Why do phase changes occur? 1. Compare: Set the Water temperature to 0 °C and click Play. Observe the water molecules.
Click Reset, set the Water temperature to 100 °C, and click Play again.
What do you notice? The water molecules are moving slightly faster at 100 °C than at 0 °C.
[Note: This difference may be too small to observe easily.]
2. Observe: Click Reset. The mean molecular speed of the water molecules is displayed
below the container. Set the Water temperature to 0 °C and Add/remove heat energy to
400 J/s. Click Play.
A. How does the mean speed of the water molecules change as they are heated?
The average speed of water molecules increases as they are heated.
B. Does the mean molecular speed change as much as the temperature as the
water heats up? Explain.
Sample For each degree of temperature change, the mean molecular
speed increases by about 1 m/s. At 100 °C, the mean molecular speed is about
17% faster than at 0 °C.
3. Explain: How is temperature related to the motions of molecules?
The higher the temperature, the faster the molecules move.
4. Observe: Click Reset. Set the Water temperature to 20 °C and the Ice volume to 50 cc.
Set Add/remove heat energy to 0 J/s. Click Play. How do the molecules in the liquid
interact with the molecules in the solid?
The molecules of the liquid collide with the molecules of solid, gradually breaking the bonds
between the molecules in the solid and causing the ice to melt.