What is the general trend for surface tension and viscosity as temperature rises?

• A. Both increase
• B. Both decrease
• C. Surface tension increases while viscosity decreases
• D. Surface tension decreases while viscosity increases

Answer: (B)

When temperature rises, molecules gain kinetic energy, which weakens intermolecular forces relative to thermal motion. That makes the surface less tightly bound, so surface tension decreases because less energy is needed to create new surface. At the same time, viscosity measures how strongly molecules resist flowing past each other. Higher temperature makes molecules move more vigorously and reduces the effective intermolecular interactions that hinder flow, so viscosity also decreases. Since both properties tend to drop as temperature increases for most liquids, the best description is that both decrease.