When hydrogen cyanide (HCN) is dissolved in water, it undergoes a chemical reaction with water molecules to form hydrocyanic acid (HCN(aq)) and hydroxide ions (OH-) according to the following equilibrium equation:

HCN(aq) + H2O(l) <=> H3O+(aq) + CN-(aq)

In this equilibrium, the species with the highest concentration is water (H2O). Water is the solvent in this system, and it is present in much greater concentration compared to the other species. The concentration of water remains nearly constant throughout the reaction.

The concentrations of HCN(aq), H3O+(aq), and CN-(aq) are relatively low compared to the concentration of water. The equilibrium constant for this reaction is very small, indicating that the reaction proceeds to a limited extent. Therefore, the majority of the HCN molecules remain unreacted and dissolved in the water.