How does hydrogen chloride differ from hydrochloric acid?

1 Answer
Truong-Son N. · P dilip_k
Apr 9, 2016

They're almost the same thing.

At STP, hydrogen chloride is a colorless gas, and it condenses below #-85^@ "C"#. It can be dissolved into a solvent like water to give you hydrochloric acid. That is, hydrochloric acid is an aqueous solution of hydrogen chloride.

But they both have the chemical formula #"HCl"#. So if you want to differentiate between them, add the phase. #"HCl"(aq)# is hydrochloric acid, while #"HCl"(g)# is hydrogen chloride.

In addition we can say that hydrogen chloride, i.e.#"HCl"(g)#, exists in a molecular state where as hydrochloric acid ionizes to form #"H"_3"O"^(+)# (hydronium ion) and #"Cl"^(-)# (chloride ion) while interacting with water molecules:

#"H"_2"O"(l) + "HCl"(g) rightleftharpoons "H"_3"O"^(+)(aq) + "Cl"^(-)(aq)#

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