🔬 Chemical Reactions – Redox
What is a Redox Reaction?
A redox (reduction‑oxidation) reaction is a chemical change where electrons are transferred between substances. One reactant loses electrons (oxidised) and another gains electrons (reduced).
Think of it like a game of “give‑and‑take”:
- 🧑🔬 Oxidation – the player who gives away electrons.
- 🧑🔬 Reduction – the player who receives electrons.
Oxidation Numbers – The Quick Check
Oxidation numbers (ON) help us spot who’s losing or gaining electrons.
- Assign the ON to each element in the reaction.
- Compare the ON of each element in reactants vs. products.
- Change in ON tells you oxidation or reduction.
Rule of thumb: Higher ON → Oxidised, Lower ON → Reduced.
Step‑by‑Step: Identify Oxidation & Reduction
- Write the balanced equation.
- Assign oxidation numbers.
- Spot changes.
- Label the species:
- Oxidised species: ↑ ON
- Reduced species: ↓ ON
Example Reaction
| Reactant | Product | Oxidation Number Change |
|---|
| \$\ce{Zn}\$ | \$\ce{Zn^{2+}}\$ | \$0 \rightarrow +2\$ (Oxidised) |
| \$\ce{Cu^{2+}}\$ | \$\ce{Cu}\$ | \$+2 \rightarrow 0\$ (Reduced) |
Equation: \$\ce{Zn + Cu^{2+} -> Zn^{2+} + Cu}\$
Exam Tips 📚
- Always balance the equation first before assigning oxidation numbers.
- Check that the total charge on each side is the same.
- Remember: Oxidation = loss of electrons, Reduction = gain of electrons.
- Use the “give‑and‑take” analogy to explain quickly in your answer.
- When in doubt, write the half‑reactions – it clarifies the electron flow.