To determine which of the given equations describes a reduction, we need to analyze each reaction in terms of electron gain or loss.
A reduction reaction involves the gain of electrons, whereas an oxidation reaction involves the loss of electrons.
Let’s examine each equation:
1. [tex]\( \text{Mg} ( s ) \longrightarrow \text{Mg}^{2+} ( aq ) + 2e^{-} \)[/tex]
- In this reaction, magnesium (Mg) is changing from its elemental form (solid Mg) to a magnesium ion ([tex]\(\text{Mg}^{2+}\)[/tex]).
- To form [tex]\(\text{Mg}^{2+}\)[/tex], magnesium is losing 2 electrons.
- Since it is losing electrons, this is an oxidation reaction.
2. [tex]\( 2 \text{Cl} + 2e^{-} \longrightarrow 2 \text{Cl}^{-} \)[/tex]
- In this reaction, chlorine (Cl) atoms are changing to chloride ions ([tex]\(\text{Cl}^{-}\)[/tex]).
- Each chlorine atom gains an electron to become [tex]\(\text{Cl}^{-}\)[/tex], so 2 chlorine atoms gain a total of 2 electrons.
- Since it involves gaining electrons, this is a reduction reaction.
3. [tex]\( \text{Na} ( s ) \longrightarrow \text{Na}^ {+} ( aq ) + e^{-} \)[/tex]
- In this reaction, sodium (Na) is changing from its elemental form (solid Na) to a sodium ion ([tex]\(\text{Na}^{+}\)[/tex]).
- To form [tex]\(\text{Na}^{+}\)[/tex], sodium is losing 1 electron.
- Since it is losing an electron, this is an oxidation reaction.
4. [tex]\( \text{Al} (s) \longrightarrow \text{Al}^{3+} ( aq ) + 3e^{-} \)[/tex]
- In this reaction, aluminum (Al) is changing from its elemental form (solid Al) to an aluminum ion ([tex]\(\text{Al}^{3+}\)[/tex]).
- To form [tex]\(\text{Al}^{3+}\)[/tex], aluminum is losing 3 electrons.
- Since it is losing electrons, this is an oxidation reaction.
The equation that describes a reduction is the one that involves a gain of electrons. From the analysis above, the reaction that matches this criterion is:
[tex]\[ 2 \text{Cl} + 2e^{-} \longrightarrow 2 \text{Cl}^{-} \][/tex]
Therefore, the equation that describes a reduction is:
[tex]\[ 2 \text{Cl} + 2e^{-} \longrightarrow 2 \text{Cl}^{-} \][/tex]
