Understanding Molecular Motion
Molecules are constantly in motion. This motion can be in the form of:
* Translation: Moving from one place to another.
* Rotation: Spinning around an axis.
* Vibration: Atoms within the molecule moving back and forth relative to each other.
Let's consider some observations:
* A. Diffusion of perfume in a room: This is a clear example of translation. Perfume molecules spread out, moving from areas of high concentration to low concentration.
* B. Expansion of a balloon when heated: This is due to increased translational motion of the gas molecules inside the balloon. As they move faster, they collide with the balloon walls more frequently and with more force, causing it to expand.
* C. Condensation of steam on a cold surface: This is a change of state, not directly demonstrating molecular motion. Condensation is the result of molecules slowing down and coming closer together due to a decrease in temperature, not a specific type of molecular motion.
* D. Brownian motion of pollen grains in water: This is a direct observation of translation. The pollen grains are bombarded by the water molecules, causing them to jiggle randomly.
Answer:
The observation that does not show molecular motion is C. Condensation of steam on a cold surface.
Why? While condensation is a result of molecular interactions, it's not directly demonstrating the types of motion that molecules undergo.
