Battery or Electrolysis?
Same equipment. Same chemicals.
This is one of those topics that looks simple, uses familiar kit, and yet consistently trips students up.
Two electrodes.
An electrolyte.
Wires, ions, electrons…
So why does one produce electricity, while the other needs electricity to work?
Let’s untangle it properly.
The core idea (the bit students miss)
A battery uses a spontaneous chemical reaction to make electricity.
Electrolysis uses electricity to force a non-spontaneous chemical reaction.
That single sentence is the key. Everything else flows from it.
1. What’s happening in a battery (galvanic cell)?
In a battery:
The redox reaction is energetically favourable
Electrons are released naturally at the negative electrode
Those electrons flow through the external circuit
Electrical energy is produced as a by-product of chemistry
In student language:
The chemicals want to react, and we steal the electrons as they do so.
Oxidation happens at the negative electrode
Reduction happens at the positive electrode
And crucially:
⚡ The battery is the power supply
2. What’s happening in electrolysis?
In electrolysis:
The reaction is not energetically favourable
Nothing will happen on its own
An external power supply pushes electrons around
Electrical energy is consumed to make chemistry happen
In student language:
The reaction doesn’t want to happen, so we force it.
Oxidation happens at the positive electrode
Reduction happens at the negative electrode
And this is the mental flip that causes confusion:
🔌 The power supply is doing the hard work, not the chemicals
3. Why students get confused
Because almost everything looks the same.
| Feature | Battery | Electrolysis |
|---|---|---|
| Electrodes | ✔ | ✔ |
| Electrolyte | ✔ | ✔ |
| Redox reactions | ✔ | ✔ |
| Electrons flowing | ✔ | ✔ |
But the direction of cause and effect is reversed.
Battery: chemistry → electricity
Electrolysis: electricity → chemistry
Students often memorise:
“OIL RIG”
…but forget to ask why the electrons are moving in the first place.
4. The sign of the electrodes (the exam trap)
This is where marks are lost.
In a battery:
Negative electrode = oxidation
Positive electrode = reduction
In electrolysis:
Positive electrode = oxidation
Negative electrode = reduction
Same words.
Opposite signs.
Different reason.
👉 The sign depends on who is pushing the electrons.
5. The one question I ask students in lessons
“If I unplug the power supply, does the reaction still happen?”
If yes → it’s a battery
If no → it’s electrolysis
That single question clears more confusion than a page of notes.
Why this matters beyond exams
Understanding this difference helps students later with:
Fuel cells
Rechargeable batteries
Corrosion and rust prevention
Electroplating and metal extraction
Redox chemistry in biology and industry
It’s not just an exam trick – it’s foundational chemistry thinking.
Want to see this done for real?
At Hemel Private Tuition, we run both setups side-by-side in the lab, measure voltages and currents live, and deliberately “break” the circuits so students can see what stops and what keeps going.
It’s one of those moments where chemistry suddenly makes sense.
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