A phase change or phase transition is a change between solid, liquid, gaseous, and sometimes plasma states of matter. The states of matter differ in the organization of particles and their energy. The main factors that cause phase changes are changes in temperature and pressure. At the phase transition, such as the boiling point between liquid and gas phases, the two states of matter have identical free energies and are equally likely to exist.
Here is a list of the key phase changes between solids, liquids, gases, and plasma. There are six phase changes between solids, liquids, and gases, and eight phase changes if you include plasma. There are additional phase changes if you explore condensed matter physics or metallurgy.
List of Phase Changes
Here is a list of the phase changes of matter.
- Melting (Solid → Liquid)
- Freezing (Liquid → Solid)
- Vaporization or Evaporation (Liquid → Gas)
- Condensation (Gas → Liquid)
- Deposition (Gas → Solid)
- Sublimation (Solid → Gas)
- Ionization (Gas → Plasma)
- Deionization or Recombination (Plasma → Gas)
Phase Changes for States of Matter
Another way to learn phase changes is to associate them with the starting state of matter:
- Solid: A solid can melt into liquid or sublimate into gas.
- Liquid: A liquid can freeze into a solid or vaporize into a gas.
- Gas: A gas can deposit into a solid, condense into a liquid, or ionize into plasma.
- Plasma: Plasma can deionize or recombine to form a gas. Remember, plasma is like a gas, except the particles are even further apart and they are ionized.
Examples of Phase Changes
- Melting: Solid ice melts into liquid water.
- Freezing: Freezing water changes it from a liquid into solid ice.
- Vaporization: An example of vaporization is the evaporation of rubbing alcohol from skin into the air.
- Condensation: A good example of condensation is dew formation from water vapor in air.
- Deposition: Hoarfrost is grayish-white frost that forms during clear, cold weather when water vapor deposits as ice. Another example is deposition of silver vapor onto glass to form a silver mirror.
- Sublimation: Dry ice undergoes sublimation to change from solid carbon dioxide directly into carbon dioxide gas. Another example is the transition from ice directly into water vapor on a cold, windy winter day.
- Ionization: When you turn on a plasma ball toy, the noble gases inside are ionized by an electric charge and become plasma. The aurora is another example of ionization.
- Deionization or Recombination: Lightning is an example of plasma. After a lightning strike, nitrogen ions eventually draw closer together and lose their charge to become N2 gas.
Why Phase Changes Occur
Most phase changes occur because of a change in the energy of the system. Increasing temperature gives atoms and molecules more kinetic energy, helping them break bonds and move further apart. Similarly, decreasing temperature slows down particles and makes it easier for them to gain rigid structure. Increasing pressure forces particle together, while decreasing pressure lets them move away from each other. You can use a phase diagram to predict whether a substance will be a solid, liquid, or gas at a given combination of temperature and pressure. Matter must be ionized to become plasma. So, you can increase temperature to form ions, but decreasing pressure doesn’t automatically make plasma even if you go all the way to a vacuum.
References
- Blundell, Stephen J.; Katherine M. Blundell (2008). Concepts in Thermal Physics. Oxford University Press. ISBN 978-0-19-856770-7.
- IUPAC (1997). “Phase Transition”. Compendium of Chemical Terminology (2nd ed.) (the “Gold Book”). ISBN 0-9678550-9-8. doi:10.1351/goldbook
- Jaeger, Gregg (1 May 1998). “The Ehrenfest Classification of Phase Transitions: Introduction and Evolution”. Archive for History of Exact Sciences. 53 (1): 51–81. doi:10.1007/s004070050021