| Appearance | colorless, odorless and tasteless gas. |
|---|---|
| Production | CO carbon monoxide is produced from the partial oxidation of carbon-containing compounds; it forms when there is not enough oxygen to produce CO2 carbon dioxide. |
| CO | N2 | O2 | Air | |
|---|---|---|---|---|
| boiling point | 82 K | 77 K | 90.20 K | |
| melting point | 68 K | 63 K | 54.36 K | |
| bond dissociation energy | 1072 kJ/mol | 942 kJ/mol | 498 | |
| Molar mass | 28 | 28,8 | ||
| Solubility in water | 26 mg/L (20 °C) | 7,6 mg/L (20 °C) | ||
| Bond length | 112.8 pm between C & O | 121 |
According to the ideal gas law, CO is less dense than air. Neither gas is "ideal", however, so the exact densities and other comparative values depend upon temperature and pressure.
The bond dissociation energy of 1072 kJ/mol represents the strongest chemical bond known.
Oxygen is more soluble in water than nitrogen is; water contains approximately 1 molecule of O2 for every 2 molecules of N2, compared to an atmospheric ratio of approximately 1:4. The solubility of oxygen in water is temperature-dependent, and about twice as much (14.6 mg·L−1) dissolves at 0 °C than at 20 °C (7.6 mg·L−1).
Self-ionization of water 2H2O → H3O+ + OH- is a disproportionation but not a redox reaction.
The disproportionation of hydrogen peroxide into water and oxygen catalysed by either potassium iodide or the enzyme catalase:
2H2O2 → 2H2O + O2
The Boudouard reaction is the redox reaction of a chemical equilibrium mixture of carbon monoxide and carbon dioxide at a given temperature. It is the disproportionation of carbon monoxide into carbon dioxide and graphite or its reverse:
While formation enthalpy of CO2 is higher than that of CO, the formation entropy is much lower. Consequently, according to the Ellingham diagram, the overall free energy change of formation of CO2 by oxidation of carbon is almost constant and indifferent of the temperature, while the free energy change of formation of CO is a decreasing line. These two lines meet at 700℃, so the Boudouard reaction implies that on lower temperatures the equilibrium is on the exothermic carbon dioxide side and on higher temperatures the endothermic formation of carbon monoxide is the dominant reaction.
For instance, in the high temperature reducing environment of a smokestack, carbon monoxide is the stable product. When the carbon monoxide reaches the top of the smokestack, and the cooler air, the Boudouard Reaction takes place; the carbon monoxide is oxidized into carbon dioxide, and the graphite precipitates (reduces) as soot. The Ellingham diagram is a plot of the Gibbs free energy change for a reaction (ΔG), versus temperature.
In industrial catalysis, this is not just an eyesore; the coking can cause irreversible damage to catalysts and catalyst beds. This reaction also takes place in blast furnaces where carbon monoxide is used as the reductive agent on purifying metallic iron from its oxides in ore.
The reaction is named after the French chemist, Octave Leopold Boudouard (1872—1923) who investigated this equilibrium in 1905.