Homogeneity describes the equality of a property over the entire extent of a system, or the similarity of objects, phenomena, elements of a system. In chemistry, homogeneous substances are either homogeneous mixtures, also called solutions, for example alloys, or pure substances. The opposite of homogeneous substances are heterogeneous substances.
Heterogeneous mixtures of substances
The term heterogeneous also comes from the Greek and means different, whereby in physics and chemistry it means a system or mixture which comprises several phases. The phases that cannot be mixed with each other can be in the same state of aggregation (oil and water) or different (an aqueous solution over a hardly soluble precipitation).
Colloidal mixtures of substances
Often the individual phases are not so easy to distinguish macroscopically. The fact that milk, for example, is a phase mixture of an aqueous and a fat-like phase can only be recognized under the microscope. In such cases, we speak of colloidal systems (dispersions, emulsions, aerosols), i.e. phases that are particularly finely divided in a characteristic way.