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
Enthalpy of atomization production of one mole of gaseous atoms. When the atoms in the molecule are different isotopes of the same element the calculation becomes non-trivial. Standard enthalpy of atomization is the enthalpy change when 1 mol of a substance is dissociated completely into atoms under standard conditions (298.15K, 1 bar). Enthalpy of atomization The enthalpy of atomization (also atomisation in British spelling) is the enthalpy change that accompanies the total separation of all atoms in a chemical substance (either a chemical element or a chemical compound). This is often represented by the symbol Δ"H" or Δ"H". All bonds in the compound