What type of reaction is this: #HCN + NH_2^(-) rightleftharpoons CN^(-) + NH_3#?
This is an acid base reaction.
The base, amide ion, reacts with hydrogen cyanide, the acid, to give ammonia and cyanide anions. Amide ion is unstable in aqueous solution, and is normally formed by the addition of sodium or potassium metal to liquid ammonia, which is fairly easy to manipulate in a laboratory:
When a chunk of metal is added to the solvent, a deep blue colour rapidly develops, conceived to be due to a solvated electron that has a fairly long lifetime in ammonia. On standing, the electrons are conceived to couple, and give rise to a bronze colour.