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

Mar 4, 2017

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

#### Explanation:

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

$M g \left(s\right) + 2 H C l \left(a q\right) \rightarrow M g C {l}_{2} \left(a q\right) + {H}_{2} \left(g\right) \uparrow$

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:

$M g \rightarrow M {g}^{2 +} + 2 {e}^{-}$ $\left(i\right)$

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

${H}^{+} + {e}^{-} \rightarrow \frac{1}{2} {H}_{2} \left(g\right)$ $\left(i i\right)$

And we cross multiply to give $2 \times \left(i i\right) + \left(i\right)$:

$M g + 2 {H}^{+} \rightarrow M {g}^{2 +} + {H}_{2}$

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