6O2

6O2 denotes six units of diatomic oxygen, O2, in chemical notation. The coefficient 6 preceding O2 indicates six moles of oxygen gas participating in or produced by a reaction, corresponding to roughly 3.6 × 10^24 individual O2 molecules.

O2 is the diatomic molecule that makes up about 21% of Earth's atmosphere. It consists of two oxygen atoms bound together and is the most common allotrope of oxygen encountered in everyday chemistry. At room temperature it is a colorless, odorless gas. It has a molar mass of 32.00 g/mol, is paramagnetic, and its standard physical state is gas. Its melting point is very low (about −219°C) and its boiling point is about −183°C.

In chemical equations, the use of a coefficient such as 6 with O2 expresses a relative amount of oxygen gas rather than six discrete molecules. In practical terms, six moles of O2 are involved, which equates to roughly 3.6 × 10^24 molecules under standard conditions. A well-known example is photosynthesis, where the balanced equation shows six O2 molecules produced: 6 CO2 + 6 H2O → C6H12O6 + 6 O2.

Oxygen is essential for aerobic respiration in many organisms and is a common reactant in combustion and oxidation reactions. Safety considerations include the fact that concentrated oxygen supports combustion more vigorously, increasing fire hazards with flammable materials.

See also: Oxygen, Ozone, Oxidation.