In thermodynamics, a component is one of a collection of chemically-independent constituents ofa system. The number of components represents the minimum number of independent species necessary to define the composition of all phases of the system. In thermodynamics, a component is one of a collection of chemically-independent constituents ofa system. The number of components represents the minimum number of independent species necessary to define the composition of all phases of the system. Calculating the number of components in a system is necessary when applying Gibbs' phase rule in determination of the number of degrees of freedom of a system.