AQA · Chemistry · 8462
GCSE Chemistry: Representation of reactions at electrodes as half equations
Chemical changes · AQA GCSE Chemistry (8462), specification point 4.4.3.5. Cards are generated from the exam board's own specification for "Representation of reactions at electrodes as half equations", and every card links back to the page it came from. Higher tier only. Specification © AQA — used with attribution.
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During electrolysis, what type of reaction occurs at the cathode?
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Reduction — positively charged ions gain electrons.
During electrolysis, what type of reaction occurs at the anode?
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Oxidation — negatively charged ions lose electrons.
In electrolysis, the cathode is the ? electrode.
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negative
In electrolysis, the anode is the ? electrode.
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positive
Write the half equation for hydrogen forming at the cathode during electrolysis.
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2H⁺ + 2e⁻ → H₂
Write the half equation for oxygen forming from hydroxide ions at the anode.
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4OH⁻ → O₂ + 2H₂O + 4e⁻ (equivalently 4OH⁻ − 4e⁻ → O₂ + 2H₂O)
Why is the reaction at the cathode classed as a reduction?
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Positive ions gain electrons there, and gain of electrons is reduction.
What is a half equation in electrolysis?
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An equation showing the reaction at one electrode, including the electrons gained or lost.
What is an exothermic reaction?
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A reaction that releases energy to the surroundings.
What is an endothermic reaction?
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A reaction that takes in thermal energy from the surroundings.
Energy changes in chemical reactions arise from the breaking and formation of ?.
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bonds
Why is electrolysis useful for producing certain elements?
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It can decompose ionic substances to extract elements that are too expensive to extract any other way.
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