# Phase equilibrium - beyond critical point

#### KLscilevothma

phase equilibrium -- beyond critical point

In a phase diagram, at critical point, liquid phase is indistinguishable from vapour, and beyond which, only vapour can be found. Matter has four states, liquid, solid, gas and plasma. Can we include plasma state in a phase diagram? If yes, how should the phase diagram be drawn? Also, I'm not very clear of what plasma state is, could someone give me a URL/explanation on that please.

Related Biology and Medical News on Phys.org

#### Ivan Seeking

Staff Emeritus
Gold Member
Re: phase equilibrium -- beyond critical point

Originally posted by KL Kam
In a phase diagram, at critical point, liquid phase is indistinguishable from vapour, and beyond which, only vapour can be found. Matter has four states, liquid, solid, gas and plasma. Can we include plasma state in a phase diagram? If yes, how should the phase diagram be drawn? Also, I'm not very clear of what plasma state is, could someone give me a URL/explanation on that please.
A plasma is just an ionized gas. I don't think phase transistions apply here since this is not a thermodynamic state, ie. we don't arrive at this state through a thermodynamic process...less the fact that we need a gas. Ionization can only be explained through QM.

How's the studying coming along?

#### KLscilevothma

Re: Re: phase equilibrium -- beyond critical point

Originally posted by Ivan Seeking
I don't think phase transistions apply here since this is not a thermodynamic state, ie. we don't arrive at this state through a thermodynamic process...less the fact that we need a gas. Ionization can only be explained through QM.

How's the studying coming along?
An elememtary question, what is a thermodynamic state? I know if we apply lots of energy to matter, say sodium, it will change from solid state to liquid state, then to vapour state, and then turn into plasma, but I don't understand the term "thermodynamic state".

The last exam paper that requires me to study beforehand will be finished in 5 hours.

#### Ivan Seeking

Staff Emeritus
Gold Member
Re: Re: Re: phase equilibrium -- beyond critical point

Originally posted by KL Kam
I know if we apply lots of energy to matter, say sodium, it will change from solid state to liquid state, then to vapour state, and then turn into plasma..
Hmmmm. True. I guess this gets to be risky business since it all come down to QM eventually. I guess what I meant was a state that can be described by the principles of thermodynamics - statistical calculations and such. I think the problem is that Classical Thermodynamics cannot address the formation of plasma. But you are correct that it is just another state dependent on the energy in the system. By this, I think that we could argue that fusion is a phase transition also. So, perhaps you touch on Quantum Thermodynamics with this question? I also think your point is valid. These do seem like other phase transitions. This could also be a simple matter of definition; the ones that we use fail to address your suggestion.

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving