In science, surface is an approximately-shaped two-dimensional region upon which an interaction or process may take place. The majority of the most complex and important earth-bound chemical processes and reactions, such as ocean floor activity, the Haber process, drug-receptor interactions, human chemical reactions (human existence), etc., take place on or near a surface. Shown below are few common examples:


DTA molecule "walking" on a surface.	Cluster about twenty E. coli bacteria (a bacteria molecule) attached and growing on a surface.	People (human molecules) walking on the surface of a bridge in daylight hours.

Haber process (1905): production of small amounts of ammonia NH3 from N2 and H2 at a temperature of 1000° C with the help of iron as a surface catalyst	Vacant and occupied bonding sites on a reactant surface available to different chemical species (A, B, A-B).	Octopus moving on a surface of ocean floor.

An ordered array of homes attached to a surface section of a Las Vegas suburb.	Diagram of two human molecules, 26-element molecules, attached to each other Mx≡Fy, via a human chemical bond, also each shown, Mx=E and Fy=E, attached to the surface of the earth molecule, a 92-element molecule, via an undefined type of chemical gravitation (gravity)?	Diagram of the different attractive and repulsive forces, e.g. ******-Van der Waals, electrostatic repulsion, hydrophobic interactions, etc., involved as a bacterium moves towards and attaches to a vertical surface**.

Technically, a surface is often considered as a “substrate”, thus acting as a catalyst functioning to lower the activation energy barrier to successful reaction, process actualization, or completed movement. The mechanisms of surface activity are studied in the science of “surface chemistry” and the heat, energy and work aspects of surface activity are studied in the science of “surface thermodynamics”.

In chemistry, the ability of a substance to influence the surface tension of a liquid is called “surface activity”; an example being the reduction in surface tension in water by the addition of a detergent. [1] A significant area of surface chemistry is concerned with the chemical reactions that occur at the interface between two phases, such as the reaction of a gas at the surface of a liquid.

References
1. Clark, John O.E. (2004). The Essential Dictionary of Science. Barnes & Noble.