Question

section 3.3 assessment
reviewing concepts

1. name six common phase changes.
2. what happens to the temperature of a substance during a phase change?
3. how does the energy of a system change during a phase change?
4. what happens to the arrangement of water molecules as water melts and freezes?
5. what is the difference between evaporation and boiling?
6. explain why sublimation and deposition are classified as physical changes.

critical thinking

1. applying concepts how can the mass of a pile of snow decrease on a sunny day when the air temperature does not rise above 0°c?

Explanation:

Snow undergoes sublimation. Sublimation is a phase - change process where a solid directly turns into a gas without passing through the liquid phase. When snow (solid water) sublimes, water molecules escape from the solid snow into the air as water vapor. Since the mass of the snow is the mass of the water molecules in the solid state, as these molecules leave (sublime), the mass of the pile of snow decreases.

Answer:

The mass of the pile of snow decreases because the snow undergoes sublimation. In sublimation, solid water (snow) directly changes to water vapor (gas). As water molecules escape from the solid snow (in the form of vapor), the mass of the snow (which is composed of these water molecules in the solid state) reduces.