3.2.7—Secondary (rechargeable) cells
- Syllabus
- First assessment 2025
- Objective
- 3.2.7
- Level
- HL
Primary, Secondary and Fuel Cells
| Cell | Energy direction | Reuse |
|---|---|---|
| primary | chemical → electrical | not readily reversible |
| secondary | chemical ⇌ electrical | recharge by external power |
| fuel | chemical → electrical while reactants are supplied | refill fuel |
Write the discharge half-equations first. Charging a secondary cell requires an external potential to drive their reverse, whereas a primary cell is not designed for safe efficient reversal and a fuel cell continues only while reactants are supplied. Rechargeability is a reaction-design property, not simply the presence of a power socket.
Explaining Rechargeability
Assessment in practice
Representative question
Question 1
[Maximum number: 1]
Outline how a rechargeable battery differs from a primary cell.
«redox» reaction in rechargeable battery is reversible «but not in a primary cell» OR
rechargeable battery needs to be charged before use
OR
rechargeable battery has greater rate of self-discharge
Marking guidance:
Accept "rechargeable battery can be
recharged AND primary cell cannot"
OR "rechargeable battery can be used
more than once/many times AND
primary cell can be used once only".
Electron Transfer Reactions Summary
Retrieve the route: assign oxidation states, balance half-equations, predict displacement, label cells, trace electrons and ions, follow organic redox pathways, calculate potentials and choose electrolysis products.
Check electron loss/gain, anode/cathode versus polarity, spontaneous sign, salt-bridge direction, ions present, organic functional-group direction and object-cathode placement.