Boiling point Definition and 128 Threads

The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water boils at 100 °C (212 °F) at sea level, but at 93.4 °C (200.1 °F) at 1,905 metres (6,250 ft) altitude. For a given pressure, different liquids will boil at different temperatures.
The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the special case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level, one atmosphere. At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid. The standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of one bar.The heat of vaporization is the energy required to transform a given quantity (a mol, kg, pound, etc.) of a substance from a liquid into a gas at a given pressure (often atmospheric pressure).
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 liquid's edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor. 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.

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  1. C

    Help interpreting molal boiling point constant.

    Hi, I'm trying to understand how to explain what the molal boiling point constant is, from interpreting the units (using an example) K_b =3,62K*kg*mol^-1 I would say "One mole of particles are heated up by 3,62kelvin per kg?" but something feels wrong abou saying it that way. Can someone...
  2. teroenza

    Calculate new boiling point with change post-pressure change

    Homework Statement Liquid X boils at 127C, at a pressure of 10.6*10^5 Pa. Its enthalpy of vaporization is 5000 J/mol. At what temperature will it boil if the pressure is raised to 1.08*10^5 Pa? Homework Equations \frac{dT}{dP}=\frac{l}{T(v_{B}-v_{A})}The Attempt at a Solution It seems so...
  3. J

    Why does 2-propanethiol have a lower boiling point than 1-propanethiol

    Homework Statement Consider 2-propanethiol, shown below. Would you expect its boiling point to be higher or lower than that of 1-propanethiol? Why?Homework Equations 1-propanethiol: 2-propanethiol: The Attempt at a Solution I looked it up, and 2-propanethiol does have a lower boiling point...
  4. C

    Archived Finding a lot of answers to water boiling point.

    Homework Statement I had an issue with a professor a while ago. A question was asked, "Why does water boil at 100°C?". What I believe was the targeted answer was something around "Hydrogen bonds." Hydrogen bonds are a valid answer, I believe also correct enough. For clarity purposes, I...
  5. 1

    Vapor pressure given boiling point and heat of vaporization?

    Homework Statement What is the vapor pressure of benzene at 50.0 C? Benzene's boiling point is 80.1 C and its heat of vaporization is 31 kJ/mol Homework Equations The Attempt at a Solution I don't want to be that guy who just says "I don't know" but.. All I know is that: ln P...
  6. S

    Fluid's boiling point dependence as function of pressure

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  7. F

    Calculate freezing point depression and boiling point elevation

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  8. D

    Boiling point of Cyclohexene and 2-methylbut-1-ene

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  9. A

    What factors affect the boiling point of polar molecules?

    arrange the boiling point of the following compounds methoxymethane,butane,pentane and water I quickly arrange like this butane<pentane<methoxymethane<water but after checking wiki,it should be methoxymethane<butane<pentane<water In my knowledge,methoxymethane is a polar molecule,so i...
  10. A

    Pasteurization temperature adjustment for boiling point variations

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  11. R

    Effect of air pressure on boiling point of water

    I know that the boiling point of water is lower when the atmospheric pressure is less (such as at the top of a mountain), but why is that? Once a water molecule has the energy to escape from the binding forces that keep it with the other water moelcules in the liquid, I don't understand why...
  12. Y

    Atmospheric Pressure & Boiling Point of Water: 20 C

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  13. M

    Thermodynamics: dropping iron into thermos of nitrogen at boiling point

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  14. Q

    Methanal vs Hexanone Boiling Point Comparison

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  15. S

    Cracking of hydrocarbons and boiling point of salt water

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  16. T

    Understanding the Boiling Point: Thermodynamic Proof

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  17. D

    Phase Change and Lowest Boiling Point

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  18. M

    Enthelpy of vapourisation vs boiling point

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  19. M

    Determing Boiling Point elevations in lab

    I am trying to get the calculations and the data to match up in lab. The boiling point elevation predicted by the equation does not match up to the one I am getting by direct measurement. What am I doing wrong?
  20. T

    Vapor pressure and the boiling point of a liquid

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  21. P

    Calculating Molal Boiling point elevation constant HELP

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  22. P

    Find True Boiling Point with Barometric Pressure

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  23. Y

    Impurities on melting point and boiling point of water

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  24. S

    Boiling point and vapor pressure

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  25. S

    Boiling point and vapor pressure

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  26. jaumzaum

    Why acetaldehyde has a higher boiling point than ethylamine?

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  27. T

    Calculate Normal Boiling Point of Ethyl Alcohol

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  28. R

    Is the boiling point directly related to the volatility of a substance?

    I know that volatility is more or less proportionally related to vapor pressure. If they are directly related, are they any exceptions where a more volatile substance may have a higher boiling point than a less volatile substance?
  29. T

    Which substance has the highest boiling point?

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  30. H

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  31. A

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  32. P

    Can a vacuum of 1.5 Bar be used to lower the boiling point of liquid?

    Now this may seem a stupid question, but as my old dad said there are no stupid questions only stupid answers! I am distilling some liquid which has a boiling point of about 190 C, I have put the liquid under vacuum of -1bar and the liquid now boils at about 160C, I would like the liquid to...
  33. Z

    Boiling Point before Melting Point?

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  34. T

    Among the six measurements of the boiling point of a silsicon compound

    Question: Among the six measurements of the boiling point of a silsicon compound, the size of the error was 0.07, 0.03,0.14,0.08 and 0.03 degree C . Assuming that these data can be looked upon as a random sample from the population given by. f(x; \theta) = 2 (\theta - x) / \theta2 for 0 < x...
  35. T

    Among six measurement of the boiling point of a silicon compound,

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  36. K

    Boiling point at a certain pressure

    How can one calculate the boiling of a liquid at a pressure different from standard temperature? Am trying to do it using the ideal gas equation, (PV)/T=(P'V')/T' Where P is the STP, V is 22.4l, T= boiling point at STP, P'= new pressure, V' is the new volume and T' is to be found. But is...
  37. S

    What is the Boiling Point of Mineral Oil in a Vacuum?

    Boiling point in a vacuum... Gidday, I am as new here as it gets, and I have a question to post. I have been having a (heated) discussion with regards to the temperature that water boils in a vacumm. Given: @ 10in Hg water will boil at 192F. If you had a pressure reading of 29.7in of...
  38. S

    Boiling Point of Nitrogen References

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  39. A

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  40. A

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  41. C

    Question on the Boiling point of NaCl solution.

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  42. A

    Vapor pressure, its decrease and subsequent lowering of boiling point

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  43. S

    Understanding Boiling Point: Factors That Affect Liquid Vapor Pressure

    Hello! I often read that the boiling point of a liquid is when its vapor pressure is equal to the atmospheric pressure. What I don't understand is why they never take the pressure of the water into consideration? Doesn't water pressure increase as depth increases and wouldn't this have to be...
  44. B

    Can Small Amounts of Chemicals Lower Water's Boiling Point?

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  45. C

    Gas that turn into liquid have a boiling point?

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  46. P

    Boiling Point & Van der Waals Force: Weight Dependency

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  47. W

    Finding normal boiling point given pressure and enthelpy.

    Homework Statement Given the following data, determine the heat of vaporization and normal boiling point of ammonia Temp (K): 200 210 220 230 235 Pressure (respectively)(torr): 65.3 134.3 255.7 456.0 597.0 Homework Equations ln(p2/p1)=-deltaH/R(1/t2-1/t1) The Attempt...
  48. S

    How does molecular shape affect boiling point in organic compounds?

    In organic chemistry, What causes a compound to be more soluble than others? What causes a compound to have a higher boiling point than others? I think the more molecular mass a compound has, the higher boiling point. However, methoxymethane and ethanol both have the same molecular mass...
  49. S

    Question on normal boiling point and enthelpy of vaporization

    Hello all I performed a lab where we put a graduated cylinder filled to 90% with water upside down in a large beaker filled with water and measured the volume of the air bubble inside the graduated cylinder at different temperatures. When I graphed Ln(PH20) vs. 1/T I got a slope of -10412...
  50. D

    Calculating Boiling Point of HF: ΔH and ΔS Equation Analysis

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