What gas involved during the reaction between zinc and hydrochloric acid? I know it's hydrogen, but why?
In the activity series (see link below) Zn is above hydrogen; therefore, Zn will replace H^+.
Zn + 2HCl ==> H2 + ZnCl2.
http://www.files.chem.vt.edu/RVGS/ACT/notes/activity_series.html