To determine which of the half-reactions represents reduction in the given chemical equation, we need to identify which of the processes involve a gain of electrons.
Reduction is the process of gaining electrons, whereas oxidation is the process of losing electrons.
Given chemical reaction:
[tex]$
Zn (s) + 2 H^{+}(aq) \rightarrow Zn^{2+}(aq) + H_2(g)
$[/tex]
Let's look at the provided half-reactions:
1. [tex]\( \text{Zn} (s) \rightarrow \text{Zn}^{2+}(aq) + 2 e^{-} \)[/tex]
2. [tex]\( 2 H^{+}(aq) + 2 e^{-} \rightarrow H_2(g) \)[/tex]
3. [tex]\( \text{Zn} (s) \rightarrow \text{Zn}^{2+}(aq) + e^{-} \)[/tex]
4. [tex]\( 2 H^{+}(aq) + e^{-} \rightarrow H_2(g) \)[/tex]
To identify the reduction half-reaction, we must check which reaction involves the gain of electrons.
1. In the reaction [tex]\( \text{Zn} (s) \rightarrow \text{Zn}^{2+}(aq) + 2 e^{-} \)[/tex], zinc is losing electrons (oxidation).
2. In the reaction [tex]\( 2 H^{+}(aq) + 2 e^{-} \rightarrow H_2(g) \)[/tex], the hydrogen ions ([tex]\(H^{+}\)[/tex]) are gaining electrons to form hydrogen gas (reduction).
3. In the reaction [tex]\( \text{Zn} (s) \rightarrow \text{Zn}^{2+}(aq) + e^{-} \)[/tex], zinc is again losing electrons (oxidation).
4. In the reaction [tex]\( 2 H^{+}(aq) + e^{-} \rightarrow H_2(g) \)[/tex], once again, hydrogen ions ([tex]\(H^{+}\)[/tex]) are gaining electrons (but the stoichiometry doesn't match the given reaction).
Among these, the correct half-reaction that represents a reduction process (gain of electrons) and matches the stoichiometry of the given equation is:
[tex]\( 2 H^{+}(aq) + 2 e^{-} \rightarrow H_2(g) \)[/tex]
Therefore, the correct half-reaction representing reduction is:
[tex]\( 2 H^{+}(aq) + 2 e^{-} \rightarrow H_2(g) \)[/tex]
Hence, the second half-reaction correctly represents reduction for this equation.
