We often here the term in thermodynamics that a particular phase

[mkbh_10]

We often here the term in thermodynamics that a particular phase change is of 1st order , second order . What does the word order imply

 

[torquil]

It has to do with the order of differentiability of a thermodynamic potential when varying a physical parameter so as to cause the phase transition.

It is described here:
http://en.wikipedia.org/wiki/Phase_transition"