C(s) + 2H2(g) CH4(g); H = -74.8 kJ mol-1. Which of the following diagrams gives an accurate representation of the above reaction? [R reactants; P products]
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Answer
(3) [figure]
Solution
∵ H = HP - HR = -74.8 kJ mol-1 (negative)
⇒ The reaction is exothermic: the products lie 74.8 kJ mol-1 below the reactants.
(1) P lies below R, but 74.8 is marked from R to the peak (activation energy), not between R and P.
(2) and (4) P lies above R (endothermic reaction).
(3) P lies below R and the gap between R and P is 74.8.
Answer: (3)