# Microscopic difference between gas and liquid

• jostpuur
In summary, the conversation discusses the Ising model and its phase transition behavior, as well as the possibility of similar theoretical models for concrete examples such as the difference between gas and liquid and the use of renormalization techniques to understand condensation and vaporization. It is mentioned that there is no clear microscopic difference between gas and liquid, and that the renormalization group is applicable to universal behavior near the critical point.
jostpuur
I am familiar with Ising model, and the phase transition behavior the interacting "arrows" attached to lattice points exhibit. Now, I'm curious to know if similar theoretical models exist of more concrete examples. For example, what is the microscopic difference between gas and liquid? Can the condensation and vaporization be understood through the use of some renormalization techniques?

jostpuur said:
For example, what is the microscopic difference between gas and liquid? Can the condensation and vaporization be understood through the use of some renormalization techniques?
Unfortunately no, as you can move continuously from liquid to gas (by going around the triple point on the phase diagram). Since there is no transition along this path, it suggests there is no way to distinguish them microscopically... they are just both fluids.

You probably meant the critical point, and not the triple point?

I see that it is possible to go from gas to liquid smoothly, but on the other hand, it is also possible to go from gas to liquid abruptly, so there must be some clear microscopical difference. This is a kind of thing, where it is frustrating that many sources merely mentions various things, leaving it ambiguous what is really known and what is not known. If it is the case that there is no microscopic theoretical model about the phase change between gas and liquid, it is of course very exciting, because one should consider it as a challenge But I would prefer being more certain about it...

The best analogy I've hear is it's like a wall between 2 rooms, but the wall has a gap at the top. Is it 2 rooms or one room?

The renormalization group is applicable to universal behavior near the critical point.

## 1. What is the main difference between gas and liquid at a microscopic level?

At a microscopic level, the main difference between gas and liquid is the arrangement of their particles. Gas particles are spread out and move freely, while liquid particles are closer together and have more restricted movement.

## 2. How do gas and liquid particles interact with each other?

Gas particles have very weak interactions with each other and can easily move past one another. Liquid particles, on the other hand, have stronger intermolecular forces that cause them to stick together and move as a cohesive unit.

## 3. What causes gas and liquid particles to have different densities?

The density of a substance is determined by the mass of its particles and the amount of space they occupy. Gas particles have low mass and are spread out, resulting in a lower density. Liquid particles have higher mass and are more closely packed, leading to a higher density.

## 4. How do the properties of gas and liquid change at different temperatures?

As temperature increases, gas particles gain more kinetic energy and move faster, spreading out and increasing in volume. Liquid particles also gain kinetic energy, but their intermolecular forces prevent them from spreading out as much, causing them to expand slightly and become less dense.

## 5. Can gas and liquid particles change state?

Yes, gas and liquid particles can change state through the process of phase transition. Gas particles can condense into liquid form through cooling or increasing pressure, while liquid particles can evaporate into gas form when heated or when the surface area is increased.

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