How would Figure 2 be different if no catalyst was used?

Answer options:

The final energy level would be higher.

The final energy level would be lower.

The line would reach a higher peak.

The line would reach a lower peak.

How to approach this question

Consider the function of a catalyst. A catalyst speeds up a reaction by providing an alternative pathway with a lower activation energy. The question asks what would happen if the catalyst was *not* used. 1. How would the activation energy change without a catalyst? 2. How is activation energy represented on the reaction profile? 3. Does a catalyst affect the energy of the reactants or products (the start and end points)?

Full Answer

C.The line would reach a higher peak.✓ Correct

The correct answer is "The line would reach a higher peak". A catalyst provides an alternative reaction pathway with a lower activation energy, so without a catalyst, the activation energy would be higher.

A catalyst increases the rate of a chemical reaction without being used up in the process. It does this by providing an alternative reaction pathway that has a lower activation energy. The activation energy is represented by the peak of the curve on a reaction profile. The diagram shows the catalysed reaction, which has a relatively low peak. If no catalyst were used, the reaction would still happen, but it would follow a pathway with a higher activation energy. This means the peak of the curve would be higher. Importantly, a catalyst does not change the energy of the reactants or the products, so the starting and ending energy levels of the profile would be exactly the same.

Common mistakes

✗ Thinking the catalyst changes the overall energy change (enthalpy change). ✗ Confusing the effect of adding a catalyst with removing one.

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Practice the full AQA GCSE Chemistry Higher Tier Paper 2

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