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The commonly known phases solid, liquid and vapor are separated by phase boundaries, i.e. pressure–temperature combinations where two phases can coexist. At the triple point, all three phases can coexist. However, the liquid–vapor boundary terminates in an endpoint at some critical temperature T c and critical pressure p c. This is the ...
The pressure on a pressure-temperature diagram (such as the water phase diagram shown above) is the partial pressure of the substance in question. A phase diagram in physical chemistry , engineering , mineralogy , and materials science is a type of chart used to show conditions (pressure, temperature, etc.) at which thermodynamically distinct ...
Pressure–temperature phase diagram. The supercritical state is at pressures and temperatures above those of the critical point, but below the pressures required for transformation into a solid. The dashed green line shows the anomalous slope of the solid-liquid phase boundary exhibited by some substances, including water.
Water phase diagram. Y-axis=Pressure in pascals (10 n). X-axis=Temperature in kelvins. S=Solid; L=Liquid; V=Vapour, CP=Critical Point, TP=Triple Point: Date: September 2006: Source: Own work: Author: Eurico Zimbres: Permission (Reusing this file) Free for all use: Other versions: phase diagram with description but without units of measurement
In water, the critical point occurs at around 647 K (374 °C or 705 °F) and 22.064 MPa. An unusual feature of the water phase diagram is that the solid–liquid phase line (illustrated by the dotted green line) has a negative slope. For most substances, the slope is positive as exemplified by the dark green line.
Anisimov et al. (2004), [11] without referring to Frenkel, Fisher, or Widom, reviewed thermodynamic derivatives (specific heat, expansion coefficient, compressibility) and transport coefficients (viscosity, speed of sound) in supercritical water, and found pronounced extrema as a function of pressure up to 100 K above the critical temperature.
In thermodynamics, a critical line is the higher-dimensional equivalent of a critical point. [1] It is the locus of contiguous critical points in a phase diagram.These lines cannot occur for a single substance due to the phase rule, but they can be observed in systems with more variables, such as mixtures.
Reduced properties are also used to define the Peng–Robinson equation of state, a model designed to provide reasonable accuracy near the critical point. [2] They are also used to critical exponents, which describe the behaviour of physical quantities near continuous phase transitions. [3]