How do you balance #Mg + HCl -> MgCl_2 + H_2#?

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Answer 1 · 2017-03-04T05:58:09

Garbage in must equal garbage out.......

For a simple redox reaction like this we could simply write:

#Mg(s) + 2HCl(aq) rarr MgCl_2(aq) + H_2(g)uarr#

Is this balanced stochiometrically? It must be if it is to represent chemical reality.

We could do it from first principles, i.e. the hydronium ion is a strong enuff oxidant to oxidize magnesium metal:

#Mg rarr Mg^(2+) + 2e^-# #(i)#

And of course the protium ion, the acidum or hydrogen ion, is reduced:

#H^(+) + e^(-) rarr 1/2H_2(g)# #(ii)#

And we cross multiply to give #2xx(ii) + (i)#:

#Mg +2H^(+) rarr Mg^(2+) + H_2#

The chloride ions are along for the ride, and do not participate in the redox transfer.