What is Vapour: Definition and 95 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. K

    How to Calculate Vapour Pressure Changes with Temperature?

    Homework Statement This is problem in Mandl's book on Stats Phys; The vapour pressure of water at 298.15 K is 23.75 mmHg. What is the vapour pressure of water at 273.16 K, given that the latent heat of evaporation of water at 298.15 and 273.16 K is 43,991 and 45,049 J/mol respectively?Homework...
  2. Z

    Detemining the mass of water vapour in air (Ideal gas law)

    1. I am supposed to calculate the mass of water vapour in one cubic meter of air that has a relative humidity of 80% at 20°C. 2. p[v] = (eM[w]) / (RT) Where: p[v] = vapour density e = water vapour pressure M[w] = molar mass of water R = gas constant (8,314 J / (mol*K)...
  3. A

    Understanding the Work Required to Compress Water Vapor at 200 atm

    Okay my exercise says the following: "By applying a pressure of 200 atm, you can compress water to 99% of its usual volume. Find the work needed to do this." Now I'm having a bit of trouble with how this is put. For me it doesn't make sense to just put 200atm pressure on normal pressured...
  4. A

    Vapor Pressure: What Affects Gasoline Evaporation?

    Hi all, I have a question on vapor pressure. As far as I understood, a liquid will flashes into gas when the absolute pressure it is experiencing (in a pipe / in the atmosphere) is lower than the liquid's vapor pressure (assuming temperature is constant). Everyone knows that gasoline forms...
  5. D

    [Help] Expansion of air or due to formation of water vapour?

    Hi all, I recently encountered this scenario. I placed a (1 litre) glass bottle with water (about half filled) that is corked up near my stove. My wife was cooking and the cork suddenly popped. We discussed this over dinner and I said that it was due the air in the bottle that has...
  6. N

    Determing vapour pressure experimentally - how?

    Homework Statement I am supposed to determine the vapour pressure experimentally of a series of prepared solutions, which are a mixture of 2 different substances in different proportions. This involved attempting to create a "vacuum", placing the liquid inside and then measuring the change in...
  7. A

    Question about Critical Temperature and Interface between Liquid and vapour

    While Studying 'surface tension' I came across a statement that 'At critical Temperature the interface between liquid and its vapour disappears' without any explanation or logic. Can Anyone please tell me why such phenomenon is observed at critical temperature ? Thanks in Advance.
  8. Z

    Lowering of Vapour Pressure - a C.P ?

    Is lowering of vapour pressure a colligative property? I tried proving this and found it to be true. Pa = Poaχa, where a=solvent and b=solute Substituting χa=1-χb and some rearranging, we get Poa-Pa=Poaχb As Poa is constant for a given liquid at a given temperature, lowering of...
  9. S

    How much would the earth heat up if all water turned to vapour?

    We have 1.400.000.000 km³ water which would become 2.24E12 km³ of water vapour. Does anyone know how much the Earth would heat up due to the greenhouse effect of all this vapour?
  10. H

    Atmosphere, carbon dioxide and water vapour help?

    atmosphere, carbon dioxide and water vapour help?? (c) One cubic metre (1 m3) of atmosphere at sea level contains 3.80 × 10(power of)2 ppm of CO2 and 5.00 × 10(power of)3 ppm of water vapour. If there is a total of 2.6 × 10(power of)25 molecules in 1 m3 of air, calculate how many...
  11. A

    Fringe pattern of a vapour lamp

    Homework Statement Hi Please, what fringe pattern would be obtained with a sodium vapour lamp? Homework Equations The Attempt at a Solution I am guessing that a dominant yellow colour would be obtained. The sodium is almost acting like a monochromatic light and therefore has a...
  12. P

    Dependance of saturated vapour preassure of external preassure

    I'm interested in an equillibrium state between pure liquid (e.g. water) and its vapour preassure mixed with other gases (e.g water vapour in the atmospheric gases). I would like to compute the dependence of vapour saturated preassure on the total preassure of the system (vapour partial...
  13. 5

    Why is the Vapour pressure of Water Constant ?

    Now if i have the vapour pressure of water to be 200mm and the water occupies 4 L out of 20 L closed vessel.Which implies that the Vapour occupies 16 L Now if i shift the water to a 30 L closed vessel.The vapour pressure of water vapour remains the same even though it occupies a greater volume...
  14. R

    Vapour pressure and volatility.

    Homework Statement (I)Explain how each of the following factors affect the vapour pressure of a liquid: (a)surface area, (b)volume, (c)attractive intermolecular forces, (d)temperature, (e)density of liquid. (II)Order the following substances in terms of volatility: CH4, CBr4, CH2Cl2, CH3Cl...
  15. G

    Thermodynamics - Vapour Power Plants

    Homework Statement A compressor takes in 4 kg/s of air at atmospheric pressure and temperature, 1 bar and 25 degrees C. Air leaves the compressor at 4 bars and 200 degreesC. Calculate the power input to the compressor and its isentropic efficiency. For air Cp=1.005 and Cv=0.718 kJ/kg K...
  16. T

    Osmosis, osmotic pressure, vapour pressure

    Why does osmosis happens? Does osmosis happens when we have osmotic pressure difference between the two solutions (that are connected by a membrane)? Does osmosis happens when we have two solutions of different concentrations? My professor told that osmosis happens because of the vapour...
  17. P

    Diamagnetic vapour + electromagnetic grid

    I know, I know. I didn't fill out the thing. But I don't really have a 'problem' to solve, I'm just looking for some vague theoretical speculation... I'm a new media art student and I'd like to use a grid of electromagnets to undulate a layer of low-lying fog (which would be glycerin +...
  18. D

    Vapour Liquid Equilibrium for a two component mixture.

    I am studying vapor liquid eqilibrium for two component systems. There are some things which confuse me right now. These are the questions: - (1) Since there has to be atleast one phase, the degrees of freedom are maximum three. Which means, the degrees of freedom are P, T and composition...
  19. H

    Why can't sodium vapour lamp be used in spectrometer experiment

    i was working with a spectrometer and the aim of the experiment was to find the refractive index of a prism for various colors. i was asked specifically to use mercury vapor lamp and was insisted not to use sodium vapour lamp. why is it so?
  20. J

    Mean Free Path of an Electron in Mercury Vapour

    Homework Statement Estimate the mean free path of an electron in mercury vapour at a temperature of 160 degrees C, where the vapour pressure is 11.28 mmHg It gives the standard atmospheric pressure as 761.84 mmHg. Homework Equations Mean free path= (Boltzmann's constant times...
  21. N

    Vapour Pressure & Liquid Phase: Explained

    If the vapour pressure of a component is bigger than the system pressure, does it means it will fully in vapour phase and no liquid phase are formed??
  22. L

    Vapour pressures of Propanal and propanoic acid

    Hi, I am looking for more information on vapour pressures of propanal and propanoic acid at room tempreature and need to explain in in terms of molecular structure. Couldn't find any thing on it though.
  23. T

    Why there is vapour in Dry CO2

    Homework Statement Hi there, could anyone help me pls. I want to show my sons kinder class what happens when you put Dry Ice (solid CO2) into water but would like to know for them and for me what the actual process is when it sublimates. I don't understand why there are so many bubbles or...
  24. R

    CO2 vapour pressure passed critical temperature

    I've been looking at phase diagrams and vapour pressure tables for CO2 and i notice that the data stops at the critical point. what would happen to the pressure of CO2 if I heated it to above the critical temperature and kept the volume constant? Would the pressure increase following the...
  25. K

    Volume vapour calculation for jet fuel a1

    [b]1. Homework Statement is there any formulae for obtain the volume vapour % V/V. we have a jet fuel a1 10 liters in the closed chamber.the temperature measured inside is 41 degree. we want to know how much vapour it can generate at the particular temperature. we have the following data 1...
  26. G

    Vapour pressure problem (simple)

    The vapour pressure of pure chloroform at 70.0oC is 135.7 kPa. What mass of iodine (I2) should be dissolved in 1 L of chloroform, CHCl3 (density = 1.49 g/cm3) to lower the vapour pressure by 13.3 kPa? hey guys i really can't do this question, i think in involves raults law, P=XPA anyhelp...
  27. M

    Question on water vapour and pressures

    Homework Statement 20 litres of moist air at 25 degrees celsius with a relative humidity of 75% are compressed isothermally to a volume of 4 litres. Calculate the mass of water condensed? (One method, find the original water vapour pressure, it will be increased by what factor?) Homework...
  28. P

    Clouds are water liquid, not vapour, why it don't fall down?

    Title says all, why clouds are up? have the air more density than water? Thanks!
  29. E

    Calculations using Saturated Vapour Pressure

    Hi all, new here, so don't know if this is the right place. All the other places in the forum seemed like advanced stuff! Anyway, i don't understand why when calculating the partial pressure of a gas in SVP conditions, you subtract 6.28kPa from the normal atomospheric pressure of 101.1kPa...
  30. T

    How Does Introducing Gas into a Torus Affect Vapour Pressure?

    Hi... I found this site a lot time ago and sometimes I feel like viewing your problems, maybe in a future I'll be active... I want to say that this IS NOT an homework, but it's an exercise I was never able to solve and so I try to put it here, even if I don't know whether it is the right section...
  31. E

    Vapour Pressure| Boiling| Atmospheric P

    Ok I do not get WHY an object boils when atmospheric pressure is equal to Vapour pressure. Can anyone explain this? In my textbook it doesent explain it at all.
  32. K

    HELP A question on vapour pressure

    HELP!A question on vapour pressure Homework Statement The vapor pressure of dichloromethane, CH2Cl2, at 0 degree Celsius is 134 mmHg. The normal boiling point of dichloromethane is 40.0 degree Celsius. Calculate its molar heat of vaporization. Homework Equations The Attempt at a...
  33. R

    Plexiglas (PMMA) Vapour Pressure: Seeking Info

    Hi everybody. I would like to know the value of vapour pressure of plexiglas (PMMA) at ambiant temperature. For the time being I've not found that characteristic on the net.
  34. B

    Airborne dust, water vapour and global warming

    More dust in the air presumably means that there are more nuclei on which water molecules can condense to form liquid water.Water vapour is a greenhouse gas so can the current trend in global warming be attributed to less dust in the air than usual resulting in more water vapour and higher...
  35. S

    How do you calculate partial pressure of water vapour in air?

    How do you calculate partial pressure of water vapour in air??
  36. P

    What is the difference between gas and vapour?

    what is the difference between vapour and gas? when gas condence it change in liquid...so what difference between gas and vapour?
  37. Z

    Calculating Heat & Work Done in Ice to Vapour System

    I realize that there has been a post recently concerning this sort of thing but i think it went a bit off topic for me to follow. :) The question is Consider a bowl containing 1 mol of ice at a temperature of -10C and atmospheric pressure. The sample is heated very slowly to 115C. Split the...
  38. G

    How does a vacuum pump cause water to turn into ice in a closed flask?

    Homework Statement Water at room temperature is placed in a flask connected by a rubber tubing to a vacuum pump, and the pump is turned on. Ater several minutes, the volume of the water has decreased and what remains has turned to ice. Explain The Attempt at a Solution This is the...
  39. H

    Density of water vapour in the air following compression if it were an Ideal Gas

    Density of water vapour in the air involving compression Homework Statement A volume Vi = 23.2 L of air at temperature T = 22 °C is compressed at constant temperature to a volume Vf = 11.0 L. The relative humidity of the air before compression is H = 59.4 %. The saturated vapour pressure of...
  40. A

    It takes an input of energy to convert liquid to vapour ,so increse

    it takes an input of energy to convert liquid to vapour ,so increse the entropy if an increase in entropy is natural, why does this not happen naturally with less effort on its own?
  41. S

    Magnetic permeability of water vapour

    Searched all over, still could not find the magnetic permability of water vapour. Please help!. email me at shellysharma@yahoo.com if you know the value. Thanks for your time!
  42. H

    Vapour Pressure and External Pressure

    When the vapour pressure of a liquid equals to the external pressure, the liquid will boil. So, what if a liquid is placed in a vacum? Will the liquid boil instantly when heated?
  43. R

    Water vapour overlooked as greenhouse gas ?

    Hello all It seems that water vapour doesn't figure in greenhouse gas calcs & global warming. This site claims.. "Water vapor overwhelms all other natural and man-made greenhouse contributions." http://www.clearlight.com/~mhieb/WVFossils/greenhouse_data.html Are they right ? cheers
  44. Amith2006

    Solving the Temperature of a Mercury Vapour Lamp

    Sir, The question is as follows: If excitation energy is provided by inelastic collisions between molecules, what is the temperature at which mercury vapour lamp will emit Ultra violet light of wavelength 2586 Angstrom? I tried applying Wein's displacement law(lamda * T =...
  45. E

    How Does Surface Curvature Affect Saturation Vapour Pressure?

    The pressure exerted by a saturated vapour depends on the temperature and the curvature of the liquids surface. Why does it depend on the curvature of the liquids surface?
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