Glossary
Absorption (spectroscopy): Absorption processes are processes in
which energy from a photon is transferred to a molecule or
material, promoting it to an excited state.
Activity (chemical): The availability of a species to participate in a
reaction. Activity is proportional to concentration.
Adiabatic process: A process in which there is no heat transfer between
the system and surroundings.
Adsorbate: A term used to describe an atom, ion, or molecule that is
either deposited onto a surface or is the species to be adsorbed.
Adsorbent: Surface upon which an adsorbate is deposited.
Adsorption isotherm: A plot of how the amount of adsorbate on a given
adsorbent changes with pressure (for gas-phase deposition) or
concentration (for liquid-phase deposition).
Aggregation: Buildup of material at an interface. The term also describes
the formation of clusters or an increased local concentration of
molecules (e.g., micelle) in bulk phases.
Aggregation number: Number of molecules that comprise a single
micelle.