The above graph is a phase change diagram for water. At points B and D the water is going through a phase change. During the phase changes, what is happening to the temperature and the heat energy?

Question

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The temperature and the heat energy are increasing during a phase change.
The temperature remains constant and the heat energy is increasing during a phase change.
The temperature is increasing and the heat energy remains constant during a phase change.
The temperature and the heat energy remain constant during a phase change.
you have to look at the graph and see what is happening at section B and D. These sections represent phase changes of melting and freezing. What happens to temperature and heat energy at these sections? If you have a horizontal line (----) this means the vertical y axis (temperature) is not going up and only the horizontal x axis (heat energy) is increasing.

Answer 1

During phase changes, such as melting and freezing, the temperature of the substance remains constant while the heat energy is either being absorbed (during melting) or released (during freezing). This is because the energy being added or removed is used to break or form the bonds between molecules rather than to change their kinetic energy (which is what temperature measures).

Therefore, at points B and D on the phase change diagram for water, the correct statement is:

The temperature remains constant and the heat energy is increasing during a phase change.