Redox

Definition:

Redox reactions are chemical reactions involving the transfer of electrons between atoms or molecules.

Key Concepts:

• Oxidation: Loss of electrons
• Reduction: Gain of electrons
• Oxidizing Agent: Substance that causes oxidation (accepts electrons)
• Reducing Agent: Substance that causes reduction (donates electrons)

ALL REACTIONS EXCEPT DOUBLE REPLACEMENT CAN BE REDOX REACTIONS

Balancing Redox Equations:

Half-Reaction Method:

1. Identify the oxidized and reduced species.
2. Write half-reactions for oxidation and reduction.
3. Balance each half-reaction:
   • Add water to balance oxygen atoms.
   • Add hydrogen ions ( $ H^+ $ ) to balance hydrogen atoms.
   • Add electrons to balance charge.
4. Multiply the half-reactions by appropriate factors to balance the number of electrons transferred.
5. Add the balanced half-reactions to get the overall equation.

Example:

$$ \text{Zn} + \text{2HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 $$

Oxidation:

$$ \text{Zn} \rightarrow \text{Zn}^{2+} + 2\text{e}^- $$

Reduction:

$$ 2\text{H}^+ + 2\text{e}^- \rightarrow \text{H}_2 $$

Balanced Half-Reactions:

$$ \text{Zn} \rightarrow \text{Zn}^{2+} + 2\text{e}^- $$ ## $$ 2\text{H}^+ + 2\text{e}^- \rightarrow \text{H}_2 $$ Overall Equation:

$$ \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 $$