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. Homogeneous and heterogeneous reactions Homogeneous reactions are chemical reactions in which the reactants and products 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. Geology Earth is a heterogeneous substance in many aspects; for instance, rocks (geology) are inherently heterogeneous, usually occurring at the micro-scale and mini-scale. Information technology With information technology, heterogeneous computing occurs in a network comprising different types of computers, potentially with vastly differing memory sizes, processing power and even basic underlying architecture. Mathematics and statistics In algebra, homogeneous polynomials have the same number of factors of a given kind. In the study of binary relations, a homogeneous relation R is on a single set (R ⊆ X × X) while a heterogeneous relation concerns possibly distinct sets (R ⊆ X × Y, X = Y or X ≠ Y). In statistical meta-analysis, study heterogeneity is when multiple studies on an effect are 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. Medicine 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, or in genetic terms, by varying or 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. Physics In physics, "heterogeneous" is understood to mean "having physical properties that vary within the medium". Sociology In sociology, "heterogeneous" may refer to a society or group that includes individuals of differing ethnicities, cultural backgrounds, sexes, or ages. Diverse is the more common synonym in the context. See also Complete spatial randomness Heterologous Epidemiology Spatial analysis Statistical hypothesis testing Homogeneity blockmodeling References External links The following cited pages in this book cover the meaning of "homogeneity" across disciplines . Chemical reactions Scientific terminology