Question

When a solid is in the process of changing into a liquid and extra energy is added to the system, the temperature does not change.

What happens to this extra energy?
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A. The bonds between molecules are unaffected because the average kinetic energy does not change. Therefore, the molecular motion must increase.

B. The molecular motion of the water must increase while energy in the bonds decreases in order to keep the average kinetic energy the same.

C. The molecular motion does not change because the average kinetic energy does not change. The bonds are unaffected, because bonds do not change when going from solids to liquids. The energy must be needed somewhere else.

D. The temperature does not change during a phase change because the average kinetic energy does not change. Therefore, the potential energy in the bonds between molecules must change.

Answer 1

D. The temperature does not change during a phase change because the average kinetic energy does not change. Therefore, the potential energy in the bonds between molecules must change.

Step-by-step explanation:

Fusion is the change from a solid to a liquid state. It occurs when a body, subjected to a given pressure, receives heat and its temperature reaches a certain value, at that moment the temperature does not change, during the phase change because the average kinetic energy does not change. Therefore, the potential energy in the bonds between molecules must change.

The amount of heat that the body must receive in order to become totally liquid, depends on the substance that constitutes it.

In general, when a substance is in the solid state, it has a well-defined shape. Its atoms are organized neatly in a structure called a crystalline network.

When it receives heat, the atoms that form the solid increase its vibration, increasing its temperature.

If the energy received increases, the vibration of the atoms will undo the crystalline network and the body will go into a liquid state.

Answer 2

D. The temperature does not change during a phase change because the average kinetic energy does not change. Therefore, the potential energy in the bonds between molecules must change.

Step-by-step explanation:

When there is a change of state (for example, from solid into a liquid, as in this example), when energy is added to the system, the temperature of the substance does not change.

The reason for this is that the energy supplied is no longer used to increase the average kinetic energy of the particle, but instead it is used to break the bonds between the different particles/molecules. For instance, since in this case the substance is changing from solid to liquid, all the energy supplied during the phase change is used to break the bonds between the molecules of the solid: when the process is done, all the molecules will be free to slide past each other, and the substance has turned completely into a liquid.

The bonds between molecules store potential energy: therefore, this means that the energy supplied during the phase change is not used to change the kinetic energy, but to change the potential energy in the bonds between the molecules.