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In terms of chemical potential, at the boiling point, the liquid and gas phases have the same chemical potential. Adding a nonvolatile solute lowers the solvent’s chemical potential in the liquid phase, but the gas phase remains unaffected. This shifts the equilibrium between phases to a higher temperature, elevating the boiling point.
This technique is used when the boiling point of the desired compound is difficult to achieve or will cause the compound to decompose. [1] Reduced pressures decrease the boiling point of compounds. The reduction in boiling point can be calculated using a temperature-pressure nomograph using the Clausius–Clapeyron relation. [2]
A liquid in a partial vacuum, i.e., under a lower pressure, has a lower boiling point than when that liquid is at atmospheric pressure. Because of this, water boils at 100°C (or with scientific precision: 99.97 °C (211.95 °F)) under standard pressure at sea level, but at 93.4 °C (200.1 °F) at 1,905 metres (6,250 ft) [ 3 ] altitude.
This Wikipedia page provides a comprehensive list of boiling and freezing points for various solvents.
The higher the vapor pressure of a liquid at a given temperature, the lower the normal boiling point of the liquid. The vapor pressure chart displayed has graphs of the vapor pressures versus temperatures for a variety of liquids. [9] As can be seen in the chart, the liquids with the highest vapor pressures have the lowest normal boiling points.
In chemical engineering, azeotropic distillation usually refers to the specific technique of adding another component to generate a new, lower-boiling azeotrope that is heterogeneous (e.g. producing two, immiscible liquid phases), such as the example below with the addition of benzene to water and ethanol.
A plot of typical polymer solution phase behavior including two critical points: a LCST and an UCST. The liquid–liquid critical point of a solution, which occurs at the critical solution temperature, occurs at the limit of the two-phase region of the phase diagram. In other words, it is the point at which an infinitesimal change in some ...
This reduces the boiling point of the liquid to be evaporated, thereby reducing or eliminating the need for heat in both the boiling and condensation processes. There are other advantages, such as the ability to distill liquids with high boiling points and avoiding decomposition of substances that are heat sensitive. [2]