AQA · GCSE · Chemistry

    Course version: 8462 · Version from Sept 2018

    The fuel is oxidised electrochemically within the fuel cell to produce a…

    Full specification wording

    Fuel cells: The fuel is oxidised electrochemically within the fuel cell to produce a potential difference.

    Inside a fuel cell, the fuel is oxidised at an electrode in an electrochemical reaction.

    Checked against the AQA 8462 specification (opens in a new tab) on .

    • Point 2 of 5
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Inside a fuel cell, the fuel is oxidised at an electrode in an electrochemical reaction. Oxidation means the fuel loses electrons, and these electrons flow through an external circuit, creating a potential difference that can drive a current. In a hydrogen fuel cell, hydrogen is oxidised at the negative electrode, releasing electrons that travel through the external circuit to the positive electrode, where oxygen is reduced. The key idea is that the oxidation is electrochemical: it happens at an electrode surface and transfers electrons through the circuit rather than releasing energy only as heat.

    For example: Hydrogen molecules are oxidised to hydrogen ions and electrons at one electrode, and the electron flow does electrical work in the external circuit.

    What earns the marks

    • The fuel undergoes oxidation at an electrode within the fuel cell.
    • Oxidation involves the loss of electrons from the fuel.
    • The electrons flow through an external circuit, producing a potential difference.
    • The electrochemical oxidation occurs at an electrode surface rather than by simple burning.
    • The potential difference drives a current that can do useful work.

    Common mistakes and how to put them right

    • Describing the fuel as burning in the fuel cell.

      Put it right by explaining that the fuel is oxidised electrochemically at an electrode.

    • Saying that oxidation is gain of electrons.

      Put it right by stating that oxidation is loss of electrons.

    • Claiming that the potential difference is produced without any electron transfer.

      Put it right by linking the electron flow through the external circuit to the potential difference.

    Exam tips

    • Use the term electrochemical to show that the oxidation occurs at an electrode and transfers electrons.
    • Link oxidation of the fuel to electron loss and then to electron flow in the external circuit.
    • Avoid saying the fuel burns; describe oxidation at the electrode instead.

    Try the lesson

    The start of the Fuel cells: The fuel is oxidised electrochemically within the fuel cell to produce a potential difference. lesson, made from checked teaching notes for this specification point.

    Have a go first

    In a hydrogen fuel cell, what happens to the hydrogen fuel to produce a potential difference?

    Listen

    Inside a fuel cell, the fuel is oxidised at an electrode in an electrochemical reaction. Oxidation means the fuel loses electrons, and these electrons flow through an external circuit, creating a potential difference that can drive a current. In a hydrogen fuel cell, hydrogen is oxidised at the negative electrode, releasing electrons that travel through the external circuit to the positive electrode, where oxygen is reduced. The key idea is that the oxidation is electrochemical: it happens at an electrode surface and transfers electrons through the circuit rather than releasing energy only as heat. For example, hydrogen molecules are oxidised to hydrogen ions and electrons at one electrode, and the electron flow does electrical work in the external circuit. A strong answer earns marks for these points. The fuel undergoes oxidation at an electrode within the fuel cell. Oxidation involves the loss of electrons from the fuel. The electrons flow through an external circuit, producing a potential difference. The electrochemical oxidation occurs at an electrode surface rather than by simple burning. A common slip: Describing the fuel as burning in the fuel cell. Instead, explaining that the fuel is oxidised electrochemically at an electrode. Exam tip: Use the term electrochemical to show that the oxidation occurs at an electrode and transfers electrons.

    See it

    A top-to-bottom flowchart with six boxes joined by arrows. The first box says the fuel enters the fuel cell and points to the second, which says the fuel is oxidised electrochemically at an electrode. This points to the third box, stating that oxidation means the fuel loses electrons. The third points to the fourth, saying electrons flow through an external circuit. The fourth points to the fifth, saying a potential difference is produced, and the fifth points to the final box, saying the potential difference drives a current that can do useful work.
    It shows the sequence from fuel being oxidised electrochemically at an electrode, through electron loss and electron flow in an external circuit, to a potential difference that drives a current.

    Put it in order

    Put these steps in the order they happen.

    1. 1. Oxidation: fuel loses electrons
    2. 2. Fuel is oxidised electrochemically at an electrode
    3. 3. Fuel enters the fuel cell
    4. 4. The potential difference drives a current that can do useful work
    5. 5. A potential difference is produced
    6. 6. Electrons flow through an external circuit

    Key words

    Say what each word means before you turn the card.

    Electrochemical oxidation

    Try answering aloud or in your head before turning the card.

    Electron transfer

    Try answering aloud or in your head before turning the card.

    Potential difference

    Try answering aloud or in your head before turning the card.

    Electrodes

    Try answering aloud or in your head before turning the card.

    See every definition
    Electrochemical oxidation
    The fuel is oxidised at an electrode surface, transferring electrons through the circuit rather than releasing energy only as heat.
    Electron transfer
    Oxidation involves the loss of electrons from the fuel, and these electrons flow through an external circuit.
    Potential difference
    Produced by the flow of electrons through an external circuit, it can drive a current that can do useful work.
    Electrodes
    The places where oxidation and reduction happen, with hydrogen oxidised at the negative electrode and oxygen reduced at the positive electrode.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-to-bottom flowchart with six boxes joined by arrows. The first box says the fuel enters the fuel cell and points to the second, which says the fuel is oxidised electrochemically at an electrode. This points to the third box, stating that oxidation means the fuel loses electrons. The third points to the fourth, saying electrons flow through an external circuit. The fourth points to the fifth, saying a potential difference is produced, and the fifth points to the final box, saying the potential difference drives a current that can do useful work.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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