Lesson 2.4 Changing State - Freezing 2025

1. As the water freezes, does the top surface of the water go up, go down, or stay the same?

• goes up slightly

• goes down slightly

• stays the same

Answer explanation

As water freezes, it expands, causing the volume to increase. This expansion results in the top surface of the water rising slightly, making the correct answer 'goes up slightly'.

2. Assuming that no new water molecules entered the glass while the water was freezing, would you say that frozen water (ice) takes up more space than liquid water, less space, or about the same?

• more space

• less space

• the same amount of space

Answer explanation

Frozen water (ice) takes up more space than liquid water due to its molecular structure. When water freezes, its molecules arrange in a crystalline lattice that is less dense, causing ice to expand and occupy more volume.

3. If you think about the water molecules as liquid water freezes, would you say they get closer together, further apart, or stay at about the same distance from one another?

• closer together

• further apart

• stay at the same distance from one another

Answer explanation

As water freezes, the molecules form a crystalline structure, which causes them to be further apart than in liquid form. This is why ice is less dense than liquid water.

4. In these models of liquid water and ice, you can see that the water molecules in liquid water are very close together, but that the molecules in ice are arranged in a pattern that makes them further apart. This is why ice takes up more room in a container than the liquid water it came from. Sometimes in the winter when water gets into cracks in the road, the water freezes and the road breaks apart and forms a pothole. Explain why you think the freezing of water could cause this to happen.

Answer explanation

When water freezes, it expands and takes up more space. This expansion can exert pressure on the surrounding road material, causing cracks to widen and eventually leading to potholes as the ice pushes against the road.

5. In this experiment, a thin layer of ice forms on the outside of the can. Where do you think the water molecules came from that ended up frozen on the outside of the can?

• they leaked through the can

• they came from water vapor in the air

Answer explanation

The water molecules that froze on the outside of the can came from water vapor in the air. As the can cools, the moisture in the air condenses and freezes, forming a layer of ice.

6. What happened to the speed of the water vapor molecules that came in contact with the cold can?

• they slowed down

• they stayed at the same speed

• they sped up

Answer explanation

When water vapor molecules contact a cold can, they lose energy and slow down. This is because the lower temperature of the can reduces the kinetic energy of the molecules, leading to a decrease in their speed.

7. What happened to the state of the water vapor molecules as they contacted the cold can?

• the state changed from solid to liquid to gas

• the state changed from gas to liquid to solid

• the state changed from liquid to gas

Answer explanation

As the water vapor molecules contacted the cold can, they lost energy and condensed from gas to liquid. If the temperature is low enough, they can further freeze into solid, thus changing from gas to liquid to solid.

8. When water freezes, the water molecules have slowed down enough that their ____________________ arrange them into fixed positions.

• colors

• numbers

• attractions

• molecules

Answer explanation

When water freezes, the water molecules slow down, allowing their attractions to dominate. These attractions cause the molecules to arrange into fixed positions, forming a solid structure, which is ice.

9. Water molecules freeze in a ________________ pattern and the molecules are further apart than they were in liquid water.

• triangular

• pentaganol

• hexagonal

• octagonal

Answer explanation

Water molecules freeze in a hexagonal pattern, which is a result of hydrogen bonding. This arrangement causes the molecules to be further apart than in liquid water, leading to ice being less dense than water.

10. Even though the ice is cold, the molecules still have motion. They ____________ but cannot move past one another.

• slide

• vibrate

• freeze

• rotate

Answer explanation

In ice, molecules are closely packed and cannot move past one another. They vibrate in place due to thermal energy, which allows for motion despite the cold temperature. Thus, 'vibrate' is the correct choice.