AQA · Chemistry · 8462
GCSE Chemistry (AQA): Reversible Reactions & Dynamic Equilibrium
Topic 6 — The Rate & Extent of Chemical Change. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Reversible Reactions & Dynamic Equilibrium (2027/28 exams)"; each card deep-links to the moment in the video it came from. Lesson 6.06 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_6.06.
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What does a double arrow (⇌) in a chemical equation indicate?
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The reaction is reversible — the products can react to reform the reactants.
Why is equilibrium described as dynamic rather than static?
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Both reactions are still happening — molecules keep breaking down and reforming — but at equal rates, so there is no overall change.
At equilibrium, are the concentrations of reactants and products equal to each other?
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No. They are constant, but one may be far greater than the other.
What colour change occurs when hydrated copper sulfate is heated?
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Blue crystals turn to white anhydrous copper sulfate powder as water is driven off.
What condition defines a reaction being at equilibrium?
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The forward and backward reactions occur at exactly the same rate, so concentrations of reactants and products stop changing.
Why is the forward reaction fastest at the very start of a reversible reaction?
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The concentration of reactants is at its highest and no products have formed yet, so the backward reaction has not started.
What does it mean if the position of equilibrium lies to the right?
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There are relatively more products than reactants in the equilibrium mixture.
What happens when water is added to white anhydrous copper sulfate?
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The backward (exothermic) reaction occurs, reforming blue hydrated copper sulfate crystals and releasing energy.
Is the thermal decomposition of hydrated copper sulfate endothermic or exothermic?
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Endothermic — it takes in heat energy from the surroundings to drive off the water.
Why can equilibrium never be reached in an open system?
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Reactants or products escape, so the backward reaction can never match the forward reaction and concentrations keep changing.
If the forward reaction of a reversible reaction is exothermic, what is the backward reaction?
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Endothermic — reversible reactions are always exothermic in one direction and endothermic in the other, transferring the same amount of energy.
In a reversible reaction, what is meant by the forward reaction?
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The reaction in which the reactants turn into the products (the top arrow of the double arrow).
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