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.

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Practical applications of heterogeneous reactions are in catalytic converts, fuel cells and chemical vapor deposition among others. Recently, manufacturing engineers have used surface reactions for synthesis of micro and nanoscale features in biomedical devices.

Likewise:

• Homogeneous mixture: Substance in which components are evenly mixed, (example: toothpaste, milk, perfume, steel, etc)
• Heterogeneous mixture: Substance in which components are not evenly mixed. (Don't blend together)

You can tell a mixture is homogeneous, when everything is settle and equal, the liquid, gas, object is one color or same form. Such as if you add objects or substances to another substance and it doesn't change.

There are various models which have been proposed over the years to model the concentrations in different phases. The phenomenon to be considered are mass transfer rates and reaction rates.