In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. It can be solid, liquid or gas.
Chemical substances are often called 'pure' to set them apart from mixtures. 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. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, simple or seemingly pure substances found in nature can in fact be mixtures of chemical substances. For example, tap water may contain small amounts of dissolved sodium chloride and compounds containing iron, calcium and many other chemical substances.
Chemical substances exist as solids, liquids, gases, or plasma and may change between these phases of matter with changes in temperature or pressure. Chemical reactions convert one chemical substance into another.
Forms of energy, such as light and heat, are not considered to be matter, and thus they are not "substances" in this regard.
Read more about Chemical Substance: Definition, History, Chemical Elements, Chemical Compounds, Substances Versus Mixtures, Chemicals Versus Chemical Substances, Naming and Indexing, Isolation, Purification, Characterization, and Identification
Famous quotes containing the words chemical and/or substance:
“If Thought is capable of being classed with Electricity, or Will with chemical affinity, as a mode of motion, it seems necessary to fall at once under the second law of thermodynamics as one of the energies which most easily degrades itself, and, if not carefully guarded, returns bodily to the cheaper form called Heat. Of all possible theories, this is likely to prove the most fatal to Professors of History.”
—Henry Brooks Adams (1838–1918)
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—Henry David Thoreau (1817–1862)