define substance and mixture.

A chemical substance is a material with a definite chemical composition.A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. A pure chemical substance cannot be separated into other substances by a process that does not involve any chemical reaction and is rarely found in nature.

A  mixture is a substance made by combining two or more different materials without a chemical reaction occurring. A mixture is very different from a compound. The objects do not bond together in a mixture. A mixture can usually be separated back into its original components. Some examples of mixtures are: fruit salad,ocean water and soil