Liquid-Vapor Critical Point
– The liquid-vapor critical point is the high-temperature extreme of the liquid-gas phase boundary.
– The critical point of water occurs at 647.096K and 22.064 megapascals.
– Near the critical point, the physical properties of the liquid and vapor change dramatically.
– At the critical point, only one phase exists and the heat of vaporization is zero.
– Above the critical point, there exists a state of matter called a supercritical fluid.
History and Theory of the Critical Point
– The existence of a critical point was first discovered by Charles Cagniard de la Tour in 1822.
– Dmitri Mendeleev named the critical point in 1860, and Thomas Andrews further studied it in 1869.
– Cagniard showed that carbon dioxide could be liquefied at a certain temperature and pressure.
– Mendeleev and Andrews contributed to the understanding of critical points in various substances.
– The critical point has been a subject of scientific interest for centuries.
– The van der Waals equation can be used to compute the critical point, but it is not accurate near the critical point.
– Reduced state variables are defined to analyze properties of fluids near the critical point.
– The principle of corresponding states suggests that substances at equal reduced pressures and temperatures have equal reduced volumes.
– For some gases, there is an additional correction factor called Newton’s correction.
– The critical temperature and pressure can vary depending on the substance and pressure range.
Table of Liquid-Vapor Critical Temperature and Pressure
– Argon has a critical temperature of -122.4°C and a critical pressure of 48.1atm.
– Ammonia has a critical temperature of 132.4°C and a critical pressure of 111.3atm.
– R-134a has a critical temperature of 101.06°C and a critical pressure of 40.06atm.
– R-410A has a critical temperature of 72.8°C and a critical pressure of 47.08atm.
– Water has a critical temperature of 373.946°C and a critical pressure of 217.7atm.
Mixtures: Liquid-Liquid Critical Point
– The liquid-liquid critical point of a solution occurs at the critical solution temperature.
– It represents the temperature-concentration extremum of the spinodal curve.
– There are two types of liquid-liquid critical points: the upper critical solution temperature (UCST) and the lower critical solution temperature (LCST).
– The UCST is the hottest point at which cooling induces phase separation.
– The LCST is the coldest point at which heating induces phase separation.
Subtopic 1: Definition and Characteristics of the Critical Point
– The critical point is the temperature and pressure at which a substance undergoes a phase transition from a liquid to a gas.
– At the critical point, the liquid and gas phases become indistinguishable, and the substance exhibits unique properties.
– The critical temperature is the highest temperature at which a substance can exist as a liquid.
– The critical pressure is the pressure required to bring about the phase transition at the critical temperature.
– Above the critical point, the substance exists as a supercritical fluid with properties intermediate between a liquid and a gas. Source: https://en.wikipedia.org/wiki/Critical_point_(thermodynamics)
In thermodynamics, a critical point (or critical state) is the end point of a phase equilibrium curve. One example is the liquid–vapor critical point, the end point of the pressure–temperature curve that designates conditions under which a liquid and its vapor can coexist. At higher temperatures, the gas cannot be liquefied by pressure alone. At the critical point, defined by a critical temperature Tc and a critical pressure pc, phase boundaries vanish. Other examples include the liquid–liquid critical points in mixtures, and the ferromagnet–paramagnet transition (Curie temperature) in the absence of an external magnetic field.
