Question

in each figure, the dashed line represents the threshold kinetic energy required to vaporize the liquid. both substances are at the same temperature. which has an exothermic $delta_{vap}h$? substance a substance b a) substance a b) substance b c) both d) neither

Explanation:

Step1: Understand exothermic vaporization

Vaporization is endothermic in general. But here we consider relative ease of vaporization. A lower - energy requirement for vaporization implies stronger intermolecular forces initially. When these forces break during vaporization, more energy is absorbed.

Step2: Analyze the graphs

Substance A has a smaller fraction of molecules with kinetic energy above the threshold compared to substance B. This means substance A has stronger intermolecular forces. When substance A vaporizes, it will absorb more heat (more endothermic or less exothermic compared to B). Substance B has weaker intermolecular forces and is more likely to have a relatively more exothermic - appearing vaporization process in this context.

Answer:

B) substance B