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. I

    Water vapor and air - questions

    Hi.. I'm a pilot and I'm trying to get a better grasp on meteorology. I'm wondering how exactly water vapor is contained in air. I understand it's mostly governed by the temperature of the air but does the temperature of the water affect that? Why is it dependent on the temperature of the air...
  2. T

    Vapor pressure and the boiling point of a liquid

    I'm not totally sure this topic should be placed in this forum, since it is not specifically solid state. Anyways, my question is simply why is there a correlation between vapor pressure and the boiling point of a substance, I would have thought that the boiling point would be at any...
  3. K

    Partial Pressures of an Ideal Gas Mixture Containing Water Vapor

    Homework Statement A gas mixture of 0.13 mol NH3, 1.27 mol N2, and 0.025 mol H2O vapor is contained at a total pressure of 830 mm Hg and 323 K. Calculate the following: (a) Mole fraction of each component. (b) Partial pressure of each component in mm Hg. (c) Total volume of mixture in m3...
  4. Q

    Trying to make fuel vapor supply system

    Originally posted this in the wrong section. What would be the most basic and solid way of doing this for a gasoline engine? I've thought about using a ultrasonic mister but I am afraid that there may be a potential for a spark, don't want to blow up. I've also tossed around the idea of heating...
  5. Q

    Try to make a vapor fuel supply system

    What would be the most basic and solid way of doing this for a gasoline engine? I've thought about using a ultrasonic mister but I am afraid that there may be a potential for a spark, don't want to blow up. I've also tossed around the idea of heating the fuel to its evaporation temps, but not...
  6. T

    Vapor Pressure of a pure solvent

    I know that the vapor pressure of a solvent would decrease with a changing concentration if there was an addition of a solute. However, would the vapor pressure change with a changing concentration of the pure solvent (no solute added)?
  7. M

    Evaporation of a solid in water vapor.

    Can a solid, no matter how small, even a single cell, be evaporated with water vapor from a pool of water?
  8. J

    Entropy of liquid water and water vapor

    Homework Statement 1- Use the thermodynamic table to establish an equation giving the molar entropy of liquid water as a function of temperature. Do the same for water vapor. 2- Use these equations to calculate the entropy of vaporization and the enthalpy of vaporization. 3- From the...
  9. B

    Mass flow in Vapor Compression Cylce HELP

    Hi guys, I'm doing some calculations on a vapor compression cycle system for my Master Thesis. My question is: Does the mass flow change when the refrigerant flows through the (electronic) expansion valve (assuming steady state flow)? I assume that it doesn't but I can't seem to get...
  10. C

    Phase diagram contradiction: why does vapor exist?

    When you learn about phase diagrams of pure substances, you learn that the liquid and gas phases are in equilibrium only along the line separating the pure liquid and pure gas regions. But if you have a sample of liquid in a closed container with some empty space in it, that empty space...
  11. B

    Water + Water Vapor - Can I use ideal gas law?

    Homework Statement Sealed container which is used to heat 200 kg water is initially at 25 degrees C. Since the container is sealed, the water remains in saturated state while its temperature and pressure increases. The remaining volume of the container is filled with water vapor at the same...
  12. G

    Calculating maximum amount of water vapor per unit volume

    Homework Statement Compute the maximum amount of water vapor per unit volume that air can hold at the surface, where Ts = 288 K, and at a height of 10 km where T = 220 K. Express your answers in kg m-3. Homework Equations e_{s}=Ae^{\beta T} e=\rho _{v}R_{v}T The Attempt at a...
  13. S

    Boiling point and vapor pressure

    I am trying to understand the concept of boiling from a very fundamental perspective. Most textbooks say that: as a liquid is heated, it's vapor pressure increases. When the vapor pressure reaches the surrounding pressure(or atmospheric pressure at that point), then boiling occurs. I agree...
  14. S

    Boiling point and vapor pressure

    I am trying to understand the concept of boiling from a very fundamental perspective. Most textbooks say that: as a liquid is heated, it's vapor pressure increases. When the vapor pressure reaches the surrounding pressure(or atmospheric pressure at that point), then boiling occurs. I agree...
  15. Q

    Finding atomic weight from vapor density of metal chloride

    Homework Statement Vapor density of a metal chloride is 66. Its oxide contains 53% metal. The atomic weight of the metal is ? Homework Equations vapor density = 0.5 * molar mass The Attempt at a Solution Using the above formula, I found the molar mass of the metal chloride as...
  16. M

    Water vapor / energy question

    The following is something that puzzles me a bit, and I'd appreciate some insight in the matter. Thank You :) Given the following: A shallow pan with a smaller diameter beaker sitting in it's center Both the pan and the beaker contain distilled water The level of the water in the beaker...
  17. S

    Gas or vapor and a liquid from another liquid using temperature.

    The boiling temperature of a liquid removes as much heat as is needed to maintain the boiling temperature of that liquid. Nobody can take any liquid to a temperature above that liquid's boiling temperature, right? If they could maybe they would find the boiling temperature of a portion of the...
  18. A

    Given a system at pressure p_sat, is the vapor mass fraction unique?

    Assume you have a (closed) system with only one component (for instance water) which is in a pressure-temperature-point (p,T) *on the saturation curve* (i.e. liquid and vapor/gas can coexist). Are the mass fractions in the vapor and liquid phases unique? Or is it possible to change the mass...
  19. M

    Saturation pressure of vapor in air

    If you consider an air - water vapor mixture, total pressure of the mixture consists of water vapor pressure and air pressure. Does saturation pressure of water vapor change if the total pressure (air pressure) is changed. Regards, Mike
  20. H

    Why do bubbles form when vapor pressure = external pressure?

    Can someone explain why bubbles only begin to form when the vapor pressure = external pressure? Since vapor pressure is defined as the equilibrium pressure of the gas in a closed vessel, the connection does not seem obvious.
  21. P

    Enthelpy Change of Ice to Vapor - Show on Graph w/BTU's

    Hi!,If someone could help me. I need to show on a graph (line) the change of state of 1 lb of ice, to water. From -35 degrees F to 50 degrees F showing the BTU's required to do so. And where the latent heat and sensible heat come into the graph. I hope someone understands what I'm saying and can...
  22. R

    Precipitable Water Vapor calculation

    Hi there, I am trying to calculate the precipitable water vapor, or column water vapor amount, from a given volume mixing ratio at a particular pressure. What is the procedure to do this? I understand you can convert volume mixing ratio to mass mixing ratio, by multiplying by the ratio of...
  23. B

    Calculate Mass of Water Vapor in NaHCO3 + HCl Reaction

    Homework Statement Find the mass of water vapor. this is the reaction: NaHCO3+HCl-->NaCl+CO2+H2O V=39.5 L P=18.65 mm Hg T=294 K n=30.5 mol H20 (g) pressure of room= 29.68 inHg=753.87mm Hg Homework Equations The Attempt at a Solution Would i have to use this equation...
  24. G

    Percent water vapor - greenhouse gas

    I'm have armchair interest in greenhouse gases. One of the interesting points is the amount of greenhouse effect that CO2 has versus water vapor. I go to this page http://www.climate4you.com/GreenhouseGasses.htm and find that the relative percentage of atmospheric humidity is 45%. I...
  25. F

    Vapor pressure of water (kinetics)

    Hi All, I tried to collected hydrogen gas generated from the reaction between a metal and hydrochloric acid. I put a inverted conical flask in the water, and the generated H2 would push the water out of the flask, and then the H2 was collected. However, I guess there is water vapor mixed...
  26. T

    What is the Vapor Pressure of a Urea Solution at 24 C?

    Homework Statement If you dissolve 9 g of urea (60.06 g/mol) in 10 mL of water, what is the vapor pressure of the solution at 24 C? Assume the density of water is 1.00 g/mL and the vapor pressure of pure water at 24 C is 22.4 mmHg. Homework Equations Henry's Law, maybe? I'm not sure...
  27. J

    Why Do Deep-Sea Divers Use Helium-Oxygen Mixtures Instead of Compressed Air?

    Air is dissolved in blood and other bodily fluids. As a deep-sea diver descends, the pressure increases and the concentration of dissolved air in the blood increases. If the diver returns to the surface too quickly, gas bubbles out of solution within the body so rapidly that it can cause a...
  28. Simfish

    Using boiling temperature as a proxy for vapor pressure

    So, we know that isopropanol is more volatile than water. We know that since isopropanol has a higher vapor pressure (40 mmHg at 23.8 degrees Celsius, whereas water is 17.5 mmHg at 20 degrees Celsius). We also know that isopropanol has a lower boiling point than water. Now, are there molecules...
  29. R

    [Chemistry] Vapor pressure of water at temperature

    Homework Statement Hi. I'm working on a lab in which I must find the vapor pressure of water. Data that I know is the temperature of the system, the volume of trapped air (2.35 mL), and the atmospheric pressure (1.024 atm). This means that I have 1.1x10^-4 mol of trapped air. Beyond this, I...
  30. R

    [Chemistry] Trying to find the vapor pressure of water with pv=nRT

    Homework Statement A student found that at 750 torr atmospheric pressure and 0.1 deg C, the corrected volume of the trapped air (in a graduated cylinder filled with water inverted in beaker) was 2.20 mL. Under these conditions, how many moles of trapped air are present? This student then...
  31. K

    How to Calculate CaCl2 Concentration from Vapor Pressure Data?

    Homework Statement An aqueous CaCl2 solution has a vapor pressure of 82.3 mmHg at 50 degrees C. The vapor pressure of pure water at this temperature is 92.6 mmHg. What is the concentration of CaCl2 in mass percent? Homework Equations mass %=(mass of component/total mass)*100%...
  32. M

    Vap: Convert Vapor Volume to Density

    Hi Can some one tell me how to convert from vapor volume to vapor density. What i mean is, if a gas have a vapor volume of 0.06883 m3/kg what is its vapor density in Kg/m3 at the same temperature an pressure ?? Marco
  33. M

    Cooling of water vapor - air mixture to T < 273K

    What happens if you cool the mixture of water vapor and air to the temperature lower than 273 K? Since saturation pressure is higher than 0 some vapor should stay in the air. In the solid form?
  34. J

    How do I get water vapor fraction and pressure?

    Hi Guys, I'm building a numerical Matlab simulation of a thermochemical heat storage device (using zeolites), and need to update the state of water vapor in the device at every time step. My question is, if I have an empty space with water in it, with temperature, pressure, density, etc. all...
  35. M

    Vapor Pressure Effects on Material Growth

    hi, I am confused about how the vapor pressure affects the materials growth. Can someone comment on the following : If the vapor pressure of a precursor, let's say N, is high then it will be hard to grow a material containing N because it will be hard to incorporate it onto the substrate...
  36. B

    Sodium Vapor Lamp: Exploring Why We See Only Sodium Spectral Lines

    Hi Why do we have only sodium spectral lines in the sodium vapor lamp despite the very low concentration of sodium present in the lamp.
  37. M

    Simple vapor power plant (thermo I)

    I have a simple vapor power plant with a boiler, turbine, condenser and pump. I have the pressures leaving the boiler, entering the turbine, leaving the turbine and entering the condenser, leaving the condenser and entering the pump. I also have the temps for the above except I have the quality...
  38. A

    Water vapor condensation and freezing

    [b]1. When water vapor is condensing or liquid water is freezing? Homework Equations [b]3. The two are affected by the energy of the sorrounding environment is being absorbed into the water.
  39. E

    Vapor pressure vs liquid pressure in enthelpic combustion reaction

    Homework Statement Hi guys, I'm a little lost on what should probably be a simple question Using the following combustion reaction (C7O2H6)s + 7.5 (O2)g --> 7 (CO2)g + 3 (H2O)l the equation indicates that water produed by the reaction is liquid water not water vapor. Is this correct...
  40. I

    A few questions about steam, water vapor, and humidity

    I'm trying to understand the differences (if there are any) between steam, water vapor, and humidity. First of all, is there any difference between the meanings of the terms steam and water vapor? Is there a difference between the terms "gas" and "vapor" in general? Also, I was under the...
  41. M

    Can air humidity(water vapor) fall like rain in a room?

    Hello, I wanted to know if air humidtiy is high because of a higher temperature does it fall like rain on me or on the clothes or ground what ever after a drop in temperature? The drop in Temperature also means a drop in humidity where does the water vapor goes, i know about cold places...
  42. B

    Physical Chemistry - vapor pressures

    Homework Statement At what temperature will isopropanol (Tbp = 82.5C) and carbon tetrachloride (Tbp = 76.7C) have the same vapour pressure? For isopropanol and carbon tetrachloride, the standard enthalpies of vaporization are 32.54 kJ mol-1 and 44.0 kJ mol-1, respectively. Homework...
  43. F

    Water vapor at approx. 300 degrees Celsius

    Ive heard that at somewhere around 300 degrees Celsius (cant remember the exact number), you can't liquidise it anymore. Is this fact correct? Thanks in advance, fawk3s
  44. R

    Exploring Vapor Pressure: On the Right Track or Not?

    I was thinking about the cause of vapor pressure and thought of how it might work. But I’m not sure if these ideas are on the right track or not. For example water at 373K The fraction of molecules with energy above the heat of vaporization (6.8E-20 J/molecule or about 0.4eV) is about...
  45. W

    Raoult's law - Vapor pressure

    The density of toluene is 0.862g/ml at 25C and it's vapor pressure s 28.44 mmHg. At 25C, the vapor pressure of toluene above a solution of C10H8 in 500ml toluene is 27.92 mmHg. How many grams of C10H8 are present in the solution? I first used Raoult's equation to find X. Then I used the...
  46. B

    What is the mean molecular speed of Mercury Vapor at room temperature?

    I have few questions regarding mercury vapor, except those related to health hazards. What is the mean molecular speed of mercury vapor at room temperature and speed of sound in a pure mercury vapor also at room temperature? Also, for the same density of air at seal level, can mercury...
  47. E

    Saturation of water vapor in the atmosphere

    So I have a quick question about something I'm a bit confused on. I was under the impression that, unlike liquids, gasses become more saturated in COLDER temperatures, rather than warmer. My geology teacher told us that the WARMER it is in the atmosphere the easier it is for water vapor to...
  48. S

    Designing a Vapor Compression & Ground Source Heat Pump System

    please help me ,i have a project which i m not easy with can anyone help me in designing a a vapor compression cycle for cooling in the summer and if desired heating in the winter, and a ground source heat pump for cooling in the summer and if desired heating in the winter.
  49. bearcharge

    COP in vapor compression refrigeration analysis

    Hi, has anybody worked with heat pumps? I'm recently confused about how the heat pump compressor operates. Does it have a fixed pressure or it actually adjust its pressure automatically to outdoor temperature variation? All my confusion originate from the following problem: Now we have a heat...
  50. J

    Standard enthelpy of formation for water vapor

    Homework Statement The standard enthalpy of formation for liquid water is -285.8 kJ / mole. Which of the following could be the standard enthalpy of formation for water vapor? A) -480.7 kJ / mole B) -285.8 kJ C) -241.8 kJ / mole D) +224.5 kJ / mole Homework Equations The...
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