Back to School Sale
Back to School Sale


Why does the temperature remain constant as a pure substance undergoes a phase change, such as liquid to gas?
Asked by: Amber


Temperature is a macroscopic quantity of matter which is related to the degrees of freedom of particles. In the case of a monatomic gas this is simply the translational motion (kinetic energy) of the particles. When a substance goes through a phase change, inter particle forces have to be broken (or formed). Therefore, when heating a liquid say, many of the inter particle forces have to be broken to vaporise the liquid, which takes energy. So when a liquid is heated and it reaches the vaporisation point all the heat going into the liquid is used to break these bonds instead of increasing the energy in the degrees of freedom (eg kinetic energy). This is called latent heat. Once the liquid has been fully vaporised energy any further heat applied will go into increasing the energy in the degrees of freedom, thus increasing the temperature.
Answered by: Martin Archer, Physics Student, Imperial College London, UK
xUmp Science eStore

Science Quote

J. Robert Oppenheimer Photo

'There must be no barriers for freedom of inquiry. There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors.'

J. Robert Oppenheimer

- All rights reserved. © Copyright '1995-'2018