Components

in biology, the species of plants that constitute a phytocenosis and vegetate annually, regardless of climatic conditions (in particular, independent of soil moisture).

Components differ from ingredients, which, although predominantly annual, vegetate only in years of sufficient moisture. Examples of components are feather grass and fescue. Sometimes the term “component” is used to designate any organism (including animals) in a biocenosis, or any living or non-living element of the biogeosphere, biogeocenosis, or ecosystem.

(in thermodynamics and chemistry), independent components, chemically individual substances that make up a thermodynamic system.

The term “components” does not refer to the total number of constituents but rather to the number of constituents that is sufficient to obtain the composition of any phase of a system. Thus, in a system consisting of calcium oxide, CaO, and carbon dioxide, CO₂, calcium carbonate is formed according to the reaction CaO + CO₂ ⇄ CaCO₃. In this system, we may consider CaO and CO₂ as the independent components and CaCO₃ as the product of their reaction. With equal justification, CaO and CaCO₃ can be considered as the components and CO₂ as the product of the thermal dissociation of CaCO₃.

It is characteristic of components that the mass of each component in a system does not depend on the mass of the other components; components may be independently introduced into a system and removed from it. Thus, in chemical systems in which the constituents enter chemical reactions, the number of components is determined by the difference between the number of constituent substances and the number of independent chemical reactions that may proceed in the system.

A system in which the substances do not react with one another is termed a physical system (for example, the liquid benzene-glycerin mixture). For such systems the number of components is equal to the number of constituents. Depending on the number of components, systems are termed one-component, two-component (binary systems), three-component (ternary systems), and multicomponent systems. The concept of components was introduced in 1875–76 by the American physicist J. W. Gibbs.