Chemical substance 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
Organic compound substance in Martian soil. Terrestrially, it, and its anhydride, mellitic anhydride, are associated with the mineral mellite (AlC(COO)·16HO). A slightly broader definition of organic compound includes all compounds bearing C-H or C-C bonds. This would still exclude urea. Moreover, this definition still leads to somewhat arbitrary divisions in sets of carbon-halogen compounds. For example, CF and CCl would be considered by this rule to be "inorganic", whereas CFH and CHCl would be organic, though these compounds share many physical and chemical properties. Organic compounds may be classified in a variety of ways. One major distinction is between natural and synthetic