Changes in Energy on the Molecular Level

Boiling is the process where a liquid changes to a gas throughout the substance at a specific temperature.

Heat is defined as the transfer of thermal energy between objects due to a temperature difference.

Temperature is a measure of the average kinetic energy of the particles in a substance. As particles move faster, their kinetic energy increases, which corresponds to a higher temperature.

Adding thermal energy increases kinetic energy and particle vibration, causing transitions like solid to liquid or liquid to gas. Option A describes removing energy, which causes cooling and condensation or freezing.

In solids, particles are held in a fixed, orderly structure and vibrate about fixed positions. While they are closely packed, the defining characteristic of their motion is vibration.

Gas particles are characterized by high kinetic energy, random motion, and large distances between them. They are not tightly packed, as they expand to fill their container.

Liquids have a definite volume and are relatively incompressible, but they do not expand to fill any available space like gases do. That behavior is specific to gases.

Melting is the phase transition where a solid gains enough thermal energy to overcome the forces holding it in a rigid structure, turning it into a liquid.

Condensation occurs when gas particles lose kinetic energy and slow down enough for intermolecular forces to pull them together into a liquid state.

Kinetic energy is defined as the energy an object possesses due to its motion. Potential energy is stored energy, and heat is energy transfer.

A liquid has a fixed volume because the particles are close together, but it lacks a fixed shape because the particles can slide past one another.

Heat is defined as the transfer of thermal energy between systems due to a temperature difference.

Freezing is the phase change where a liquid loses enough thermal energy to become a solid.