Question

student exploration: phase changes
vocabulary: altitude, boil, boiling point, freeze, freezing point, gas, liquid, melt, melting point, phase, solid
prior knowledge question (do this before using the gizmo.)
marla wants a hard - boiled egg for breakfast. the recipe says boil water, then lower the heat so the water is simmering. but marla is in a rush, so she keeps the heat on high as the egg cooks.
do you think the egg will be done faster if the heat is kept on high as the water boils?
explain your answer.
gizmo warm - up
in the phase changes gizmo, select micro view. notice the nitrogen (), oxygen (), and water () molecules.
to start, create ice. set add/remove heat energy to - 200 j/s, click play (), and then click pause () when the container is about half ice, half water. set add/remove heat energy back to 0 j/s, and then click play.

1. observe water molecules in the solid (ice), liquid (water), and gas (air) phases.

a. in which phase(s) do molecules move freely?
b. in which phase(s) are molecules held together?
c. what do you notice about the positions of the ice molecules?
when frozen, water molecules form a hexagon (six - sided shape) pattern.

1. click reset (), and select macro view. set the ice volume to 25 cm³.

a. in which phase(s) is water held in a defined shape?
b. in which phase(s) does the water take the shape of the container?

Explanation:

• Prior Knowledge Question: Once water reaches its boiling point, its temperature remains constant regardless of the heat intensity. So, keeping the heat on high won't cook the egg faster.
• 1A: Molecules move freely in the gas phase as there are weak intermolecular forces.
• 1B: Molecules are held together in the solid and liquid phases due to intermolecular forces like hydrogen - bonding in water.
• 1C: Ice molecules are in a fixed, ordered hexagonal pattern.
• 2A: Water is held in a defined shape in the solid phase (ice) because of its rigid crystal structure.
• 2B: Water takes the shape of the container in the liquid phase as the molecules can flow and move relative to each other.

Answer:

• Prior Knowledge Question: No, the egg will not be done faster. Once water boils, its temperature stays at the boiling - point (100°C at standard pressure) and additional heat just makes it boil faster, not increase the cooking temperature of the egg.
• 1A: Gas
• 1B: Solid and liquid
• 1C: They form a hexagonal pattern.
• 2A: Solid
• 2B: Liquid