Hydrogen cyanide

Properties

General
Name	Hydrogen cyanide
Chemical formula	HCN
Appearance	Colourless liquid
Physical
Formula weight	27.0 amu
Melting point	260 K (-13 °C)
Boiling point	299 K (26 °C)
Density	0.7 ×103 kg/m3
Solubility	very soluble
Thermochemistry
ΔfH0gas	135.14 kJ/mol
ΔfH0liquid	109 kJ/mol
ΔfH0solid	100 kJ/mol
S0gas, 1 bar	201.82 J/mol·K
S0liquid, 1 bar	113.01 J/mol·K
S0solid	? J/mol·K
Safety
Ingestion	Extremely toxic. Early symptoms include nausea, vomiting and abdominal pain.
Inhalation	Extremely dangerous. Early symptoms include slow breathing rate, irritation.
Skin	Poisoning is thought to be possible through the skin.
Eyes	Dilated pupils are a symptom of poisoning.
More info	Hazardous Chemical Database (http://ull.chemistry.uakron.edu/erd/chemicals/7/6581)
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

Hydrogen cyanide (HCN), also known as formonitrile, is a colorless, volatile, and extremely poisonous chemical compound whose vapors have a bitter almond odor. It is produced in large quantities all over the world by the chemical industry where it is used in tempering steel, dyeing, explosives, engraving, the production of acrylic resin plastic, and other organic chemical products.

The carbon atom (C) is triple bonded to the nitrogen atom (N). The compound melts at -14°C and boils at 26°C. A simple way to produce the gas is by reduction of potassium ferrocyanide solution.

Hydrogen cyanide is weakly acidic and partly converts to the cyanide ion CN^– in solution. Such a solution is called prussic acid or hydrocyanic acid.

An HCN concentration of 300 parts per million of air will kill a human in a few minutes. The toxicity is caused by the cyanide ion. The mechanism of this toxicity, and the uses of the poison, are described on the cyanide page.