Questions tagged [vapor-pressure]

This is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. Apply this tag to questions involving clarification related to vapor pressure.

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Quantitative Transfer of Volatile Standards

(Edited w/ updates) Okay, long story short I work in a lab which has been working on cannabinoid analysis (in the licensed Canadian market) and have had a lot of issues surrounding the standards/...
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711 views

Vapor-pressure or Vapor-concentration

To summarize from my textbook: rate of evaporation: proportional to surface area but essentially independent from pressure (of surrounding gas) rate of condensation proportional to both surface ...
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53 views

Can a droplet of formalin evaporate in midair while falling?

I am designing an evaporator for use in an enclosed environment. Due to the hazardous nature of formaldehyde, I want my evaporator to be wick-free. The environment in which the evaporator will be used ...
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729 views

What is the relation between pressure and chemical potential?

I know that in a two-component gas-liquid system (for simplicity) the chemical potential $\mu_i$ ($i=1,2$) and total pressure $p$ can be defined by $$\mu_i=\left(\frac{\partial U}{\partial N_i}\right)...
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47 views

Can different components show different deviations from Raoult's law?

Introduction: Raoult's law is used to calculate the partial pressures of the vapour phases of volatile components of a solution Given that there are two components, A and B, in the liquid-liquid ...
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35 views

Why does refrigerant condense in oil?

In a closed system (think of a typical AC system) why does refrigerant tend to condense and settle in oil? I’ve heard that the vapor pressure of the oil is very low so that causes a pressure ...
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26 views

Working out energies of hydrogen bonds by comparing chemical potential of vapour and condensed phase - equation derivation

I want to ask a question about working out the energy of a hydrogen bond between two water molecules, $w_{AA}$ using the chemical potentials of vapour and condensed phases. I was reading K. Dill, ...
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93 views

Measuring vapour pressure in a closed system

My experiment requires the determination of vapour pressure from which I will calculate the number density (or number of moles of the molecule) later, for a closed system. Here's my setup : Liquid ...
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173 views

Why does only a single azeotropic composition exist for a mixture of two given substances?

In the image below, which represents a generic composition vs. temperature plot for a mixture, there is a single intersection point between the vapor and liquid curves. This is due to the fact that ...
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212 views

Alternative to mercury bubbler for increasing boiling temp?

A common reaction for forming the octachlorodirhenate(III) anion is to heat tert-n-butylammonium perrhenate in benzoyl chloride at 209 ºC. If you look up the info for benzoyl chloride, one sees that ...
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90 views

Chemically generating a high vacuum?

Suppose I fill a vacuum chamber with 99% oxygen, then pull a vacuum on it down to 10 pascal absolute. If I then vaporize aluminum (for vapor deposition), will the aluminum bind with the remaining ...
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540 views

Why does cooking oil lower the vapor pressure of water?

I added different amounts of oil to different containers with 50mL of water and weighted the containers. Then I heated the containers for 15 minutes in a water bath and weighted again. I noticed that ...
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Unable to comprehend graph of aqueous lithium bromide vapour pressure

$\ce{LiBr}$ $Vp$ chart: http://www.mediafire.com/view/x77zc8wj11gthsj/LiBr_Vp.jpg or http://www.mediafire.com/view/u4dnocvbsf3atmu/Useful_Chart_LiBr.pdf Lecture in question (p.13) http://www....
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961 views

How are pressure vessels heated?

I'm working on a project in which I'll be dealing with pressure vessels. As of now I've drawn/conceptualized everything on theory basis. The diagrams are made on the basis of theory, but then I came ...
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1answer
131 views

Is every substance in equilibrium with its vapours?

In one of my previous questions, I got an answer from user Jan: The smell of a compound as we perceive it usually depends on which receptors in the nose will bind the molecule (or not). These ...
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Saturated vapor and liquid densities (VLC curve) from Helmholtz free energy equation of state

I have been reading about the statistical associating fluid theory (SAFT) which computes the Helmholtz free energy ($A$) from the SAFT EoS (a hell lot of equations) for a molecule of interest, and is ...
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36 views

Conditions for a substance to show deliquescent or efflorescent behaviour

I have learnt that deliquescent substances are the ones which absorb moisture from the surroundings and convert them to solution and efflorescent substances are the ones which release moisture into ...
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36 views

Does aqueous ammonium fluoride solution release hydrogen fluoride vapors?

Can $\ce{HF}$ vapors be released from $\ce{NH4F}$ solution in water $(w(\ce{NH4F}) = 40\,\%)$ at room temperature? I assume that dissolving $\ce{NH4F}$ in water produces small amount of $\ce{HF}.$
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104 views

Phase rule for a pure substance in vapor-liquid region

I'm confused with how the Gibbs Phase Rule works for pure substances in liquid-vapor mixtures. According to the phase rule, there should only be one degree of freedom for a two-phase mixture with a ...
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20 views

Algae Cultivation Using Polyethylene Film Reactor Vessel Floating In Pool with Algicidal ClO2 Concentration

I'm attempting to grow chlorella algae in a polyethylene film bag (which contains the growth medium) submerged in a temperature-moderating, above-ground swimming pool. This presents a challenge in ...
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184 views

How to find relative lowering of vapour pressure from phase diagrams in terms of temperature?

Problem Answer My question Does a tie rule exist for solution solvent phase diagram to express relative lowering of vapour pressure in terms of temperature? The phase diagram is the one ...
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50 views

Issue with evaporation rate of water

The evaporation rate of water (kg/s) is given by: $$g = \frac{P}{P_o} AΘ$$ Where $P$ is given in Pascals and $A$ is the surface area (in $m^2$) and $Θ$ is the empirical evaporation coefficient: $$Θ = ...
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Volume of dried gas at STP

A $54.0\ \mathrm{mL}$ sample of oxygen is collected over water at $20\ \mathrm{^\circ C}$ and $770\ \mathrm{Torr}$ pressure. What is the volume of the dry gas at STP? By using the combined gas law, I ...
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55 views

How does association within vapor or dissociation within liquid affect the ideal nature of a binary solution?

As I understand, when there is positive deviation of a binary solution from Raoult's Law, the equilibrium partial pressure curve approach ideality (i.e a straight line dependence of equilibrium ...
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91 views

What causes both components of a binary gas mix to condensate at the same time for a given composition

Okay, so recently I encountered the temperature - mole fraction diagrams for binary vapour-liquid equilibrium. For now, I only consider two-component systems where the components are very similar and ...
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188 views

Anhydrous ammonia vapor-liquid equilibrium

I have been given a anhydrous ammonia vapor liquid system in an air-tight container where the pressure is 30 bar and the temperature is 30 degrees. They claim the system is in equilibrium, which I ...
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974 views

Predicting the vapor pressure of water ammonia solution

I am working on a project that involves the compressors for a vapor compression refrigeration cycle of R717 (ammonia) and came across something that has been boggling my mind a little bit for no good ...
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803 views

Rate of evaporation of mercury

A restorer of antique barometers reported in a blog post that he has had a barometer on his wall that has shown no "visible" loss of mercury in 15 years. I was kind of curious about this, wondering ...
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457 views

Identifying T1 and T2 in the Claperyon equation

Is there a way to identify T1 and T2 in the two point form of the claperyon equation? I suspect that the greater temperature is T1 and the smaller temperature is T2.
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135 views

how to find pressure of a liquid when given volume (1 and 2) and one pressure?

A 5 mL sample of an unknown liquid is placed into a 250 mL flask that has had all of the air removed. The pressure measured in the flask is found to be 35.4kPa. In a seperate trial the student puts ...
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2k views

Why does melting point depend on external pressure?

The melting point of a substance is the temperature at which the solid form's vapor pressure equals the liquid form's vapor pressure. I read that the vapor pressure of something depends ONLY on the ...
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1answer
183 views

Applying Raoult's Law in volatile solids–liquid solutions

My textbook explains applying Raoult's Law for the two cases: liquid–liquid solutions, in which the vapour pressure of the solution is due to both the components non-volatile solids–liquid solutions, ...
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Interpretation of azeotropes from statistical mechanics derivation

In an earlier posted question titled Reason for the formation of azeotropes, @porphyrin presented an elegant derivation from statistical mechanics to interpret partial pressures for the two components ...
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1answer
65 views

Does the vapor pressure of a substance depend on the presence of other gases?

The Clausius-Clapeyron equation (CC equation) can be used to find the (saturated) vapor pressure of a substance ie. the gas pressure at which the two phases (vapor + liquid or vapor + solid) reach ...
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50 views

How to sustain iodine vapor in a big container (V=200 L)?

I am lost in a quest on how to have a big container in which I can have iodine vapor at a known temperature. We intend send iodine into an air flow, and observe fluorescence of iodine in this flow. ...
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94 views

Relation between vapour pressure and boiling point

In my childhood I was very happy with the following definition of boiling point The temperature at which a substance changes from liquid phase to gaseous phase is known as boiling point. But with ...
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20 views

Is saturated vapor pressure equals to saturated vapor partial pressure?

I got confused for this two things, the first pressure is the pure water vapor in a certain temperture, and the second vapor partial pressure is the water vapor existed along with other gases, so my ...
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87 views

Why is vapor pressure constant at boiling point?

At non-boiling point, I understand that when you add heat, temperature increases and also the amount of gas increases, so by using $PV=nRT$ at constant volume, the increase in $n$ and $T$ would ...
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35 views

The minima of minimum boiling azeotropes

This is a very basic doubt, so I'll be really brief about it. The discussion I raise is particularly about minimum boiling azeotropes but it's understood that whatever I ask is about the general ...
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35 views

Is the evaporation (liquid to gas conversion) of ethanol dependent on how full you fill it up in a sealed bottle?

It seems intuitive to think that in a bottle (which is air-tight), if you fill up ethanol (or any other volatile liquid) to very full extent, thereby leaving very little headspace, the amount of ...
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29 views

Combining two high-VP chemicals to get a low-VP mixture

I'd like to do a class experiment as a metaphor for human relationships. Two people each have a different chemical which evaporates quickly (at STP). There is one glass between them. If only one ...
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103 views

Will evaporation from two immiscible liquids blow up a balloon?

Consider the following setup: Two immiscible liquids A and B are placed inside a balloon at a temperature where neither one of them boils. The inside of the balloon contains some argon, and the ...
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124 views

For azeotropic mixtures, is the total vapour pressure at equilibrium equal to the partial pressure of one of the components?

I know, a ridiculous statement. But here's how I reached at it . Say we have a solution of two components liquids A and B. By Raoults law, $$p_A= p_A^o \times x_A \tag1$$ Also by Dalton's law, $$...
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683 views

Water vapor equilibrium calculations

The question had two parts. The first part said: Calculate the amount of water required to saturate a vessel of volume 82 L at 300 K given that the vapor pressure of water is 38 torr at 300 K. The ...
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130 views

vapour pressure above 2 separate beakers containing liquids which form ideal solution

Suppose we have A moles of liquid 1 in one beaker and B moles of liquid 2 in the other. Beakers are placed together in a biger closed container. Both have different vapour pressure when isloated. Now ...
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920 views

Why is the temperature graph sigmoidal in simple distillation of components with very different bps?

I'm writing an organic chemistry lab report on distillation and I thought I understood this, but the more I look at my lab textbook, I realize I don't. My textbook 1 explains that the temperature of ...
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What is the ∆H_vap when temperature of a given liquid is equal to the boiling point of the liquid?

What is the $∆H_{vap}$ when temperature of a given liquid is equal to the boiling point of the liquid? For the other cases ie (i) T>BP, $∆H_{vap}$ > 0 (ii) T<BP, $∆H_{vap}$ < 0 So what ...
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1k views

How can I calculate the concentration of ethanol vapor in an airstream?

How can I calculate the concentration of ethanol vapor in an airstream? The steady state generation flow rate (of the vapor) is 625 ft^3/min. The ambient temp is 50-60 F (we can use avg temp 55 F). ...
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1answer
151 views

Can a solid have a vapor pressure without the ability to sublimate?

Does sublimation occur when a solid turns into a gas and THEN vapor pressure is produced or does the solid first have a vapor pressue and then when the vapor pressure of the solid equals the ...