What is Vapor: Definition and 272 Discussions

In physics, a vapor (American English) or vapour (British English and Canadian English; see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapor can be condensed to a liquid by increasing the pressure on it without reducing the temperature. A vapor is different from an aerosol. An aerosol is a suspension of tiny particles of liquid, solid, or both within a gas.For example, water has a critical temperature of 647 K (374 °C; 705 °F), which is the highest temperature at which liquid water can exist. In the atmosphere at ordinary temperatures, therefore, gaseous water (known as water vapor) will condense into a liquid if its partial pressure is increased sufficiently.
A vapor may co-exist with a liquid (or a solid). When this is true, the two phases will be in equilibrium, and the gas-partial pressure will be equal to the equilibrium vapor pressure of the liquid (or solid).

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  1. C

    Vapor from high-energy particle collisions?

    Hello, With laser cooling experiments it is possible to create Bose–Einstein condensate. Is there also vapor produced during high-energy particle collisions? And if so, what kind of gasses are it? michel
  2. L

    Diffusion of water vapor in air

    I would like to calculate a diffusion of water vapor in stagnant air. Does anybody know if it is a case of equimolar or nonequimolar diffusion. How one could calculate a diffusion in my case? Which variables is diffusion coefficient dependant on?
  3. N

    Why Liquid Boils: Explaining Saturated Vapor Pressure

    It's hard for me to find the why,bcz most books only give this without any explanation Is there anyone who knows the exact reason?
  4. B

    Vapor Quality calculation

    Water is being used as a coolant by flowing through a channel. I know the mass flow rate of water. And i know the inlet properties of water. I also know that the water is coming out of the channel at a vapor quality of 1. How do i calculate the heat flux that the water is subjected to during...
  5. N

    Density of Saturated Vapor R-134a

    Hi all, Just for fun I am writing a program in Octave for calculating the thermodynamic properties of R-134a. I am using the equations in the Dupont properties booklet. http://www2.dupont.com/Refrigerants/en_US/products/Suva/Suva134a.html My functions for calculating the liquid density...
  6. A

    Vapor pressure, its decrease and subsequent lowering of boiling point

    I gather the following: - A decrease in atmospheric pressure leads to a decrease in boiling point - Thermodynamics explains this using mathematics - A kinetic theory model can also be used to explain I need to know: - The science behind this occurring. Why does a lower atmospheric...
  7. D

    Chemistry Estimating Vapor Pressure and Vapor Mole Fraction

    1. Homework Statement The normal boiling points of benzene and toluene aer 80.1C and 110.6C, respectively. Both liquids obey Trouton's rule well. For a benzene-toluene liquid solution at 120C, with the molar fraction of benzene in the solution equalling 0.68, estimate the vapor pressure...
  8. U

    Calculating Vapor Pressure Above Ethanol at 35°C

    Homework Statement Calculate the vapor pressure above liquid ethanol at 35 degrees C. The density of liquid ethanol at this temperature is 0.7767 kg/dm^3 and the true vapor pressure is 100 torr. Homework Equations K=P'/P , P'=vapor pressure, P=total pressure Antoine Equation: log P=...
  9. A

    Can Gasoline Vapor in Sewers Lead to Explosions?

    Hi, i need to know something about the explosion risk of gasoline. I have to assess the risks of gasoline leaking into a sewer. They say the vapor can cause explosions. I looked up some facts, but i can't find the answer. 1) Here's the data temperature: 2 to 10°C explosion boundaries of...
  10. S

    Vapor vs Gas, both containing solids

    I'm currently having a discussion with a guy that absolutely says that vapor and gas are the same thing, and they both contain solids, and that's how we see them. I suggested maybe the evaporated vapor that comes off gasoline as you pour it wouldn't have any solids in it, to which he said I'm...
  11. R

    Question on finding the volume of vapor and the volume of liquid

    Homework Statement On a hot 35 degrees celsius day you perspire 1.0 kg of water during your workout. A) what volume is occupied by the evaporated water? B) By what factor is this larger than the volume occupied by the liquid water? Homework Equations PV=nRT PV=NKbT density of water...
  12. P

    Thermodynamics water/water vapor question

    I am having problems with a Thermodynamics question: I am struggling to work out why the meniscus would move up at all. Surely its maximum height is the height of the meniscus at the very beginning when all of the water is liquid? Once the water is added, some evaporates as the...
  13. D

    How Do You Calculate the Vapor Pressure of Water at Different Temperatures?

    Homework Statement The vapor pressure of water at 25.0 C is 23.8 torr, and the heat of vaporization is 43.9 kJ/mol. What is the vapor pressure (atm) of water at 59.8C?Homework Equations Clausius-Clapeyron equation. ln(P2/P1)=(ΔH/R)((1/T1)-(1/T2))The Attempt at a Solution P2=? P1=23.8 torr =...
  14. J

    True Statements on Vapor Pressure

    Homework Statement Which of the following are true statements ? There may be more than one answer a) Volatility of a liquid increases with increasing temperature b) The equilibrium vapor pressure of a liquid results from evaporation exceeding condensation c) The equilibrium vapor...
  15. Z

    Problem on vapor pressureI'm stumbled

    This problem really got me. Take the vapor pressures of pure benzene and pure toluene to be 103 and 32 mm Hg. resp. The pressure on a mixture of 1 mol benzene and 1 mol toluene is reduced until half of the mixture is vaporized. What is this pressure and what are the mole fractions of the...
  16. P

    Constant C in Vapor Pressure Equation

    I'm working on vapor pressure for my general chemistry class, and I recently came across the curve P=C^(-\DeltaH/RT). I was wondering what the units are for C (or are there no units because it is a constant?) and where I could find a table of values for common liquids (water, ethanol, methanol...
  17. E

    Expansion Work in Combustion Reactions: Liquid Water vs. Water Vapor

    Expansion Work -- Still confused. This is more of a general question regarding thermodynamics. If you have a combustion reaction, and it produces either liquid water or water vapor--which case results in higher expansion work? My enthalpy calculations show higher PV work for the reaction with...
  18. G

    Increasing vapor pressure in water

    Why does adding salt to water increase the vapor pressure? Does increasing the volume of water increase the vapor pressure?
  19. D

    Dryness factor / vapor quality relation to Pressure

    Hey guys! Just wanted to inquire about the following relationship. Given a boiler and all the water content inside is above boiling point. Would the dryness factor (vapor quality) decrease or increase with pressure reduction. Example we start at 500 kPa then move down down to 400 kPa. Would the...
  20. C

    MWCNT water vapor amount question

    In order to grow MWCNTs I need to have certain content of water vapor dissolved in the argon gas. The amount of water vapor can be changed with temperature of the water that argon bubbles through. I have Argon entering a flask with water in it. The flow of the argon is 120 ml per min. It makes...
  21. Z

    Calculating Vapor Pressure problem

    Homework Statement A handbook lists the normal boiling point of isooctane, a gasoline component as 99.2°C and its enthalpy of vaporization as 35.76 kJ/mol. Calculate the vapor pressure of isooctane at 25°C. Homework Equations The only equation that makes sense to use for me is the...
  22. K

    What is the entropy change of ice to water and water to vapor?

    1.) What is the entropy change of a 33.0 g ice cube that melts completely in a bucket of water whose temperature is just above the freezing point of water? (J/deg) 2.) What is the entropy change of a 7.3 g spoonful of water that evaporates completely on a hot plate whose temperature is...
  23. H

    How do I make a saturated vapor vessel?

    I have been trying to create a 100% saturated steam (no N2) environment, which should not be too hard but so far I have been puzzled by my observations. For this I have obtained a vacuum vessel (1 ft high by 1 ft diameter cylinder) and a roughing vacuum pump. I have instrumented a pressure...
  24. M

    Vapor of a volatile substance in equilibrium with a fluid

    Hey! I'm in a research group in Gothenburg and we're planning a study with volatile anaesthetics. The problem is as follows: In the clinical setting (operation room) this volatile anaesthetic is administred as a volume% of the inhaled gas. What we're going to do is take a part of this...
  25. B

    Hg vapor energy levels & Frank-Hertz experiment

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  26. J

    Colligative properties: vapor pressure with an electrolyte

    I'm trying to figure out how an electrolyte affects vapour pressure in a solution. My book (Chang chemistry) only lists the formulas for osmotic pressure, boiling point and freezing point. I guess Raoult's law would be something like: P_{1}=i X_{1} P^{1}_{o} Sorry for not respecting the...
  27. S

    Vapor Pressure Help: Solving \DeltaHvap w/ Assumptions

    Hello all I completed a lab last week where we filled a graduated cylinder up 90% of the way with water and inverted it into a water bath and then we heated the bath to 80 degrees Celsius then measured the volume of the air bubble as it cooled to 50 degrees Celsius and at 1 degree Celsius...
  28. fluidistic

    Question about mercury's vapor pressure

    Hi, I've seen a very very small drop of mercury in a little corner of a laboratory table and it likely dates from a whole year. I've been told that mercury is quite volatile. So I shouldn't have seen this little drop if it really dates from the past year. Looking into wikipedia, I see that...
  29. W

    Seeking Peer-Reviewed Studies of Water Vapor Feedback

    One of the key factors in determining the climate sensitivity to the increasing atmospheric concentration of CO2 and other long lived greenhouse gases is the response of water vapor to the relatively small warming induced by these gases. Climate models produce a strong signal of positive water...
  30. B

    Lasers increasing vapor to superheated steam

    I am trying to wrap my head around what it would take to bring water vapor to superheated state. It seems that if you had a vapor stream and shot it with continuous laser energy (CO2 or other gas laser) you could instantly create a high quality steam. I am teetering between buying a diode...
  31. B

    Calculating mass of vapor from vapor pressure

    Homework Statement An open vessel containing water, benzene, and mercury stands in a laboratory measuring 5.0 m by 5.0 m by 3.0 m at 25 degrees C. The vapor pressures are 3.2 kPa, 13.1 kPa, and 0.23 Pa, respectively. What mass of each substance will be found in the air if there is no...
  32. R

    Calculating the composition of vapor in mass percent

    Homework Statement Here's the question form the text. (I have the answer, but don't know how to do part c. "A solution contains 50.0g of heptane (C7H16) and 50.0g of octane (C8H18) at 25 C. the vapor pressures of pure heptane and pure octane at 25 C are 45.8 torr and 10.9 torr...
  33. A

    Thermodynamics: Water vapor vessel plunged into water ice bath

    Homework Statement A closed rigid vessel contains 0.1 kg of water vapor (steam) at 1 bar and 200 C. The vessel is plunged into a bath containing water and ice. After the vessel cools and reaches equilibrium with the bath, the bath still contains water and ice. a. What is the volume...
  34. V

    Vapor pressure question in chemical thermodynamics

    Homework Statement Calculate the vapor pressure of iso-propyle alcohol over iso-propyle alcohol in pure liquid state at 298,15K. Homework Equations A possible equation to solve this problem, I think, would be to use this formula put together by two definitions of free energy. \Delta G...
  35. M

    Freezing Point Depression and vapor pressure

    Why is the vapour pressure lowered when non volatile solute is added to a solvent? What is the physical reason? Also, why do binary solutions freeze over a range of temperatures, not at one specific temperature? Thanks guys, as usual, for sharing the knowledge!:smile:
  36. J

    Vapor Pressure Saturation in Air Collection: Estimating Water Vapor Mass

    Homework Statement "Suppose you were to collect 1.0 L air by passing it slowly thorugh water at 20C and into a container. estimate the mass of water vapor in the collect air, assuming that the air is saturated." I don't know where to even begin. at first i thought it had something to do...
  37. M

    Why Does a Sodium Vapor Lamp Create a Dark Line at 589nm in the Spectrum?

    Homework Statement i understand that the wavelength given off by a sodium vapor lamp is 589nm, is this why there is a dark line in the continuous spectrum at 589mn? Homework Equations The Attempt at a Solution
  38. B

    What is the vapor pressure of a solution containing glucose and water at 60.0C?

    Homework Statement What is the capor pressure of a solution containing .15 mol of glucose (C6H12O6) and 1.65 mol of water at a temperature of 60.0C? the vapor pressure of pure water at this temperature is 149.38 torr Homework Equations Ralout's law? P=PoX The Attempt at a...
  39. A

    Vapor Pressure of Benzene at 50°C: 0.028 mmHg

    Homework Statement Benzene, C6H6, has a boiling point of 80 degrees Celsius. The density of benzene vapor in equilibrium with liquid benzene at 50 degrees Celsius is 1.153 g/L. What is the vapor pressure of benzene in mmHg at 50 degrees Celsius? Homework Equations PV=nRt density = m/v...
  40. T

    Vapor Comression Refrigeration cycle

    I am doing a project for my thermodynamics class and we have to choose a compressor for a a vapor compression refrigeration cycle that has a heat transfer rate of 1500 btu/h and must maintain 0F in the freezer when the room temp is 90F. I have went through some calculations to find the mass flow...
  41. Z

    Understanding Vapor Pressure Laws for Astrophysics

    So, I'm new to astrophys, and I'm having trouble making a model because I don't think I understand an equation. It's a vapor pressure law, and it says it takes the form of log(pressure) = A-(B/T) T is in kelvins, A is 10.6, and B is 13500. Apparently pressure ends up being dynes/cm^2...
  42. T

    Vapor density in kg/m3 in CO2 absorber

    hello all, I got a bit of a problem. I want to calculate the vapor density (kg/ m3 or lbs/ ft3) with the following facts: temp: 40C pressure : 20-31 bar flow rate: 1000-10000 kmole/ hr MW avg: 10-12 g/ mol (it is a mixture of H2, CO, CO2, CH4, H2O)> mostly H2 I wanted to know which...
  43. M

    Vapor Pressure of Hg in a 10m x 10m x 3m Lab

    The vapor presurre of mercury is 0.00185 mmhg at 25 degree C. A single drop of Hg(0.1 mL) is spilled in a laboratory of dimensions 10m x 10m x3m. Does the entire drop evaporate? What is the partial pressure of Hg in the laboratory? (Use 13.6 g/ml for the density of Hg.) (b) The normal boiling...
  44. S

    Vapor Pressure of Toulene @ 190°C for Cavitation Issue

    I am looking for the vapor pressure of Toulene at 190 deg Centrigrade to solve the cavitation problem with one of my pumps. Can anyone guide in this regard...
  45. G

    Vapor pressure of a liquid homework

    [SOLVED] vapor pressure Homework Statement the vapor pressure of a liquid at 25 degrees celcius is 200 torr. If the pressure over the liquid is lowered to 190 torr at 25 degrees celsius the liquid will... a)evaporate b)boil c)freeze Homework Equations The Attempt at a...
  46. F

    How Does Temperature Affect Ethanol Vapor Pressure and Mass?

    A 4.7-L sealed bottle containing 0.33 g of liquid ethanol, C2H6O, is placed in a refrigerator and reaches equilibrium with its vapor at -11 degrees C. a) What is the mass of ethanol present in the vapor? b) When the container is removed and warmed to room temperature, 20 degrees C, will all...
  47. C

    Calculating Vapor Pressure of Pure Liquids: A Guide

    i have a question, is there a way to calculate the vapor pressure of a pure liquid when just given a formula a total vapor pressure and a temp? thanks for the help.
  48. C

    Vapor pressure of Thallium Iodide.

    I've tried looking everywhere but cannot find much information on the vapor pressure of TlI. I'm not very well versed in chemistry, so if I'm missing something obvious please let me know, I'm interested in how the vapor pressure changes from room temp up to something like 600K. I've found...
  49. O

    2 slit trouble with vapor trails

    This seems to be worth doing, but maybe I don't understand vapor trails. Is it possible to get a two slit interference pattern from a particle that makes a vapor trail? If so could you get the interference pattern and then change the conditions inside the chamber so that a vapor trail was...
  50. T

    What is a vapor bulb thermometer ?

    What is a "vapor bulb thermometer"? The problem statement vapor bulb thermometer I'm simply looking for a definition. I haven't been able to find it on the internet. Before looking in a library, I was wondering if anyone knows which book to look for, or where on the internet a definition...
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