Homogeneity and heterogeneity

For other meanings of heterogeneity, homogeneity, and related words, see Heterogeneity (disambiguation) and Homogeneity (disambiguation).

Homogeneity and heterogeneity are concepts relating to the uniformity or lack thereof in a substance. A material that is homogeneous is uniform in composition or character; one that is heterogeneous lacks uniformity in one of these qualities.

The concepts are applicable to combinations at every level of complexity, from atoms to populations of animals or people, to galaxies. Hence, a substance may be homgeneous on a larger scale, compared to being heterogenous on a smaller scale within the same substance. This is known as an effective medium approach, or effective medium approximations.

Heterogeneity

Heterogeneity is the the state of being heterogeneous. Pertaining to the sciences, it is a substance that is diverse in kind or nature; composed of diverse parts. Various disciplines understand heterogeneity, or as being heterogeneous in different ways. For example:

In mathematics heterogeneity occurs as incommensurable because of different kinds.

In physics it is understood as having more than one phase (solid, liquid, gas) present in a system or process.

In chemistry it means visibly consisting of different components.

With information technology it means a network comprising different types of computers, potentially with vastly differing memory sizes, processing power and even basic underlying architecture. Alternatively, a data resource with multiple types of formats.

Chemistry

A heterogeneous mixture is a mixture of two or more compounds. Examples are: mixtures of sand and water or sand and iron filings, a conglomerate rock, water and oil, a salad, trail mix, and concrete (not cement). During the sampling of heterogeneous mixtures of particles, the variance of the sampling error is generally non-zero. Gy's sampling theory quantitatively defines the heterogeneity of a particle as:

$h_{i}={\frac {(c_{i}-c_{\text{batch}})m_{i}}{c_{\text{batch}}m_{\text{aver}}}}.$

where $h_{i}$, $c_{i}$, $c_{\text{batch}}$, $m_{i}$, and $m_{\text{aver}}$ are respectively: the heterogeneity of the $i$th particle of the population, the mass concentration of the property of interest in the $i$th particle of the population, the mass concentration of the property of interest in the population, the mass of the $i$th particle in the population, and the average mass of a particle in the population.

Homogenization is the process of causing a heterogeneous mixture to become homogeneous, as is done with the making of homogenized milk.

Homogeneous and heterogeneous reactions

Homogeneous reactions are chemical reactions in which the reactants are in the same phase, while heterogeneous reactions have reactants in two or more phases. Reactions that take place on the surface of a catalyst of a different phase are also heterogeneous. A reaction between two gases, two liquids or two solids is homogeneous. A reaction between a gas and a liquid, a gas and a solid or a liquid and a solid is heterogeneous.

A mixture can be determined to be homogeneous when everything is settled and equal, and the liquid, gas, object is one color or the same form. Various models have been proposed to model the concentrations in different phases. The phenomena to be considered are mass rates and reaction rates. Surface area affects the reaction rate of heterogeneous reactions but not homogeneous reactions.

Biology

Genetic heterogeneity refers to multiple origins causing the same disorder in different individuals. Heterogeneity of ion channels means diversity of different types of channels serving a specific kind of current, e.g. by channels with different constitutive subunits.