Hydrogen bond
Hydrogen bonds can vary in strength from weak (1–2 kJ mol) to strong (161.5 kJ mol in the ion ). Typical enthalpies in vapor include:
Hydrochloric acid
As a strong acid, hydrogen chloride has a large "K". Theoretical attempts to assign the p"K" of hydrogen chloride have been made, with the most recent estimate being −5.9. However, it is important to distinguish between hydrogen chloride gas and hydrochloric acid. Due to the leveling effect, except when highly concentrated and behavior deviates from ideality, "hydrochloric acid" (aqueous HCl) is only as acidic as the strongest proton donor available in water, the aquated proton (popularly known as "hydronium ion"). When chloride salts such as NaCl are added to aqueous HCl, they have only a minor effect on pH, indicating that Cl is a very weak conjugate base and that HCl is fully dissociated in aqueous solution. Dilute solutions of HCl have a pH close to that predicted by assuming full dissociation into hydrated H and Cl.