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## Critical point (thermodynamics) In physical chemistry, thermodynamics, chemistry and condensed matter physics, a
In the phase diagram shown, the phase boundary between liquid and gas does not continue indefinitely. Instead, it terminates at a point on the phase diagram called the critical point. This reflects the fact that, at extremely high temperatures and pressures, the liquid and gaseous phases become indistinguishable. In water, the critical point occurs at around 647 °K (374 °C or 705 °F) and 22.064 MPa (3200 PSIA or 218atm). Critical variables are useful for rewriting a varied equation of state into one that applies to all materials. The effect is similar to a normalizing constant. According to renormalization group theory, the defining property of criticality is that the natural length scale characteristic of the structure of the physical system, the so-called correlation length ξ, becomes infinite. There are also lines in phase space along which this happens: these are In equilibrium systems the critical point is reached only by tuning a control parameter precisely. However, in some non-equilibrium systems the critical point is an attractor of the dynamics in a manner that is robust with respect to system parameters, a phenomenon referred to as self-organized criticality. The critical point is described by a conformal field theory. ## See also- Critical temperature
- Phase transition
- Scale invariance
- Conformal field theory
- Critical exponents
- Percolation thresholds
- Self-organized criticality
- Triple point
- Supercritical fluid, Supercritical drying, Supercritical water oxidation
- Rushbrooke inequality
- Widom scaling
Categories: Phase changes | Statistical mechanics | Condensed matter physics |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Critical_point_(thermodynamics)". A list of authors is available in Wikipedia. |