What does chemisorption mean?
Chemisorption is the process by which atoms or molecules attach to the surface of a solid through the formation of true chemical bonds, rather than the weak intermolecular attractions responsible for ordinary adsorption. Because covalent or coordinate bonds are involved, chemisorption releases far more heat and is generally irreversible under ordinary conditions; a molecule bound this way may even break apart or transform upon attachment. The phenomenon is central to heterogeneous catalysis — reactions such as ammonia synthesis and catalytic hydrogenation depend on reactants chemisorbing onto a metal surface before reacting. Chemists characterize it using quantities like the heat of chemisorption and chemisorption isotherms. Although strictly a technical term confined to chemistry, surface science, and materials engineering, it captures a concept of great practical importance, describing the very first step by which many industrial processes convert raw materials into useful products.
nounAdsorption in which the adsorbed molecules form strong chemical bonds with the surface of the adsorbent, typically involving energies far greater than those of physical adsorption.
- The process in which atoms or molecules adhere to a solid surface by forming chemical (covalent or coordination) bonds, as distinct from weak physical adsorption.
"The catalyst's activity depends on the chemisorption of reactant molecules onto its metallic surface."
"Nitrogen undergoes chemisorption on the iron catalyst during ammonia synthesis."
"The researchers measured the heat of chemisorption to determine how tightly oxygen bound to the metal surface."
Rarely pluralized; chemisorption is normally treated as an uncountable process noun in scientific writing.
"Different chemisorptions were observed across the various metal surfaces."
Unlike ordinary surface sticking, chemisorption creates genuine chemical bonds — so strongly that the molecule can be permanently altered, which is exactly how many industrial catalysts do their work.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of chemisorption
The word combines 'chemi-', from 'chemistry', with '-sorption', the shared ending of absorption and desorption, reflecting its status as the chemical-bonding counterpart of physical adsorption. It was coined in the early twentieth century as surface chemistry matured into a distinct discipline, particularly through work on catalysis. Its sibling terms 'adsorption' and 'absorption' derive from Latin roots (ad-/ab- plus sorbere, 'to suck in'), while the chemical element traces to 'alchemy' via Arabic 'al-kīmiyā'.
Related word forms
How chemisorption is actually used
A technical term used almost exclusively in chemistry, surface science, catalysis, and materials engineering; rarely encountered outside scientific literature. Typically treated as uncountable or mass noun in technical writing, though it can bear a plural in some contexts.
Easily confused with chemisorption
Physisorption involves weak van der Waals forces holding molecules to a surface, whereas chemisorption involves actual chemical bond formation and much higher adsorption energies.
Adsorption is the general term for molecules accumulating on a surface, of which chemisorption is the specific subtype involving chemical bonding.