Question

consider the half reactions below for a chemical reaction.
mg → mg²⁺(aq) + 2e⁻
2h⁺(aq) + 2e⁻ → h₂(g)
what is the overall equation for this chemical reaction?
mg(s) + 2h⁺(aq) → mg²⁺(aq)+h₂(g)
mg(s) + 2h⁺(aq) → mg²⁺(aq)+2e⁻
mg²⁺(aq)+h₂(g) → mg(s) + 2h⁺(aq)
mg(s)+2h → mg(aq) + h₂(g)

Explanation:

Step1: Identify the oxidation and reduction half - reactions

The first reaction $Mg
ightarrow Mg^{2 +}(aq)+2e^{-}$ is an oxidation half - reaction (magnesium loses electrons). The second reaction $2H^{+}(aq)+2e^{-}
ightarrow H_{2}(g)$ is a reduction half - reaction (hydrogen ions gain electrons).

Step2: Combine the half - reactions

To get the overall reaction, we add the two half - reactions together. The electrons on the right side of the oxidation half - reaction and the left side of the reduction half - reaction cancel out. So, $Mg(s)+2H^{+}(aq)
ightarrow Mg^{2 +}(aq)+H_{2}(g)$.

Answer:

$Mg(s)+2H^{+}(aq)
ightarrow Mg^{2 +}(aq)+H_{2}(g)$ (corresponds to the first option in the multiple - choice)