Surface chemistry is the discipline of chemistry concerned with the processes that occur at the interfaces between phases, particularly between liquid and gas. Surfaces are important in catalysis, colloid formation, electrode reactions, chromatography, and other processes. Understanding how molecules and atoms interact with surfaces and with one other while on surfaces is critical to understanding both desirable and unfavorable chemical reactions, such as heterogeneous catalysis and corrosion chemistry. The study of chemical reactions at interfaces is roughly defined as surface chemistry. It is closely related to surface engineering, which tries to modify a surface's chemical composition by incorporating selected materials or functional groups that generate various desired effects or improvements in the surface or interface's qualities.