IB Understanding
Definition of Electrolysis
Electrolysis is the passage of direct electric current through an electrolyte (molten salt or aqueous solution) driving a non-spontaneous redox reaction (\(\Delta G > 0\)).
Electrolysis Cell
Voltaic Cell vs Electrolytic Cell
| Feature | Voltaic Cell | Electrolytic Cell |
|---|---|---|
| Reaction type | Spontaneous | Non-spontaneous |
| Energy conversion | Chemical → Electrical | Electrical → Chemical |
| Anode charge | Negative (−) | Positive (+) |
| Cathode charge | Positive (+) | Negative (−) |
| Salt bridge | Present | Not needed (one container) |
Predicting Products (Aqueous Solutions)
Electrode Reaction
Cathode Reduction (Negative Electrode)
At the cathode (−), reduction occurs:
\[\text{Metal cations or } \text{H}^+ / \text{H}_2\text{O} \text{ gain electrons: } 2\text{H}^+(\text{aq}) + 2\text{e}^- \rightarrow \text{H}_2(\text{g})\]
Electrode Reaction
Anode Oxidation (Positive Electrode)
At the anode (+), oxidation occurs:
\[\text{Halide anions or } \text{H}_2\text{O} \text{ lose electrons: } 2\text{Cl}^-(\text{aq}) \rightarrow \text{Cl}_2(\text{g}) + 2\text{e}^-\]
Exam Tip
The PANIC Mnemonic for Electrolysis
PANIC Mnemonic: Positive Anode, Negative Is Cathode (applies to electrolytic cells only!).
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