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I'd say it all comes down to your physical setup. When studying the Ising model one is usually interested in its behaviour at certain values of temperature and volume. On the other hand, the liquid-gas transition is usually described in a pressure-temperature diagram, i.e., at different but fixed pressures and temperatures. Bottom line: the choice of free ...

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Wood can only be solid because it's a very specific arrangement of atoms. If you liquified or vaporized all the elements in it, they wouldn't be wood. You also can't have liquid crystals, unless you count liquid crystals. Or a liquid computer.

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The Landau model for ferromagnetism has the following expression for the free energy density, as a function of temperature $T$ and magnetization $M$: $$F(T,M)=F_0(T)+\dfrac{a}{2}(T-T_C)M^2+\dfrac{b}{4}M^4+\dfrac{c}{6}M^6+\mathcal{O}(M^6)$$ First order phase transition occurs when the first derivative of $F$ (namely, the entropy) is discontinuous as \$T\to ...

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Normal fluids at fixed pressure are liquid (or solid) at low temperature and gaseous at high temperature. At some temperature the phase transition from liquid to gas occurs. However, at sufficiently high pressure, there is no such phase transition. The critical point is the largest pressure and temperature where the phase transition can be (just barely) ...

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Characteristically, a critical point occurs somewhere anytime you have a continuous phase transistion. That is, if you have two phases of a substance that themselves share their intrinsic symmetries. The classic example is the critical point associated with the liquid gas transition, as you note. Liquids are isotropic and homogenous, gases are isotropic ...

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Most substances can perform a large number of phase transitions. There are even different kinds of phase transitions and sometimes two phases can be connected by more than one process. The quantities governing what phase transition occurs are so-called state variables; temperature and pressure are the best known representatives, but e.g. magnetic fields can ...

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When a substance skips the liquid phase and deposits as a solid directly from its gas phase, it's called deposition. When it evaporates directly from solid to gas it's called sublimation. The key to this happening is the equilibrium vapor pressure of the substance, which is the pressure exerted by its gas phase when it's in thermodynamic equilibrium with ...

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