Chapter 12 · Liquids, Solids, and Intermolecular Forces
12.3Intermolecular Forces in Action: Surface Tension and Viscosity
9 min · two checks
Predict
Why does honey pour more slowly than water?
The idea
- Define surface tension and viscosity.
- Predict how temperature affects viscosity.
Surface tension is the energy cost of making more surface. Liquids with strong intermolecular forces — water, because of hydrogen bonding — have high surface tension. Detergents lower water’s surface tension by crowding the surface with molecules that do not hydrogen-bond as effectively. That helps water spread and wet a fabric instead of beading.
Viscosity is resistance to flow. Strong attractions, long tangled molecules, and low temperature all raise it. Motor oils are graded because viscosity changes with temperature; a winter oil has to stay fluid when kinetic energy is low. Surface tension and viscosity are both macroscopic hints about the same invisible attractions.
Keep these
- High intermolecular forces → high surface tension.
- Viscosity is resistance to flow and falls as temperature rises.
- Surfactants lower surface tension.