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. tbn032

    Problem regarding vapour density of a mixture

    The vapour density of N204 at certain temperature is 30. Calculate the percentage of dissociation of N204 at this temperature. N2O4(g)⇌2NO2(g)? I am unable to understand the concept behind vapour density of the mixture. Currently, I understand that 2 x vapour density=molar mass. Vapour density =...
  2. S

    I Vapour pressure/solubility of small and big grain surfaces and corners

    When a condensed phase - solid or liquid - is in an immiscible fluid (gas or liquid), it has surface energy. Several small pieces of condensed phase have bigger combined surface than one bigger piece of the phase of the same volume, and thus bigger energy. In case of liquid, the surface of a...
  3. B

    Vapour Absorption Cycle Questions

    Hi all, I'm doing some research on vapour absorption cycle machines, mainly water ammonia refrigerators. I've got a few questions. 1. What is the role of the water absorber? ie why do we need the water? 2. In the absorber we have a water ammonia solution. Is the ammonia a gas in the solution...
  4. B

    Saturated vapour pressure vapour quality and T-S diagram location

    Hi all., Just hoping to get a better fundamental insight into a few things. If we start with this: http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/vappre.html so we have a closed container at a given temperature, then we can find it's saturation pressure. All good so far. In the following...
  5. D

    Chemistry What is the Correct Formula for Calculating Vapour Pressure of Solutions?

    Isn't the formula to be applied ##P= \chi_{solvent}P^o _{solvent}##? in which ##P^o _{solvent}##= 18.7mmHg and ##\chi_{solvent}= \frac{mol_{solvent}}{mol_{solvent}+mol_{solute}}=\frac{9.0 mol}{9.0 mol+0,50 mol}## but seems doesn't leads to the expected result
  6. I

    5G and future 6G terahertz absorbed by water vapour = heating?

    I just found this piece in an article: Terahertz waves (THz), which are submillimeter waves sitting between microwave and infrared light on the electromagnetic spectrum, have been used to achieve data rates greater than 100 Gbps. Unfortunately, THz waves share an Achilles’ Heel with the...
  7. J

    Understanding Vapour Pressure & Temperature Difference

    I have a problem at the very beginning. I don't know how to relate this vapour pressure to the temperature difference. I have read the hint: Recall the idea 7: for dynamical processes, at first, a mechanical equilibrium is reached, which means the equality of pressures; the other equilibria...
  8. A

    Vapour pressure of water vapour in air

    Vapour pressure in a closed system. Why does the partial pressure of water vapour in air equals to the equilibrium vapour pressure of liquid?
  9. W

    Disappearance of vapour trails - more warming?

    I think it was back around the 9-11 events that South African researchers happened to notice that solar radiation received at ground level increased by around 10% during the grounding of airline fleets world wide. If I remember correctly, this led to a measurable increase in plant growth over...
  10. okandrea

    Engineering How do I calculate the overall vapour flow?

    Step 1: Values are from textbook 'Building for a Cold Climate' Mbrick = 46 ng/s*Pa*m^2 Mgypsum = 2870 ng/s*Pa*m^2 (for 9.5mm) took the above value and used ratios to determine permeance for 10mm Gypsum board (2870/9.5 = X/10) Mgypsum (new value) = 3021.05 ng/s*Pa*m^2 Step 2...
  11. M

    Thermodynamics - water vapour cycle

    Homework Statement How to calculate the specific work done. Homework Equations Water vapor initially at 10 bar and 400 °C is contained within a piston-cylinder assembly. The water is cooled at constant volume until its temperature is 150 °C. The water is then condensed isothermally to saturated...
  12. Death eater

    When boiling water, what is the degree of freedom inside the vapour dome?

    When water converts to steam while boiling a vapour dome can be formed, what is the degree of freedom inside this vapour dome and on the saturated points?
  13. navneet9431

    Calculating Percentage of Dissociated N2O4 Molecules: Vapour Density Question

    Homework Statement The vapour density of a sample of N2O4 gas is 35. What per cent of N2O4 molecules are dissociated inNO2? Homework Equations molar mass = 2 * Vapour Density The Attempt at a Solution I tried to solve this question this way, Let the initial number of moles of N2O4=a and...
  14. S

    I Solid diprotium saturated vapour density

    What precisely is the equilibrium vapour density of bulk solid diprotium surface now, at 2,7 K? The density of the world falls with some power of temperature (which one?). The density of saturated vapour falls exponentially. At which temperature shall the world saturate with respect to bulk...
  15. R

    Does water vapour absorbtion depend on H2O conc or RH?

    Hello If I blow air containing a fixed kg/m3 of water vapour over anhydrous CaCl2, will the absorbtion rate change if the air temp is different? To simplify, we neglect exotheric heat generated by hygroscopy. Thanks for your answers to this rather simple question.
  16. W

    Partial Pressures and Vapour Pressure

    Homework Statement Two systems in diffusive equilibrium have equal chemical potentials. We can use this fact to solve the following problem. We begin with a closed system consisting of a liquid such as water in diffusive equilibrium with its vapour. At the start, only the liquid and its vapour...
  17. EEristavi

    I Liquid boiling and Evaporation

    In the normal conditions (sea level) water evaporates at 100 C. In thermodynamics, we say: the amount of energy Q, can raise temperature of the liquid by the formula Q1=cm(t2-t1); when the liquid reaches the boiling point (100 C), we write Q2=Lm. Q2 is entirely spent on changing liquid state...
  18. R

    How to calculate percentage of water vapour that condenses?

    Homework Statement 1kg of moist air of RH 70% at 21oC is cooled at a constant pressure of 1 bar to 5oC. The vapour pressure at 21oC and 5oC are 0.025 bar and 0.0087 bar. The percentage of water vapour that condenses into water at 5oC is? Want to check whether my intuition & logic are correct...
  19. Wrichik Basu

    B Obtaining spectrum of Sodium from Sodium Vapour Lamp

    I learned that two lines in the emission spectrum of Sodium, namely ## D_1 ## and ## D_2 ##, are on the visible region of the spectrum. Can I obtain these lines from a Sodium vapour lamp? I want to use a prism to separate out the individual wavelengths, a no then use a photographic film to...
  20. Strawberry1711

    Liquid and vapour in equilibrium

    Homework Statement A liquid is in equilibrium with its vapour at it’s boiling point. On the average, the molecules in the two phases have equal;; provided options are: a. inter-molecule forces b.potential energy c .Kinetic energy d.total energy . Homework EquationsThe Attempt at a Solution ...
  21. Ravi Singh choudhary

    Gibbs phase rule use for wet vapour

    I have a doubt regarding gibbs phase rule in thermodynamics.. It says the number of independent intensive properties required to specify the state of a system is F=C-P+2 where C is number of components and P is the number of phase.. So for a water and water vapour system, C=1, P=2 . So F=1. If...
  22. Ravi Singh choudhary

    Vapour pressure vs saturation pressure; too much confusion

    It was only the psychrometry came; I read about vapour pressure is equal to the saturation pressure at 100% relative humidity. While before even in the textbooks both terms are used frequently as same. I fully understood what saturation pressure is; learned during phase change phenomenon of...
  23. S

    Automotive Vapour absorption cooling system for cars

    Is to possible to provide cooling for automobiles using vapor absorption compression system utilizing the exhaust gases? If possible how efficient can this method work?
  24. avito009

    Why Does More Vapour Form When Taking a Bath in Colder Weather?

    When the temperature in a city is lower and one has a bath in the bathroom then why does more vapour get created? More vapour than it would be created when the temperature is higher?
  25. lamejane

    E-beam Physical Vapour deposition

    Hope we have some PVD specialists in the house :) we have a pfeiffer e-beam PVD in the lab which i use to deposit Ni and Pt thin films ( around 100nm each) on Si wafers. I have always had the problem of "Ni splashes" while heating the target ( with the e beam) which leads to a process stop (...
  26. C

    How Does Vapour Pressure Change at Dew Point for Benzene-Toluene Mixtures?

    THERE IS NO TEMPLATE BECAUSE GHIS HOMEWORK WAS PLACED IN AN INCORRECT FORUM Equimolar benzene and and toluene form essentially ideal solutions. At 20degC the vapour of benzene and toluene are 9.866kPa and 2.933kPa respectively. The solution is boiled by reducing the external pressure below the...
  27. jmarkwalker

    Evaporating water using heat and reducing vapour pressure

    I want to reduce the amount of water present in the digestate coming out of my Anaerobic Digester. The traditional method would be to boil it until I've removed as much off as I want. However, this is expensive from an energy consumption point of view. There's a great video on Youtube showing a...
  28. A

    Estimating Vapor Pressure of Mercury at 25°C Using Appendix D Data

    Homework Statement Estimate the vapor pressure of mercury at 25 ∘C (use data from Appendix D from the textbook). Homework Equations Using the appendix I can find ΔG, ΔH, and ΔS. The Attempt at a Solution I have no idea where to start. I think that maybe vapor pressure would be found when...
  29. I

    Confused on a question about vapour refrigeration cycle

    Homework Statement http://photouploads.com/images/ae1d2f.png Homework Equations N/A The Attempt at a Solution In the image linked above, I have copied and pasted 4 different slides. In the last slide, I am confused how they got the expression for T2 (the working out). I know that they did...
  30. I

    Ph diagram for a vapour compression cycle

    Homework Statement Homework Equations N/A The Attempt at a Solution I am trying to understand the above ph diagram (for a vapour compression cycle), In some examples, point 1 is situated as above in the image (i.e. to the right of the saturated vapour line) and at other times it's situated...
  31. Janson Raymond Kenny

    Acetic Acid + Ammonium Hydroxide Vapours

    Hi! I work in the movie business doing Special Effects. To create smoke for some effects we use "A+B Smoke." It is simply a mix of Acetic Acid (Part A) and Ammonium Hydroxide (Part B). However, the smoke effects is created when the VAPOURS of these 2 chemicals mix in the air. The MSDS Safety...
  32. L

    Why are vapour cones from aircraft cones?

    Does the vapour cone from a high-speed aircraft correspond to the Mach angle of its sonic boom? What is the general physics responsible for a vapour cone, and why does it resemble the shape of a cone? Basically I'm wondering if this : corresponds to this :
  33. L

    Determining boiling point from vapour pressure

    Homework Statement When benzene freezes at 5.5 C its density changes from 0.879 g cm-3 to 0.891 g cm-3. Its enthalpy of fusion is 10.59 kJ mol -1. Estimate freezing point of benzene at 1000 atm Homework Equations Solid liquid boundary: p=p*+ΔHfus/ΔV ln(T/T*) The Attempt at a Solution From the...
  34. P

    Saturation vapour pressure equation formula

    Pws=1000⋅e[[52.58]-[6790.5/T]-[5.028lnT]] T= temprerature in Kelvin Pws= Saturation vapour pressure I plugged in my temperature to the formula in Kelvin, I couldn't arrive at the correct answer. How do you get the e value of the equation (superscript above). My problem could be the trigonometry...
  35. Eclair_de_XII

    Am I doing this vapour pressure problem correctly?

    Homework Statement 'The vapour pressure of ethanol (C2H5OH) at 19°C is 40.0 torr. A 1.00-g sample of ethanol is placed in a 2.00 L container at 19°C. If the container is closed and the ethanol is allowed to reach equilibrium with its vapour, how many grams of liquid ethanol remain?' Homework...
  36. G

    What is the relationship between partial pressure of vapor and vapor pressure?

    1) We know that when both liquid and vapor are present, and system of these is in phase equilibrium; the "partial pressure of the vapor" must be equal to the "vapor pressure" , i.e. : partial pressure of vapor= vapor pressure. 2) However, what happens if there is no liquid in the system, i.e...
  37. daPope

    Have mass flow rate, want superficial vapour velocity

    Hi guys, quick simple question. Lets say I have a pipe separated into 3 sectoins (all horizontal), all have the same flow areas. In the first section it is all liquid water. I know the mass flow rate in this. In the second section the water is heated. And I can work out the steam quality...
  38. A

    Boiling point and vapour pressure

    Hi all, I am facing difficulty in understanding the reason behind the fact that a liquid boils when the atmospheric pressure is equal to its vapour pressure. We know that at the vapour pressure, the air and the liquid remain in equilibrium, so there's no net evaporation or condensation. So...
  39. S

    Non-ideal solution and vapour pressure

    When there is a positive or negative deviation it is due to the interactions between A-A and B-B being weaker or stronger than the interactions between A-B. However, are there any scenarios where the interactions between A-A are stronger than A-B while B-B weaker than A-A or vice versa? In such...
  40. A

    Finding vapour pressure using compressibility chart

    Homework Statement I was asked to find the vapour pressure and saturated liquid molar density of propane at 263.15K using a generalised compressibility chart. (not allowed to use NIST or steam tables either, the chart i was given does not have reduced volume lines) Homework Equations Tr=T/Tc...
  41. U

    Is an asthma inhaler (MDI) an example of vaporization?

    I am trying to give some context to medical vaporizers in a literature review I am composing and initially decided to give asthma inhalers and nasal inhalers as examples. I realized however, that some sources on-line were referring to these metered dose inhalers as vaporization devices when...
  42. G

    Saturated vapour pressure - why an equilibrum is reached?

    Hello, I've read about the concept of saturated vapour pressure on some sites but none of them really explain why the equilibrum happens and that's what I want to ask you. Why the number of particles leaving the surface and joining the surface can't change over time and never reach the equilibrum?
  43. R

    Design of Vapour Compression Refrigeration Cycle

    Hi! For our class project, we have to design a system that freezes an amount of water as quick as possible. The refrigerant is R134a. The compressor is known. I don't really know how to get started here. How do I choose the evaporator pressure and the superheating, and equally the condensor...
  44. U

    Liquid, superheated vapour and a mixture

    Homework Statement how do i determine whether water is at liquid, superheated vapour r a mixture state?? Homework Equations The Attempt at a Solution
  45. M

    Relationship of vapour pressure and Dew Point

    Homework Statement Moist air at 32 degrees C has a dew point of 26 degrees C. The total or atmospheric pressure is 100.7kPa. find the: Molal Humidity Relative Humidity Homework Equations Molal Humidity = \frac{P_{i}}{P_{tot} - P_{i}} Relative Humidity = \frac{P_{i}}{P_{vap}}...
  46. M

    Substance is in equilibrium between its vapour and liquid

    In Chemistry, if a substance is in equilibrium between its vapour and liquid, does it account for the dissolved gas molecules? I have always heard that the rate of evaporate = rate of condensation in a case like this, but does the rate of evaporation include the dissolved gases escaping and...
  47. M

    Vapour Pressure: Exploring How Molecules Escape Into Gas Phase

    I read in my Chemistry workbook that: "At higher temperatures, vapour pressure increases as more energy is provided to the liquid molecules, allowing them to escape into the gas phase." At the boiling point, all energy is gone into breaking bonds and to convert liquid phase molecules into...
  48. P

    Condensing Vapour at 52 Degrees - 2500kg/hr

    I have read the rules and this IS not homework...i work in a factory Hi I have Vapour at 52 degrees from a tank (-87.7kPa) going to a Condensor (heat exchange) under vacuum pressure (-87.7kPa)...The Condensor uses water on 1 side to condense vapour on the other side... 1. What...
  49. T

    Specific Heat of Liquid Saturation Line and Vapour Saturation Line in RefProp

    Hello There, So I made a plot of some specific heats in refprop, and I chose the "Draw Saturation Lines" option. When I did this, the follow chart was produced. http://i.imgur.com/h34Pq.png Now my question is, what are these saturation lines representing? -TP
  50. J

    Vapour Pressure: Pressure Exerted on Liquid & Container

    According to Wikipedia, vapour pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. Does that mean the pressure the vapour exerts on the container or the pressure the vapour exerts on the liquid?