A change in a feature of a physical system that results in a discrete transition of that system to another state. For example, the melting of ice is a phase transition of water from a solid phase to a liquid phase. Phase transitions often involve the absorption or emission of energy from the system; ice, at 0 ° Celsius, must absorb a considerable amount of heat energy to become water. See also state of matter thermodynamics.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.