Re: Why does copper react with HCl even those is below H on the act.series?seri

I asked my colleague, Professor Emory Howell, a better inorganic chemist 
than I for asssistance:


Even though hydrochloric acid is not strongly oxidizing, at elevated
temperatures copper(I) ions and dihydrogen gas are produced.

2 Cu(s) + 2H+(aq) = 2 Cu+(aq) + H2(g)

a second reaction occurs, which has a very large equilibrium constant

Cu+(aq) + 2Cl-(aq) = [CuCl2]-(aq)

The reaction of Zn(s) with HCl is sufficiently exothermic to start the
first reaction but it the second reaction provides the driving force to
completely oxidize the copper. If one wants to have "floating" pennies they
need to be removed from the HCl solution and placed in water as soon as the
Zn oxidation appears to be complete.

The above explanation does not explain the blue color, however. It only
occurs upon standing because Cu+(aq) disproportionates:

2 Cu+(aq) = Cu2+(aq) +Cu(s)

The [CuCl2]- complex ions provide resevoir of Cu+ ions as the relatively
slower disproportionation takes place.

Any one who removes the "floating" pennies immediately from the HCl misses
this fascinating interplay of thermodynamic and kinetic factors.
Congratulations to your correspondent for observing it.


J. Emory Howell
Professor                                      		 High School Editor
Department of Chemistry and Biochemistry      Journal of Chemical Education