The changes in temperature and molecular movement can be described for each of the following phase transitions: boiling, melting, freezing, and sublimation.
Boiling
- Temperature Change: The temperature of the liquid remains constant at the boiling point while it is boiling, despite the addition of heat.
- Molecular Movement: As the liquid reaches its boiling point, molecules gain enough energy to overcome intermolecular forces. They move from a liquid state, where they are relatively close together, to a gas state. The movement becomes much more rapid and less constrained, with gas molecules moving freely and rapidly in all directions.
Melting
- Temperature Change: The temperature of the solid increases until it reaches the melting point, at which it remains constant during the melting process.
- Molecular Movement: In the solid phase, molecular movement is minimal, and molecules vibrate in fixed positions. As heat is applied and the solid reaches its melting point, the molecules begin to gain energy, increasing their vibrational movement. Eventually, they have enough energy to break free from their fixed positions, causing the solid to transition to a liquid state, where they can slide past each other more freely.
Freezing
- Temperature Change: The temperature of the liquid decreases until it reaches the freezing point, at which it remains constant during the freezing process.
- Molecular Movement: As the liquid cools down, molecular movement decreases. When the temperature reaches the freezing point, molecules lose energy and begin to move closer together, forming a solid structure with a more ordered arrangement as they vibrate in fixed positions. The formation of intermolecular bonds leads to the solidification of the liquid.
Sublimation
- Temperature Change: Sublimation can occur at various temperatures, but it typically happens below the melting point of the substance. However, the temperature can remain relatively constant during the process, depending on the surrounding conditions (such as pressure).
- Molecular Movement: In sublimation, solid molecules gain enough energy to bypass the liquid phase and directly enter the gas phase. In the solid state, molecules are tightly packed in a structured arrangement. As they gain energy, they increase their movement and start breaking free from the solid structure, transitioning directly into a gaseous state, where they move freely and occupy more space.
These phase transitions illustrate how energy changes result in changes in temperature and molecular movement, impacting the states of matter.