This is an audio version of the Wikipedia Article:
00:01:20 1 Definition
00:04:24 2 History
00:06:13 3 Chemical elements
00:07:40 4 Chemical compounds
00:09:36 5 Substances versus mixtures
00:11:09 6 Chemicals versus chemical substances
00:14:19 7 Naming and indexing
00:16:27 8 Isolation, purification, characterization, and identification
00:16:54 9 See also
00:17:11 10 Notes and references
00:17:20 11 External links
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"There is only one good, knowledge, and one evil, ignorance."
A chemical substance is a form of matter having constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances, chemical compounds, or alloys. Chemical elements may or may not be included in the definition, depending on expert viewpoint.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, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical.
Chemical substances exist as solids, liquids, gases, or plasma, and may change between these phases of matter with changes in temperature or pressure. Chemical substances may be combined or converted to others by means of chemical reactions.
Forms of energy, such as light and heat, are not matter, and are thus not "substances" in this regard.