What is the difference between hcl acid and hcl gas?
HCl gas is molecular HCl in the gaseous phase, HCl acid is HCl in solution with water, and can be said to be in the form H+ Cl-. (Or to be a pendant, H3O+ Cl- as techincally protons do not exist on their own in solution.) It is this dissociation of the molecule into constituent ions which gives an acid its properties. On a physical level, HCl gas is a yellow/green gas, and HCl acid is a clear solution.