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. J

    Vapor Pressure and non ideal gases

    Hi, I understand that vapor pressure is independent of initial pressure, and depends only on temperature. However, is this true of a non ideal gas at high pressures? (I am specifically interested in the vapor pressure of a meg/water mixture at approx. 100 bar), Thanks
  2. maistral

    Cubic EoS - only VAPOR root is converging o_o

    Hello. I would like to inquire as to how to deal with the said topic title. I'm trying to generate a VLE graph for ethylene oxide-water. While I know that EO will quickly vaporize since the boiling point of EO is quite low, I'm still trying to generate a VLE using SRK. So while the vapor...
  3. A

    Calculating Water Vapor Requirements for Temperature Change of a System

    Homework Statement How much water vapor (100 ° C) should be added to 120 g of ice (0 ° C) so that the final system has a final temperature of 35° C. Homework Equations Qvapor = lvapor * mvapor during condensation, where lvapor =2260 kJ/kg Q1 = cwater*mvapor*ΔT during cooling, and...
  4. S

    Medical (Respiration) how water vapor affects barometric pressure

    hello folks, let me apologize if this was addressed before, but every time I try to search for partial pressure of oxygen and water, I get problems unrelated to mine. I also searched Wikipedia and Google and found their explanations a bit too obtuse. But it's possible I'm just doing a bad job...
  5. B

    Vapor Pressure, Open Container, and Boiling

    I've been confused about this for a while now and haven't found anything that directly addresses this problem. Please correct any faults you see in my reasoning. My understanding of vapor pressure is that it is the pressure exerted by the vapor phase of a substance above the liquid phase...
  6. aleksbooker

    How do you calculate density of a vapor only vapor pressure and temp.

    Hello all, The question given is: Mercury and many of its compounds are dangerous poisons if breathed, swallowed or even absorbed through the skin. The liquid metal has a vapor pressure of 0.00169mmHg at 24 degrees Celsius. If the air in a small room is saturated with mercury vapor, how many...
  7. marcus

    Water vapor observed venting from Ceres

    http://www.bbc.co.uk/news/science-environment-25849871 Herschel space telescope press release: http://sci.esa.int/herschel/53125-herschel-discovers-water-vapour-around-dwarf-planet-ceres/ Abstract of scholarly article published in Nature...
  8. Q

    Solving a Vapor Pressure Problem: Find Hydrogen Volume at 23°C

    Homework Statement A 425-mL sample of hydrogen is collected above water at 35°C and 763 torr. Find the volume of the hydrogen sample when the temperature falls to 23°C, assuming the barometric pressure does not change. (vapor pressures of water : at 35°C, 42.2 torr ; at 23°C, 21.1 torr)...
  9. Q

    How Much CCl4 Remains Liquid at Equilibrium in a Sealed Flask?

    Homework Statement If 5.00 mL of liquid carbon tetrachloride (CCl4, density = 1.587 g/mL) was injected into a sealed 5.00 L flask at 30.0°C, what volume (if any) of the CCl4 would remain as liquid after equilibrium is reached? (the vapor pressure of CCl4 at 30.0°C is 143.0 mmHg) Homework...
  10. Q

    Vapor Pressure and Raoult's Law

    Homework Statement The vapor pressure of pure water at 45 degrees C is 71.9 mm Hg. What is the vapor pressure when 18g of sucrose (MM = 342.3g/mol) is added to 82g of water? Homework Equations VP of solution = mole fraction of solvent * VP of pure solvent The Attempt at a Solution...
  11. Q

    How Does Raoult's Law Apply to Calculating Vapor Pressure in Solutions?

    Homework Statement http://i.minus.com/juL6gvGzvWdm.png Homework Equations Raoult's law: Pressure of solution = Mole fraction of solvent multiplied by vapor pressure of pure solvent. We're assuming non-volatile solutes. The Attempt at a Solution My solution...
  12. LunaFly

    Vapor Pressure Curve on the PVT Diagram

    Hi all, I am wondering about where the vapor pressure curve would be located on the PVT surface of a substance. I know that as the temperature of a liquid increases, its vapor pressure increases. This continues until the vapor pressure is equal to the atmospheric pressure, at which point...
  13. Z

    Fraction of vapor present in an ideal solution

    Suppose A and B form an ideal solution under a piston. The vapor pressure of pure A is 300 mmHg and that of pure B is 800 mmHg (at the same temperature). If the piston maintains 700 mmHg, what fraction of vapor is present in a 40 mole% A and 60 mole% B mixture. The answer is "there is no...
  14. M

    How Does Pressure Remain Constant During a Phase Transition?

    In reference to the graph at the bottom, my textbook has a statement '''..A process of vaporization or condensation at a constant temperature is illustrated by the lines G-H-I or I-H-G, respectively, in figure 16.3. Water would vaporize or condense at a constant temperature as the...
  15. Z

    Archived Vapor composition from bubble-point temp.

    Suppose you have a mixture of 30 mol% pentane and 70 mol% hexane at 1 atm and 60oC. If the Tbubble-point = 55.1oC, calculate the composition of vapor of the first bubble as the mixture is heated. I found p*pentane = 1392.95 and p*hexane = 484.96 using Antoine's equation with T = 55.1. Now I...
  16. D

    Gas, vapor, clouds any difference?

    Gas, vapor, clouds ... any difference? "Most of the water in the atmosphere is in the gas state called water vapor." (http://www.srh.noaa.gov/srh/jetstream/atmos/ll_rainman.htm) This quote was taken from a site dealing with weather. Does this mean that the average temperature of the...
  17. J

    Vapor pressure + air pressure?

    Hi, could someone please tell me if the vapor pressure should be combined with the air pressure in a sealed vessel to give the total pressure? For example, if I put room temperature water in a test tube (at sea level) with some head space for air and then seal it, the pressure inside would be 1...
  18. C

    Latent heat in water vapor below boiling

    Hi - I'm a physics newbie so this is an elementary question, but I can't find the answer with a google search. Water evaporates at a wide range of temperatures, what is the latent heat in the water vapor (in calories or Joules), for example, at 30°C, 60°C? Assume standard atmospheric...
  19. J

    Predict which of the solutions below will exert the highest Vapor pressure

    Homework Statement Hi I have a question. Predict which of the solutions below will exert the highest Vapor pressure O2 in HOH NH3 in HOH and CH3OH in HOH Homework Equations I drew them out. So I know that CH3OH HOH exhibits h bonding. So does NH3 HOH I was wondering about O2...
  20. R

    How to find water vapor volume at different pressures than atm?

    Homework Statement If a known amount, let's say 300 liters of water gas (water vapor) is flowing from an atmospheric (14.7 psi) source/chamber, into a chamber of reduced pressure of 10 psi, does the volume amount and/or moles change? Homework Equations So I believe I would multiply the...
  21. S

    Heat of solution and vapor pressure

    I am having trouble with the relationship between these two. My book says that negative heat of solution forms stronger bonds and lowers vapor pressure and positive heat of solution forms weaker bonds and raises vapor pressure. Shouldn't vapor pressure be higher for negative heat of solution...
  22. J

    Does atmospheric pressure affect the saturated vapor pressure ?

    When the Clausius-Clapeyron equation for saturation vapor pressure over liquid water is derived via the Carnot cycle, it is usually assumed that there is only gaseous water above the liquid. The other atmospheric gases are neglected. However, in common settings (lake, glass of water...), the...
  23. S

    Vapor pressure and atmospheric pressure

    the book says vapor pressure is independent of atmospheric pressure, if that is the case then why must the vapor pressure of a liquid be equal to the atmopheric pressure for it boils. I pictured atmospheric pressure as a column of air sitting above a liquid and therefore pushing down the gas...
  24. S

    Vapor pressure of boiling water

    Why does the answer say that vapor pressure only depends on temperature and intermolecular forces substance experiences? I thought external pressure did affect vapor pressure because when you heat a pot of boiling water at higher elevation the boiling point decreases, and vapor pressure...
  25. M

    Can vapor condensation cause significant drop in vapor flow rate?

    Need some help here! My plant just installed a water scrubber for controlling methanol emissions. Results obtained from stack tests have consistently shown the flow rate of the gasses from the scrubber outlet is about 30% of gas flow rate into the scrubber. From process knowledge, most of the...
  26. J

    Complicated liquid to vapor conversion problem

    I had a question about the volume of vapor produced from an amount of liquid after increasing the pressure inside a container containing the liquid, then rapidly decreasing it back to the original pressure. Say you have an amount of water, say 1mL (or another liquid, not sure what descriptors...
  27. N

    Is boiling just high vapor pressure?

    Is boiling basically a really high vapor pressure?
  28. R

    How are the satellites that detect water vapor made?

    How are the satellites that detect water vapor made? What goes into them that allow companies such as NOAA to create those water vapor images?
  29. P

    How is saturation pressure different than vapor pressure?

    I think I understand, but I want to make sure. The vapor pressure of a substance is the pressure of the substance evaporating/sublimating at a given temperature and can be calculated using the Antoine Equation. This must be measured at the interface of the substance and atmosphere, or if the...
  30. K

    Photoelectric effect, mercury vapor lamp

    I had a lab with photoelectric effect and we measured different colors wavelength/frequency by finding stopping voltage vs current. Then we used no color filter and used the mercury vapor lamp and had to find the wavelength which was around 400nm. Questions were why was this wavelength the...
  31. 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...
  32. D

    Amount of CO2 vaporized in a phase change from liquid to solid & vapor

    Homework Statement Saturated liquid CO2 is at T= 293 K and P=5.72*10^6 Pa and undergoes throttling to P=1.01*10^5. The resulting solid and vapor mixture is at T = 195 K. What fraction of the carbon dioxide is vaporized? (The enthalpy of the saturated liquid in the initial state is 24,200...
  33. jaumzaum

    Liquid-Vapor Equilibrium and Vapor Pressure

    I'm studying vapor pressure and I'm having trouble to understand some concepts. Vapor pressure depends only on the temperature of the liquid in question right? For example, if we have a container with water at 30° C, it doesn't matter the experiment, would it ALWAYS be a vapor phase with...
  34. D

    Irreversible Carnot Vapor Power Cycle

    Two questions: 1. What does the T-s diagram look like for the irreversible cycle? 2. Do the isentropic efficiency equations that you apply to turbines and compressors (especially in the Rankine cycle) apply to the theoretical "turbines" and "pumps" in the Carnot cycle?
  35. M

    Thermodynamics - Saturated Vapor Quality Question

    Homework Statement A 4 cubic meter rigid vessel contains 0.04 cubic meters of liquid water and 3.96 cubic meters of water vapor at 101.325 kPa. What is the quality of the saturated vapor? Homework Equations Specific volume of saturated liquid at 100 C and 101.325 kPa: 0.001044 m^3/kg...
  36. S

    Vapor Pressure Measurement Problem

    Hi all, Just have a quick question regarding the measurement of vapor pressure. Firstly, let me explain my scenario. I am carrying-out some measurements of steam condensation in a vacuum. The steam is being condensed in a air-cooled heat exchanger. Initially, I let in a quantity of steam...
  37. S

    Vapor Pressure in Condensing Steam System

    Hi all, Just have a quick question regarding the measurement of vapor pressure. Firstly, let me explain my scenario. I am carrying-out some measurements of steam condensation in a vacuum. The steam is being condensed in a air-cooled heat exchanger. Initially, I let in a quantity of steam...
  38. skate_nerd

    How would water vapor contamination affect PV=nRT

    Homework Statement Doing a lab here, but were kind of stuck. This lab is meant to experiment the formula PV=nRT, and the set up is a canister of CO^2 with a fixed volume that has a pressure sensor connected to it reading in pascals. We heat up the CO^2 by placing the canister in a beaker of...
  39. F

    Separate water vapor from atmospheric air

    There is a simple method to separate the water vapor from the atmospheric air, however, in the form of gas and not of condensed water?
  40. A

    Question on Vapor Compression Cycle.

    For convenience, let's assume the following process to be ideal. Process 1-2 Isenthalpic compression Process 2-3 Condensation Process 3-4 Throttling Process 4-1 Evaporation The refrigerant is dry-saturated at the end of compression. Here's what I don't understand: During process 2-3, if we...
  41. G

    ChemE: vapor pressure and condensation

    Homework Statement A gaseous mixture containing 0.190 mol fraction of carbon tetrachloride (CCl4) and 0.810 mol fraction of dry air is initially at 62.0°C and 1141 mmHg. If this mixture is cooled at a constant pressure, at what temperature does the CCl4 first start to condense? I already did...
  42. C

    Vapor Pressure and Atmospheric Pressure

    From what I have read so far, the vapor pressure of a liquid is temperature dependent while it is independent of the atmospheric pressure. I am not sure why atmospheric pressure would have no effect of the vapor pressure though. For example, if a highly volatile liquid is placed in a sealed...
  43. M

    I don't understand this Vapor Concept problem?

    Homework Statement If oxygen gas occupies 25mL at -25 'C and 65 mm Hg. What is the volume at 25 'C and 350 mmHg?Homework Equations P1+P2+P3=Ptotal The Attempt at a Solution I am really not sure how to do this :( I think maybe I figured it out. Please see below!
  44. A

    Thermodynamics: Cooling Superheated Water Vapor to Saturated Vapor

    Superheated H20 at 400 kPa is slowly cooled in a sealed rigid vessel until the temperature is measured to be 115 centigrade, when condensation first occurs. What is the Initial Temperature? I know that the temperature and pressure at point two (saturated vapor) can be found in a standard...
  45. M

    Thermodynamics - Saturated Mixture to Superheated Vapor

    Homework Statement A rigid tank contains 5 lb of a two-phase, liquid-vapor mixture of H2O, initially at T = 260 F with a quality of 0.6. Heat transfer to the contents of the tank occurs until the temperature is T = 320 F. Show the process on a p-v diagram. Determine the mass of vapor, in lb...
  46. W

    What the escape rate of water vapor into space?

    I understand that some water vapor escapes into space but what's the amount say per year?
  47. N

    Calculating Vapor Pressure of Water with Desolved Solids

    Hi I'm currently writing a some software for calculating the effects of differant grades of water on Centrifical Pump Purformance i have be able to calculate all the apropiate Pressures, flows, viscositys, density, and pressure loss effects on the pump purformance where I'm having trouble is...
  48. W

    Experiment: Vapor Compression Refrigeration

    i have calculated the coefficient of performance COP for both COP ideal and COP from p-h diagram. But the COP ideal i get is lower than the COP i calculated from p-h diagram. is it possible? please help :)
  49. C

    Calculating Saturation Vapor Pressure?

    I'm trying to find the equations or diagrams for two types of Saturation Vapor Pressures: 1) Pw = Saturation vapor pressure at water temperature 2) Pa = Saturation vapor pressure at air dew point My solution: Relative humidity = (saturation vapour pressure at dew point)/( saturation...
  50. S

    Thermodynamics: Vapor Compression Refrigeration that is Adiabatic?

    Consider a heat pump works on the vapor-compression refrigeration cycle with 0.2 kg/s of refrigerant-134a as the working fluid. The cycle is used to maintain a house at 26oC while absorbing heat from the outdoors at 3oC. R-134a enters the compressor at 200 kPa as a saturated vapor and leaves at...
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