# Why does the plot of volume and temperature have a kink in a second order phase transition? The $$(b)$$ part of the figure shows how thermodynamic variables change in a second order phase transformation. We observe there is a kink in the plot of volume with temperature.

Why is that so?

• Because they are second order phase transitions? GO back to the definition of a second order phase transition, such as in en.wikipedia.org/wiki/Phase_transition. – Jon Custer Dec 10 '20 at 19:34
• Thank you Mr Jon Custer. I was interested in the actual mechanism as to why the kink was there. – Kashmiri Dec 11 '20 at 4:14
• An example for a), first order of phase transition, is the one about liquid water $\ce{->}$ gaseous water / steam; you have both a sudden jump in $\Delta{}V/\Delta{}T$ and the energy needed for this transition ends in latent heat. Guess what, not all transitions involve latent heat (i.e., compare with your lecture notes, references at disposition, etc.). – Buttonwood Dec 11 '20 at 13:57
• Thank you buttonworth. I was interested in the second order transition in which there isn't a jump but just a bend in the plot of V with T – Kashmiri Dec 11 '20 at 14:16
• @YasirSadiq - because instead of a jump in volume, there is a jump in the derivative of volume (for example). And for a third order phase transition there would be a jump in the second derivative of volume... That is how the order of a phase transition is defined. – Jon Custer Dec 11 '20 at 17:01