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. G

    Degrees of freedom - molecule of water vapor

    I understand that for H20 in solid form, each atom within the molecule has 6 degrees of freedom; 3 translational and 3 due to potential energy from bonds. Does the number of degrees of freedom change when water changes phase to a vapor?
  2. Averagesupernova

    Mercury Vapor Lights: Safe Indoor Mounting

    Today I was looking around in the local hardware store in the electrical section for some lighting. I have a small building (20 x 30) that I want to light. In the cold months of the year it is not likely it will be heated very warm and florescent lighting is out of the question because of...
  3. S

    Organic Compound's Mass from Vapor Pressure

    Is this even correct? A natural product (MW = 150 g/mol) distills with steam at a boiling temperature of 99 C at atmospheric pressure. The vapor pressure of water at 99 C is 733 mmHg. a. Calculate the weight of the natural product that codistills with each gram of water at 99 C...
  4. P

    Mixture of saturated liquid and saturated vapor

    In the figure that shows saturated vapor and liquid condition under varying temperature and specific volume (constant temperature), there are 2 lines, 1 is saturated liquid line, the other is saturated vapor line. so the region in between these 2 lines is called the mixture of saturated liquid...
  5. E

    A pool with vapor over it at night

    I have a pool that has been above 80 degrees fahrenheit during the night. Recently I went for a swim just after sunset and noticed that I could see what appeared to be steam or some kind of vapor moving over or coming out of my pool. Now I thought it can't be steam, because steam is water in the...
  6. J

    Vapor pressure of Water calculation

    Ok, I need to calculate the vapor pressure of water. All the information I am given is that the temp is 43.0 C, and I know the total pressure of the system is 758.3 torr. Is there anyway I can calculate this using the Pwater = Ptotal - Pair equation? There is also another equation that...
  7. S

    Exploring Vapor Pressure: Ice at 0°C in a Vacuum

    Can anyone help to explain what vapor pressure does...i know what it is...but how can it be used if you put a cube of ice at 0 degrees C, in a vacumed container (amospheric pressue equals zero) won't the ice all go to gas, since its vapor pressure is greater than the atmospheric pressure...
  8. A

    What is the Van't Hoff factor for NaCl in seawater?

    X_1=\frac{n_1}{n_1+n_2}\implies n_2=\frac{n_1-X_1n_1}{X_1} where n1 is the moles of solvent and n2 is the moles of solute. 22.98=X_1\left(23.76\right)\implies X_1=.9672 and 1000 g of water is equal to 55.49 mol (n1), so plugging this all in gives: n_2=1.88\text{mol} which would be...
  9. A

    Calculating Vapor Pressure Lowering for Glucose-Water Solution at 25oC

    I calculated that there is 41/90 mol glucose and 92/3 mol water. Then I calculated the molar fraction of solvent in the solution, which I found to be .985. Next I multiplied the .985 by 23.76 mmHg and came up with 23.4 mmHg. To find the "lowering," I subtracted this from 23.76 coming up with...
  10. F

    Sodium vapor lamps - how do they work

    I don't quite understand the explanation at wiki; What does this mean (the vaporizes bit)? the sodium turns to gas, which then glows? when it cools does it condense back to a solid when its turned off again?
  11. W

    When hydrogen and oxygen gas combine to form water vapor

    Just took a chemistry test, had a few I wasn't sure of: When hydrogen and oxygen gas combine to form water vapor, what mass of water forms if 10grams of oxygen reacts completely? 2H_2 + O_2 \rightarrow 2H_2O 10 grams of oxygen is .625 moles, and the stoichiometric ratio is 1:2, so...
  12. N

    Superheated vapor tables for propane

    Hi, I was wondering if anyone knew a site where I could find the superheated vapor tables for propane. It's not in my thermodynamics book and I spent some time searching online and couldn't find it there either. I really need it to find the specific volume (ft^3/lbm) for T = 80 F and P = 125...
  13. P

    Oentane is a liquid with a vapor pressure of 512 Torr at 25C

    Oentane is a liquid with a vapor pressure of 512 Torr at 25C; at the same temperature, the vapor pressure of hexane is only 151 Torr. what composition must the liquid phase have if the gas hase composition is to have equal amounts of pentane and hexane? Do I use p = i M R T to solve for the...
  14. C

    Calculating Vapour Pressure for 1L Container with 5mL Water at 20°C

    a 1 L container with 5 mL of water held at 20degcel I have to figure out the vapour pressure. I was told to use PV=nRT..but how do I find n? thanks
  15. I

    Vapor Density: 1.3 - What Does it Mean?

    For a solution It says; VAPOR DENSITY: 1.3 Is VAPOR DENSITY the same as Density of that solution? And what is the unit of 1.3? Hope for inputs. Thanks
  16. P

    Vapor Pressure in fresh vs salt water

    For water at 30°C, when 100 g of pure water the vapor pressure is 31.82 mm Hg and when 50g of NaCl dissolved in 100g of water vapor pressure is 27.68 mm Hg The vapor pressure of pure water is different than the vapor pressure of water in a salt water solution. Explain why. Can anyone...
  17. F

    How to Calculate the Mole Fraction in a Pentane-Hexane Solution?

    Hi I have difficulties with a problem that my teacher gave in assignement. Teh teacher said it was a bit higher than our level but I think it far above what I am able to do! so here it is : The vapor pressure in equilibrium with pentane-hexane solution at 25°C has a mole fraction of...
  18. P

    Carbon Vapor and Gaseous Carbon

    Is it possible to maintain pure carbon gas at room temperature? Suppose I start with a vacuum chamber and allow a small amount of hot, gaseous carbon vapor inside it, but only enough so that it remains gaseous at normal room temperatures - is that possible to do? Where can I find formulas to let...
  19. M

    Concentration of water vapor present at equilibrium

    3 Fe (S) + 4 H2O (g) = Fe3O4 + 4 H2 (g) This equilibrium has a Kc of 4.6 @ 850 degree C. Determine the concentration of water vapor present at equilibrium if the reaction is initiated using 8.00 grams H2 and an excess of iron oxide, fe3O4, in a 16.0 liter container. This is what I...
  20. L

    Better fuel efficiency through vapor carburators?

    I'm sure everybody has heard all the stories about high mileage carburators and the oil companies etc. But why has this problem not been solved? Approximately two thirds of the fuel we burn in our cars goes out the tail pipe. I've read that someone has used catalytic cracking to breakdown the...
  21. I

    How Do You Calculate the Mole Fraction of NaCl in a Solution?

    Here is the question: A solution of sodium chloride in water has a vapor pressure of 19.6 torr at 25 degrees celsius. What is the mole fraction of NaCl in this solution? The vapor pressure of pure water is 23.8 torr at 25 degrees celsius...
  22. Greg Bernhardt

    What is the heat of formation of water vapor?

    At standard temperature and pressure, what is the heat of formation of water vapor?
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