A phase change is a change in the state of matter of a substance. The energy of a phase change is the difference in the enthalpy of the substance in the two states. The enthalpy of a substance is the sum of the internal energy and the product of the pressure and volume of the substance. The internal energy of a substance is the energy of the molecules of the substance. The pressure of a substance is the force per unit area exerted by the molecules of the substance on the walls of the container. The volume of a substance is the space occupied by the molecules of the substance.

Other related questions:

Q: What is true about phase change?

A: There are three main types of phase changes- melting, freezing, and vaporization (or boiling).

In a solid, the molecules are closely packed together and held in place by strong intermolecular forces. In a liquid, the molecules are still close together but are able to move around each other. In a gas, the molecules are far apart and move freely.

A phase change occurs when the energy of the molecules changes enough to overcome the intermolecular forces holding them in place. For example, when a solid is heated, the molecules gain energy and begin to vibrate. As the temperature increases, the vibrations become more and more violent until the molecules have enough energy to overcome the forces holding them in place and they are able to move freely. This is the melting point.

Q: What is energy in phase changes?

A: In a phase change, energy is required to change the phase of a substance. For example, when water changes from a liquid to a gas, energy is required to break the bonds between the water molecules. This energy is called latent heat.

Q: How does the energy of a system change during a phase change?

A: The energy of a system during a phase change is dependent on the specific process occurring. For example, during melting, the system gains heat from the surroundings until the melting point is reached. Once the melting point is reached, the system will remain at that temperature until all of the solid has turned to liquid.


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