Study the phase change diagram for water.

Question

A phase change diagram with five sections. The x-axis is thermal energy, and the y-axis is temperature in degrees Celsius. The line in section A goes up and to the right. Section B is a horizontal line at zero degrees, connecting sections A and C. Section C goes from zero to 100 degrees as a diagonal line moving upward and to the right. Section D is a horizontal line at 100 degrees, connecting sections C and E. The line of section E goes up and to the right from 100 to 200 degrees.
A temperature-energy diagram with five sections.
Long Description

At what interval(s) in the diagram does the thermal energy of the water molecules increase?

Responses

E only
E only

All intervals show an increase in energy.
All intervals show an increase in energy.

A, C, and E
A, C, and E

B and D
B and D

Answer 1

In the phase change diagram you described, the thermal energy of the water molecules increases during the intervals where the temperature is rising. Let's analyze each section based on your descriptions:

• Section A: This section represents the heating of ice (solid) as it increases in temperature from below 0°C to 0°C. The water molecules are gaining energy, so thermal energy increases.

• Section B: This section is horizontal at 0°C, which represents the phase change from solid (ice) to liquid (water). During this phase change, the temperature remains constant while heat energy is absorbed to break molecular bonds, so the thermal energy of the water is not increasing in terms of temperature, even though the energy is still being transferred to facilitate the phase change.

• Section C: This section represents the heating of liquid water as it increases in temperature from 0°C to 100°C. The water molecules are gaining energy, so thermal energy increases here as well.

• Section D: This section is horizontal at 100°C, which represents the phase change from liquid (water) to gas (steam). Similar to section B, the temperature remains constant during this phase change while heat energy is absorbed to convert liquid to gas. So, thermal energy in terms of temperature does not increase here.

• Section E: This section represents the heating of steam (gas) as it increases from 100°C to 200°C. The water molecules are gaining energy in this phase as well, so thermal energy increases.

In summary, the intervals where the thermal energy of the water molecules increases are:

• Section A: Heating ice
• Section C: Heating liquid water
• Section E: Heating steam

Thus, the correct answer from your options would be: A, C, and E.