An azeotrope is a mixture of two or more liquids that exhibits the same concentration in the vapor phase and the liquid phase/Physical_Properties_of_Matter/Solutions_and_Mixtures/Nonideal_Solutions/Azeotropes). This means that the component ratio of the unvaporized solution is equal to that of the vaporized solution, making it difficult to separate the components by distillation/Physical_Properties_of_Matter/Solutions_and_Mixtures/Nonideal_Solutions/Azeotropes). Azeotropes can either have a higher boiling point than either of the components or a lower boiling point/Physical_Properties_of_Matter/Solutions_and_Mixtures/Nonideal_Solutions/Azeotropes). When an azeotrope is boiled, the vapor has the same composition as the liquid. Azeotropes are useful in separating zeotropic mixtures. Combinations of solvents that do not form an azeotrope when mixed in any proportion are said to be zeotropic. Azeotropes consisting of two constituents are called binary azeotropes, while those consisting of three constituents are called ternary azeotropes/Physical_Properties_of_Matter/Solutions_and_Mixtures/Nonideal_Solutions/Azeotropes). Azeotropes of more than three constituents are also known.