|
Results for boiling point
|
On this page:
|
The boiling point of a liquid is the temperature at which the liquid and vapor phases are in equilibrium with each other at a specified pressure. Therefore, the boiling point is the temperature at which the vapor pressure of the liquid is equal to the applied pressure on the liquid. The boiling point at a pressure of 1 atmosphere is called the normal boiling point.
For a pure substance at a particular pressure P, the stable phase is the vapor phase at temperatures immediately above the boiling point and is the liquid phase at temperatures immediately below the boiling point. The liquid-vapor equilibrium line on the phase diagram of a pure substance gives the boiling point as a function of pressure. Alternatively, this line gives the vapor pressure of the liquid as a function of temperature. The vapor pressure of water is 1 atm (101.325 kilopascals) at 100°C (212°F), the normal boiling point of water. The vapor pressure of water is 3.2 kPa (0.031 atm) at 25°C (77°F), so the boiling point of water at 3.2 kPa is 25°C. The liquid-vapor equilibrium line on the phase diagram of a pure substance begins at the triple point (where solid, liquid, and vapor coexist in equilibrium) and ends at the critical point, where the densities of the liquid and vapor phases have become equal. For pressures below the triple-point pressure or above the critical-point pressure, the boiling point is meaningless. Carbon dioxide has a triple-point pressure of 5.11 atm (518 kPa), so carbon dioxide has no normal boiling point. See also Triple point; Vapor pressure.
The normal boiling point is high for liquids with strong intermolecular attractions and low for liquids with weak intermolecular attractions. Helium has the lowest normal boiling point, 4.2 K (−268.9°C). Some other normal boiling points are 111.1 K (−162°C) for CH4, 450°C (842°F) for n-C30H62, 1465°C (2669°F) for NaCl, and 5555°C (10031°F) for tungsten.
The rate of change of the boiling-point absolute temperature Tb of a pure substance with pressure is given by the equation below. ΔHvap,m is the molar enthalpy (heat) of vaporization, and ΔVvap,m is the molar volume change on vaporization. 
The quantity ΔHvap,m/Tb is ΔSvap,m, the molar entropy of vaporization. The molar entropy of vaporization at the normal boiling point (nbp) is given approximately by Trouton's rule: ΔSvap,m,nbp ≈ 87 J/mol K (21 cal/mol K). Trouton's rule fails for highly polar liquids (especially hydrogen-bonded liquids). It also fails for liquids boiling at very low or very high temperatures, because the molar volume of the vapor changes with temperature and the entropy of a gas depends on its volume.
When a pure liquid is boiled at fixed pressure, the temperature remains constant until all the liquid has vaporized. When a solution is boiled at fixed pressure, the composition of the vapor usually differs from that of the liquid, and the change in liquid composition during boiling changes the boiling point. Thus the boiling process occurs over a range of temperatures for a solution. An exception is an azeotrope, which is a solution that boils entirely at a constant temperature because the vapor in equilibrium with the solution has the same composition as the solution. In fractional distillation, the variation of boiling point with composition is used to separate liquid mixtures into their components. See also Azeotropic mixture; Distillation; Phase equilibrium.
A climax or crisis; a high degree of fury, excitement, or outrage. For example, The union's disgust with management has reached the boiling point. This metaphoric term alludes to the temperature at which water boils. [Second half of 1700s]
The temperature at which the vapor pressure within a liquid equals atmospheric pressure.
For more information on boiling point, visit Britannica.com.
The temperature at which a given material changes from a liquid to a gas. The boiling point is the same temperature as the condensation point. (See phases of matter.)
Base pair.
The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.[1][2][3][4] A liquid in a vacuum environment has a lower boiling point than when the liquid is at atmospheric pressure. And a liquid in a high pressure environment has a higher boiling point than when the liquid is at atmospheric pressure. In other words, all liquids have an infinite number of boiling points.
The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the special case at which the vapor pressure of the liquid equals the ambient atmospheric pressure.[5][6] At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and lift the liquid to form bubbles inside the bulk of the liquid.
The heat of vaporization is the amount of heat required to convert or vaporize a saturated liquid (i.e., a liquid at its boiling point) into a vapor.
Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation. Evaporation is a surface phenomenon in which molecules located near the vapor/liquid surface escape into the vapor phase. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, resulting in the formation of vapor bubbles within the liquid.
A saturated liquid contains as much thermal energy as it can without boiling (or conversely a saturated vapor contains as little thermal energy as it can without condensing).
Saturation temperature means boiling point. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase change.
If the pressure in a system remains constant (isobaric), a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy (heat) is removed. Similarly, a liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied.
The boiling point corresponds to the temperature at which the vapor pressure of the liquid equals the surrounding environmental pressure. Thus, the boiling point is dependent on the pressure. Usually, boiling points are published with respect to atmospheric pressure (101.325 kilopascals or 1 atm). At higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased pressure up to the critical point, where the gas and liquid properties become identical. The boiling point cannot be increased beyond the critical point. Likewise, the boiling point decreases with decreasing pressure until the triple point is reached. The boiling point cannot be reduced below the triple point.
If the heat of vaporization and the vapor pressure of a liquid at a certain temperature is known, the normal boiling point can be calculated by using the Clausius-Clapeyron equation thus:
![T_B = \Bigg(\frac{\,R\,[\,\ln(P_0)-\ln(101.325)\,]}{\Delta H_{vap}}+\frac{1}{T_0}\Bigg)^{-1}](http://content.answers.com/main/content/wp/en/math/a/5/7/a571f71f70413a83967ee40e73bf6dd8.png)
| where: | |
| TB | = the normal boiling point, K |
|---|---|
| R | = the ideal gas constant, 8.314 J · K-1 · mol-1 |
| P0 | = is the vapor pressure at a given temperature, kPa |
| 101.325 | = atmospheric pressure, kPa |
| ΔHvap | = the heat of vaporization of the liquid, J/mol |
| T0 | = the given temperature, K |
| ln | = the natural logarithm to the base e |
Saturation Pressure, or vapor point, is the pressure for a corresponding saturation temperature at which a liquid boils into its vapor phase. Saturation pressure and saturation temperature have a direct relationship: as saturation pressure is increased so is saturation temperature.
If the temperature in a system remains constant (an isothermal system), vapor at saturation pressure and temperature will begin to condense into its liquid phase as the system pressure is increased. Similarly, a liquid at saturation pressure and temperature will tend to flash into its vapor phase as system pressure is decreased.
The higher is the vapor pressure of a liquid at a given temperature, the lower is the normal boiling point (i.e., the boiling point at atmospheric pressure) of the liquid.
The vapor pressure chart to the right has graphs of the vapor pressures versus temperatures for a variety of liquids.[7] As can be seen in the chart, the liquids with the highest vapor pressures have the lowest normal boiling points.
For example, at any given temperature, propane has the highest vapor pressure of any of the liquids in the chart. It also has the lowest normal boiling point(-43.7 °C), which is where the vapor pressure curve of propane (the purple line) intersects the horizontal pressure line of one atmosphere (atm) of absolute vapor pressure.
In terms of intermolecular interactions, the boiling point represents the point at which the liquid molecules possess enough thermal energy to overcome the various intermolecular attractions binding the molecules into the liquid (eg. dipole-dipole attraction, instantaneous-dipole induced-dipole attractions, and hydrogen bonds). Therefore the boiling point is also an indicator of the strength of these attractive forces.
The boiling point of water is 100 °C (212
For purists, the normal boiling point of water is 99.97 degrees Celsius at a pressure of 1 atm (i.e., 101.325 kPa). Until 1982 this was also the standard boiling point of water, but the IUPAC now recommends a standard pressure of 1 bar (100 kPa). At this slightly reduced pressure, the standard boiling point of water is 99.61 degrees Celsius.
The element with the lowest boiling point is helium. Both the boiling points of rhenium and tungsten exceed 5000 K at standard pressure. Due to the experimental difficulty of precisely measuring extreme temperatures without bias, there is some discrepancy in the literature as to whether tungsten or rhenium has the higher boiling point.[8]
| Phases of Matter (list) |
|---|
| Solid • Liquid • Gas • Plasma • Colloid • Supercritical fluid • Superfluid • Supersolid • Degenerate matter • Quark-gluon plasma • Fermionic condensate • Bose–Einstein condensate • Strange matter • Melting point • Boiling point • Triple point • Critical point • Equation of state • Cooling curve |
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Join the WikiAnswers Q&A community. Post a question or answer questions about "boiling point" at WikiAnswers.
Copyrights:
 |
 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
 |
| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
 |
| Idioms. The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Company. All rights reserved. Read more |
 |
| Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved. Read more |
 |
| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
 |
| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/ Read more |
|
| Science Dictionary. The New Dictionary of Cultural Literacy, Third Edition Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin. All rights reserved. Read more |
|
| Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
 |
| Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Boiling point". Read more |
Search for answers directly from your browser with the FREE Answers.com Toolbar!
Click here to download now. 
Get Answers your way! Check out all our free tools and products.
Mentioned In:
