What causes a Phase-Transition

Question

A phase transition occurs when for example, heat is applied continuously to a liquid and after a certain time it converts into a gas.

How does this process work in detail? Is their a chain reaction that causes to liquid to reach a 'critical' point? Does the liquid syncronises in some specific vector, facilitating the phase transition? Finally could it be that the liquid theromodynamically self organisises into a state that causes the transition?

To paraphrase, what exactly is a 'phase-transition' what occurs before, during and after one?

Any additional comments you think would help explain this phenomenom to me would be great.

This post imported from StackExchange Physics at 2014-04-11 15:48 (UCT), posted by SE-user marscom

Comments

A comment on terminology: a "phase-transition" is usually devoid of dynamical content. It refers to specific macroscopic equilibrium states which separate phases in thermodynamics. The question of what actually happens as one tunes the parameters through the transition is both a different and much more complex problem, depending on parameters beyond just thermodynamic ones. A good introduction to the kinds of problems one sees can be found in the theory of binary alloys. It is a well studied problem as it is crucial to metallurgy, where mechanical properties directly relate to microstructure.

This post imported from StackExchange Physics at 2014-04-11 15:48 (UCT), posted by SE-user genneth

Answer 1

In a very general picture a phase transition is a change of between different states of matter.

The cause for a phase transition is a change of a thermodynamical parameter, such as temperature, pressure, volume or magnetic field. The primary example is a change of temperature as the cause for a phase transition.

What exactly happens on a microscopic level depends on the details of the system, so there is no general statement possible.

The change between different states is so special because several things might happen:

• Change of symmetry (e.g. from continous to discrete)
• Latent heat
• Divergence of specific heat, susceptibility, ...

A good starting point if you are interested in all these phenomena is the Wikipedia article about phase transitions. The underlying theory is in development for several decades, where the works of Landau and Lifshitz provide a good coverage (Statistical Physics Part 1) or any modern introduction to Statistical Physics.

This post imported from StackExchange Physics at 2014-04-11 15:48 (UCT), posted by SE-user Alexander

Answer 2

For an intentionally informal and easy-to-read answer about what happens during the major phase changes, here is an older answer I gave that might be helpful. When reading it, please be assured that I tried to keep the analogy as real -- as physically accurate -- as I possibly could, even while using everyday analogies.

This post imported from StackExchange Physics at 2014-04-11 15:48 (UCT), posted by SE-user Terry Bollinger