Chemistry
Chemistry
Problem
A beaker of ethanol is warmed from 20 °C to 40 °C. Which statement best accounts for the observed increase in the rate of evaporation in terms of the molecular speed distribution? a) Heating narrows the speed distribution, so collisions become less frequent and molecules leave more easily. b) Raising the temperature weakens hydrogen bonding so much that molecular speed becomes irrelevant; molecules escape mainly because intermolecular forces disappear. c) At the higher temperature, a larger fraction of molecules possess sufficient kinetic energy to overcome intermolecular attractions at the liquid surface. d) The total kinetic energy of every ethanol molecule doubles, allowing all molecules to escape the surface.Intuitive explanation
When you heat ethanol, you're adding kinetic energy to its molecules, shifting the entire speed distribution toward higher velocities. Evaporation depends on molecules having enough energy to escape the liquid surface—so as the distribution shifts right, more molecules exceed that escape-energy threshold. The key insight is that even a modest temperature increase can dramatically boost the fraction of molecules in the high-energy tail of the distribution, explaining why evaporation rate jumps noticeably.
Intuitive explanation
When you heat ethanol, you're adding kinetic energy to its molecules, shifting the entire speed distribution toward higher velocities. Evaporation depends on molecules having enough energy to escape the liquid surface—so as the distribution shifts right, more molecules exceed that escape-energy threshold. The key insight is that even a modest temperature increase can dramatically boost the fraction of molecules in the high-energy tail of the distribution, explaining why evaporation rate jumps noticeably.