# How do you write an equation showing how HCl, which is a molecular substance and strong acid, could give ions when added to water?

$H C l \left(g\right) + {H}_{2} O \left(l\right) \rightarrow {H}_{3} {O}^{+} + C {l}^{-}$
As you say, hydrogen chloride is a room temperature gas; however, it is mighty soluble in water. And in water we conceive that it protonates the water molecular to give ${H}_{3} {O}^{+}$. $H C l$ PROTONATES the water solvent to form water-solvated hydronium ions and chloride ions......
${H}_{3} {O}^{+}$, the so-called hydronium ion, is our conception of a protonated water molecule. So far as anybody knows, it is a cluster of 2-4 water molecules with AN EXTRA ${H}^{+}$ incorporated in the cluster, i.e. ${H}_{5} {O}_{2}^{+}$ or ${H}_{7} {O}_{3}^{+}$. We call it ${H}_{3} {O}^{+}$ or even ${H}^{+}$ for convenience. The extra proton can rapidly move, or even tunnel if you like, from cluster to cluster.....