A phase change occurs when a substance transitions between different states of matter (solid, liquid, gas) as a result of energy transfer. During a phase change, the energy supplied to or removed from the substance alters the behavior of its particles but does not affect the temperature. For example, during melting or boiling, energy is absorbed to break intermolecular bonds, allowing particles to move more freely, without increasing kinetic energy or temperature. Similarly, during freezing or condensation, energy is released as particles move closer and bond more strongly.