Homogeneity and heterogeneity are concepts relating to the uniformity in a substance. A material that is homogeneous is uniform in composition or character; one that is heterogeneous is distinctly nonuniform in one of these qualities.
The words homogeneous and heterogeneous come from Medieval Latinhomogeneus and heterogeneus, from Ancient Greek ὁμογενής (homogenēs) and ἑτερογενής (heterogenēs), from ὁμός (homos, “same”) and ἕτερος (heteros, “other, another, different”) respectively, followed by γένος (genos, “kind”); -ous is an adjectival suffix.
Heterogeneity is the state of being heterogeneous. It is the nature of opposition, or contrariety of qualities. It is diverse in kind or nature; composed of diverse parts, or resulting from differing causes. In general, a heterogeneous entity is composed of dissimilar parts, hence the constituents are of a different kind. The parts (or constituents) are connected, and of a conglomerate mass, and viewed in respect to the parts of which it is made up.
Various disciplines understand heterogeneity, or being heterogeneous, in different ways. For example:
In chemistry, a heterogeneous material consists of either or both of a) multiple states of matter or b) hydrophilic and hydrophobic substances in one mixture; an example of the latter would be a mixture of water, octane, and silicone grease.
In sociology it may refer to a society or group that includes individuals of differing ethnicities, cultural backgrounds, sexes, or ages.
Earth is a heterogeneous substance in many aspects. e.g. Rocks (geology) are inherently heterogeneous, usually occurring at the micro-scale and mini-scale. Subsequently, in studying ore bodies and mineral deposits, hydrocarbon accumulation and reservoir characterization, geoscientists always face heterogeneous and uncertain situation. Also in structural geology and many other earth-science fields, experts have to cope with heterogeneity in their investigations.
In medicine and genetics, a genetic or allelic heterogeneous condition is one where the same disease or condition can be caused, or contributed to, by several factors. In the case of genetics, varying different genes or alleles.
In cancer research, cancer cell heterogeneity is thought to be one of the underlying reasons that make treatment of cancer difficult.
In statistical meta-analysis, study heterogeneity is when multiple studies on an effect are actually measuring somewhat different effects due to differences in subject population, intervention, choice of analysis, experimental design, etc.; this can cause problems in attempts to summarize the meaning of the studies.
Homogeneity is the state of being homogeneous. Pertaining to the sciences, it is a substance where all the constituents are of the same nature; consisting of similar parts, or of elements of the like nature. For example, homogeneous particles, homogeneous elements, homogeneous principles, or homogeneous bodies; or (algebra) possessing the same number of factors of a given kind as with a homogeneous polynomial.
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:
, the heterogeneity of the th particle of the population
, the mass concentration of the property of interest in the th particle of the population
,the mass concentration of the property of interest in the population
, the mass of the th particle in the population
, 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 or two miscible liquids 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 .
^Heterogeneous Mixtures, in chemistry, is where certain elements are unwillingly combined and, when given the option, will separates completely. "Webster's Revised Unabridged Dictionary (1913 + 1828)" (Part of this paragraph is public domain material copyright 1828 and 1913). Heterogeneity. The ARTFL Project, University of Chicago. September 2010. Retrieved 2010-09-10.
^Heterogeneous Mixtures, in chemistry, is where certain elements are unwillingly combined and, when given the option, will separate. "Webster's Revised Unabridged Dictionary (1913 + 1828)" (Part of this paragraph is public domain material copyright 1828 and 1913). Heterogeneity. The ARTFL Project, University of Chicago. September 2010. Retrieved 2010-09-10.
^Bhatia, Sangeeta; John V Frangioni; Robert M Hoffman; A John Iafrate; Kornelia Polyak (10 July 2012). "The challenges posed by cancer heterogeneity". Nature Biotechnology30: 604–610. doi:10.1038/nbt.2294.
^Gamow, George (April 1967). "Chapter VI, "Descending Staircase"". One Two Three... Infinity (Mass market paperback) (Bantam Science and Mathematics, 5th printing ed.). Bantam. p. 117. [Clam chowder] represents a nice example of what is known as a heterogeneous material.|accessdate= requires |url= (help)
^Gy, P. (1979), Sampling of Particulate Materials: Theory and Practice, Elsevier: Amsterdam, 431 pp.