Question detail
In a practical experiment, a student adds a catalyst to a reaction mixture and notices that the reaction proceeds at the same rate as before, but the temperature of the mixture rises more slowly. Explain, using collision theory, why the presence of the catalyst does not change the overall reaction rate but affects the temperature change.
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At a glance
Question
Type
exam_style
Style
Topic
Rate of reaction
Question
In a practical experiment, a student adds a catalyst to a reaction mixture and notices that the reaction proceeds at the same rate as before, but the temperature of the mixture rises more slowly. Explain, using collision theory, why the presence of the catalyst does not change the overall reaction rate but affects the temperature change.
Answer
A catalyst provides an alternative reaction pathway with a lower activation energy, so more collisions have sufficient energy to react. However, the catalyst is not consumed in the reaction, so the total number of molecules reactingper unit time (the overall reaction rate) remains the same. Because the reaction proceeds more efficiently, less energy is released as heat per collision, resultingin a slower rise in temperature.
Explanation
The answer shows the student can apply collision theory to explain the role of a catalyst, distinguishingbetween activation energy, collision frequency, and the fact that catalysts are not consumed, while also linkingto observed temperature change.
Common mistake
Misattributing increased rate to more collisions only
Students often think that a higher concentration or temperature always speeds up a reaction simply because there are more collisions, ignoring that the collisions must also have sufficient energy.
Explain that collision theory requires both a higher collision frequency *and* a higher proportion of collisions with energy ≥ activation energy; students should describe how temperature raises particle speeds, increasing both frequency and the fraction of energetic collisions, and how concentration or pressure increases frequency but not necessarily energy per collision.
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