In a physical change, the chemical composition of a substance remains the same. Some of the properties may be altered (such as shape, size, or state of matter) but the fundamental identity of the substance does not change. For example, if you melt ice, it changes from a solid to a liquid but it is still composed of H2O molecules. The chemical composition has not changed. Conversely, in a chemical change, the chemical composition of a substance is altered, resulting in the formation of new substances with different properties and compositions.