Question

Consider the following potential energy plots.

(a) Rank the reactions from fastest to slowest and explain the answer. If any reactions have equal rates, explain why.

(b) Label the reactions as endothermic or exothermic and support your answer.

(c) Rank the exothermic reactions from greatest to least change in potential energy and support your answer.

Short answer

(a) From fastest to slowest: 5,1 = 2, 4, 3

(b) Endothermic: 4; Exothermic: 1, 2, 3, 5.

(c) From greatest to least: 5 = 2, 1 = 3, 4 (positive)

Step-by-step solution

Understanding the fastest and slowest modes of reaction.

The fastest reaction is reaction 5 because its energy of activation is the lowest. After that, we have reactions 1 and 2 that are the same and a bit faster than reaction 4 which takes a bit longer to pass the ‘energy of activation saddle’. The slowest reaction of five is 3.

Identifying the exothermic and endothermic form of reaction.

Endothermic are all reactions for which the energy of product (s) is higher than the energy of reactant (s) and that is reaction 4. All others are exothermic.

Identifying the energy variation according to exothermic/endothermic reaction.

The potential energy of the system increases for endothermic reactions and decreases for exothermic reactions. The biggest amount of energy was released in reactions 5 and 2, then 1 and 3. Reaction 4 is endothermic.