What causes a Phase-Transition? 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 synchronizes in some specific vector, facilitating the phase transition? Finally could it be that the liquid thermodynamically self organizes 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 phenomenon to me would be great.
 A: 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.
A: 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.
A: Phase Transitions are the sudden changes in the properties of the thermodynamic system such as volume, or magnetization as temperature varied. It is caused by variation in thermodynamic parameter. according to Baumgärtner, A., Binder, K., Hansen, J.P.,  Kalos, M., Kehr, K., Landau,  D., Saito, Y.  (2013).  Applications of the Monte Carlo method in statistical physics Vol. 36: Springer Science &              Business Media.
