A mole of any substance consists of Avogaro's number of the constituent entities of that substance. Entities are typically molecules but may also be atoms, ions, atomic particles, etc. Avogadro's number, approximately 6.02214×1023, makes the weight of a mole in grams equal to the weight of an entity in daltons. For example the molecular weight of the oxygen molecule O2 is 32 daltons whence a mole of oxygen weighs 32 grams. The hydrogen molecule H2 is much lighter at only 2 daltons, and a mole of hydrogen accordingly weighs only 2 grams. An important feature of the mole concept is that, despite this considerable difference in mass, a mole of oxygen and a mole of hydrogen have the same volume when at the same temperature and pressure. This remains essentially true for all gases no matter how simple or complex their constituent molecules, provided the molecules are significantly smaller than the intermolecular distances. A second important feature is that it rescales the individual molecules appearing in a theoretical equation up to units more convenient for laboratory use while preserving the numerical ratios of the participating reagents: if the equation shows 2 molecules of one reagent reacting with 4 molecules of another to produce 3 molecules, this scales up to 2 moles reacting with 4 moles to produce 3 moles.