# How do we use redox potentials to predict the reactivity of acids with metals?

May 8, 2016

Hydrochloric acid will oxidize zinc metal. It will not oxidize copper metal.

#### Explanation:

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

So how do you know? Well you turn to a handy redox potential:

$Z {n}^{2 +} + 2 {e}^{-} \rightarrow Z n \left(s\right)$ ; E^@=-0.76V

$C {u}^{2 +} + 2 {e}^{-} \rightarrow C u \left(s\right)$ ; E^@=+0.34V

${H}^{+} + {e}^{-} \rightarrow \frac{1}{2} {H}_{2} \left(g\right)$ ; E^@=+0.0V

Because, the reduction potential of zinc ion is negative, the oxidation reaction, the reverse reaction, has a positive E"^@ value., which is thermodynamically viable (i.e. $\Delta {G}^{\circ} = - n F {E}^{\circ}$).

According to this, hydrochloric acid should oxidize those metals whose redox potentials are negative.