AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
Electrochemical cells can be used as a commercial source of electrical…
Full specification wording
Commercial applications of electrochemical cells (A-level only): Electrochemical cells can be used as a commercial source of electrical energy.
Any pair of half-cells with different electrode potentials can deliver electrical energy, and that is all a commercial cell is.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 1 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Any pair of half-cells with different electrode potentials can deliver electrical energy, and that is all a commercial cell is. The electrode with the more negative potential is the negative terminal, where oxidation releases electrons into the external circuit; the more positive electrode is where reduction takes them in. The EMF is fixed by the difference between the two electrode potentials, so making a cell physically larger does not raise its voltage. It raises how long the cell lasts, because there is more reactant. A non-rechargeable cell is finished when a reactant is used up. A rechargeable cell, such as a lithium-ion cell, has both electrode reactions driven backwards when an external voltage larger than its EMF is applied. Inside the cell, ions move through the electrolyte or porous separator; electrons never do.
What earns the marks
- Stating that the EMF equals the difference between the two electrode potentials.
- Identifying the negative electrode as the one where oxidation occurs.
- Stating that the electrolyte or porous separator allows ions to move so the circuit is complete.
- Distinguishing a rechargeable cell, whose reactions are reversed by an applied voltage, from a non-rechargeable one.
Common mistakes and how to put them right
Writing that the separator or electrolyte allows electrons to flow, which is not credited.
Calling the electrode at which oxidation happens the positive electrode.
Assuming a larger cell has a higher EMF rather than a greater capacity.
Saying a flat cell has 'run out of voltage' rather than run out of a reactant.
Exam tips
- Identify the negative electrode first by finding the more negative E⦵; everything else follows from that.
- Keep electron flow in the external wire and ion flow inside the cell strictly separate in your answer.
Try the lesson
The start of the Commercial applications of electrochemical cells (A-level only): Electrochemical cells can be used as a commercial source of electrical energy. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement describes a commercial advantage of using electrochemical cells, such as hydrogen fuel cells, rather than internal combustion engines to generate electrical energy?
Listen
Any pair of half-cells with different electrode potentials can deliver electrical energy, and that is all a commercial cell is. The electrode with the more negative potential is the negative terminal, where oxidation releases electrons into the external circuit; the more positive electrode is where reduction takes them in. The EMF is fixed by the difference between the two electrode potentials, so making a cell physically larger does not raise its voltage. It raises how long the cell lasts, because there is more reactant. A non-rechargeable cell is finished when a reactant is used up. A rechargeable cell, such as a lithium-ion cell, has both electrode reactions driven backwards when an external voltage larger than its EMF is applied. Inside the cell, ions move through the electrolyte or porous separator; electrons never do. A strong answer earns marks for these points. stating that the EMF equals the difference between the two electrode potentials. identifying the negative electrode as the one where oxidation occurs. stating that the electrolyte or porous separator allows ions to move so the circuit is complete. distinguishing a rechargeable cell, whose reactions are reversed by an applied voltage, from a non-rechargeable one. Exam tip: Identify the negative electrode first by finding the more negative E⦵; everything else follows from that.
Key words
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EMF
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cell polarity
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rechargeable cells
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ion movement in electrolyte
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See every definition
- EMF
- Fixed by the difference between the two electrode potentials, so making a cell physically larger does not raise it.
- cell polarity
- The electrode with the more negative potential is the negative terminal, where oxidation releases electrons into the external circuit.
- rechargeable cells
- Cells in which both electrode reactions are driven backwards when an external voltage larger than the EMF is applied.
- ion movement in electrolyte
- Inside the cell, ions move through the electrolyte or porous separator, so the circuit is complete; electrons never do.
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