Critical solution definition

If the temperature is changed the miscibility of the liquids alters, and at a particular temperature the miscibility may become total this is called the critical solution temperature. With rise of temperature the surface of separation between the liquid and vapour phases also vanishes at a definite temperature, and we have the phenomenon of a critical point in the ordinary sense. According to Pawlewski (1883) the critical temperature of the... 

Note 1 An alternative definition of critical solution point refers strictly to liquid-vapor equilibria [3]. 

Stability, systems are intrinsically stable as one homogeneous phase when the temperature is greater than rcnticai- Hence, rcnticai is consistent with the definition of an upper critical solution temperature. Since Sp/SV)t, w, = 0 at rcriacai. small changes in pressure produce enormous changes in density near the critical point. This phenomenon is exploited by physical chemists, who perform lightscattering studies near Tcriticai-... 

In recent years, a number of systems have been examined that also exhibit a lower critical solution temperature (LCST), as shown at the top of Figure 7.1. Here, a more unusual thermodynamic property is exhibited when the polymer phase separates from the solvent after being heated. (One might question the nomenclature the puts die LCST above the UCST, but that is the accepted definition.) LCSTs are more difficult to observe experimentally because they often lie well above the normal boiling points of the solvents. 

Before starting the search for solutions, it is necessary to select among the M decision variables a subset of H variables, Xf, h- 1,..., W, which influence significantly the system performance, and thus will be used by S and included in the definition of the final set of hyperrectangles, X. For this preliminary choice of critical decision variables, other than his or her own specific process knowledge, the decisionmaker can count on a number of auxiliary techniques enumerated in Saraiva and Stephanopoulos (1992c). 

Soil pH is perhaps the most critical and common soil measurement where a definite amount of water is added before a measurement is made. Soil pH is a particularly complicated measurement because the proton can and does exist as a hydronium ion in the soil solution, as an exchangeable ion on the cation exchange sites, and bonded to various soil constituents. Because of these complexities, a soil sample is usually brought to a standard moisture content before a pH measurement is made. By bringing different soils to a common moisture content, they can be compared and analytical results from different laboratories will be comparable. Although there is a number of ways to measure soil pH, typically it is carried out using a pH meter and a pH electrode. 

It has been proposed to define a reduced temperature Tr for a solution of a single electrolyte as the ratio of kgT to the work required to separate a contact +- ion pair, and the reduced density pr as the fraction of the space occupied by the ions. (M+ ) The principal feature on the Tr,pr corresponding states diagram is a coexistence curve for two phases, with an upper critical point as for the liquid-vapor equilibrium of a simple fluid, but with a markedly lower reduced temperature at the critical point than for a simple fluid (with the corresponding definition of the reduced temperature, i.e. the ratio of kjjT to the work required to separate a van der Waals pair.) In the case of a plasma, an ionic fluid without a solvent, the coexistence curve is for the liquid-vapor equilibrium, while for solutions it corresponds to two solution phases of different concentrations in equilibrium. Some non-aqueous solutions are known which do unmix to form two liquid phases of slightly different concentrations. While no examples in aqueous solution are known, the corresponding... 

---