2018 O Level Chem P1 Q17 — Energy Changes / Energy Profile Diagrams Solution
Question
When steam is passed through excess hot coke a reaction occurs and the coke cools. C(s) + H₂O(g) → CO(g) + H₂(g) The activation energy for the reaction is X. Which energy profile diagram for this reaction is correct?
Correct answer: C
Video Solution
Explanation
Answer: C. Because the coke cools, the surroundings lose heat to the reaction, so it is endothermic and \(\Delta H > 0\). On the energy profile the products must sit higher than the reactants, with a peak above both.
The activation energy X is always measured from the reactant level up to the top of the peak. Diagram C shows the reactants low on the left, a peak above them, the products at a higher level than the reactants, and X drawn from the reactant level to the peak.
Diagram A is exothermic (products lower than reactants). Diagram D is endothermic but draws X from the product level to the peak, which is wrong. Answer C.
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