonds. It is an exothermic process and favours high temperature so that old bonds between surface and adsorbate get broken.
Due to specificity, the nature of chemisorption can greatly differ, depending on the chemical identity and the surface structural properties. The bond between the adsorbate and adsorbent in chemisorption is either ionic or covalent.
Uses:
In heterogeneous catalysis, reaction of molecules with each other takes place by the formation of chemisorbed intermediates. After the chemisorbed species that are adsorbate and adsorbent combine (by forming bonds with each other) the product gets desorbs from the surface.
Hence, chemisorption increases with an increase in temperature.

Additional Information:
Dissociation Chemisorption:
As in the gas-surface chemisorption, the dissociation of diatomic gas molecules takes place, such as hydrogen, oxygen, and nitrogen.
A model used to describe the process is named as precursor-mediation. The absorbed molecule gets adsorbed onto a surface into a precursor state. The molecule of gas then diffuses across the surface to the chemisorption sites. After that they break the molecular bond to form new bonds to the surface. The energy which is used to overcome the activation potential of dissociation comes from the translational energy and vibrational energy.

Note:
Chemisorption increases with an increase in temperature upto a certain limit and then after that, it starts decreasing as further high temperature helps in breaking the bonds between the absorbed molecules and the adsorbate.