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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Mathematical models of Vaporization-Condensation dynamics

I am a mathematician now studying an introductory chemistry course. Consider a liquid in a closed container, at (say) room temperature. Then some of the liquid will vaporize. Then some of the ...
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Water Vapor Permeable Membranes

Could someone recommend a vapor-permeable membrane that allows passage of water vapor and air but not liquid water or any other solution? I am trying to maintain the relative humidity of a thermally ...
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Vapor-Liquid Equilibrium and partial pressure of ammonia

I tried searching the forums for a similar question but I do not think it was entirely answered: Suppose I have a closed system in a container with solvent and a certain concentration of gas, say ...
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How do water vapor molecules push other air molecules away?

I've read that when water vapor enters the atmosphere, the vapor molecules push the oxygen and nitrogen molecules out of the way and occupy their space. But if water vapor molecules are lighter than ...
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Can vapor pressure be defined for permanent gases?

Vapor pressure of a substance, in a given temperature, is the pressure exerted the vapor in a system where the gaseous and liquid phases of the pure substance are in equilibrium. But, if for a ...
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How do you derive the boiling point elevation equation using Raoult’s law and Clausius-Clapeyron relation?

I know that Raoult's law is $P_{solution}=X_{solvent}P_{solvent}$ and Clausius-Clapeyron equation is $ln(\frac{P_{2}}{P_{1}})=-\frac{L}{R}(\frac{1}{T_{2}}-\frac{1}{T_{1}})$ But how do you derive the ...
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Saturation of air within isolated system with water and ethanol

I am planning an experiment in an isolated system that contains two droplets. One droplet is water and the other one is a 40% ethanol-water mixture. The isolated compartment is filled with air at 20°C....
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Vapor pressure in closed systems (2 and multiple components)

Hi there I am currently struggling to understand how vapor/liquid systems work in general. Specifically, I have two qualitative questions. Suppose we had a closed system, half of it filled with just ...
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Why does Raoult's Law have a weighted sum instead of a direct sum?

I'm fully aware of the various questions asked about Raoult's Law, and I'm asking this after having gone through all of them and not finding a suitable answer to my question. I have studied, that at a ...
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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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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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Do benzene and hexane form an ideal solution?

My teacher said that benzene and hexane do not form an ideal solution (with reference to Raoult's law) but did not explain any reason for it. My approach: Cyclic hydrocarbons (benzene here) have ...
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Pressure increase in a chamber with 1 ml of water heated to 200 °C [closed]

For safety reasons I want to know how much pressure will be generated in a sealed chamber with $1~\mathrm{ml}$ of water, pure nitrogen at $1.3~\mathrm{bar}$ at $22~\mathrm{^\circ C}$. This chamber ...
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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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Is there a vapor pressure equivalent to freezing point?

Vapor pressure is where liquids are breaking off into the gas phase, below the boiling point. So is there a term where solids break off into the liquid phase, below the freezing point? Vapor pressure ...
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Data on Vapour Pressures of Silicone Oils [closed]

I am trying to find specific information on vapour pressure of silicone oils with different viscosities which I have used in some experimental work. Is there a chemical databook where this information ...
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Vapour pressure and boiling [duplicate]

I have come across two definitions for boiling point: It is the temperature at which a liquid gets vaporised It is the point where vapour pressure = external pressure How are they related? How does ...
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Why does boiling occur when vapor pressure equals ambient pressure?

Here is my understanding of the boiling process: pressure of the atmosphere is pressing down on the liquid and this pressure is propagated throughout the liquid. That is, pressure everywhere inside ...
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1 answer
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Some salts lower the vapour pressure of water - do any raise it?

Plain old NaCl salt can slightly lower the vapour pressure of water for a given temperature. Other salts such as CaCl₂ lower the vapour pressure to a larger degree. Do any salts, or compounds of any ...
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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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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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Variation of vapour pressure with application of external pressure

Many times study of fact that with pressure of a substance only depends on the temperature and nature of the substance recently I study about dew point and bubble point. Then I came up with this ...
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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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1 answer
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In an open system, can water vapor escape into the atmosphere before reaching the boiling point? [duplicate]

In a closed system, water vapor would have nowhere to go and atmospheric pressure would not be a factor. It would reach dynamic equilibrium with only water vapor. But in an open system, I think that ...
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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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Why vapor pressure is unaffected by change in atmospheric pressure [duplicate]

I am a high school student and I am very confused in a topic about "vapor pressure of liquid". Why doesn't a change in atmospheric pressure affect vapor pressure? I think intuitively that ...
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1 answer
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What does water saturated oxygen mean? [closed]

What does water saturated oxygen mean in this question: The vapour pressure of water at 80º C is 355 torr. A 100 ml vessel contained water saturated oxygen at 80º C, the total gas pressure being 760 ...
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Does pH gets affected by pressure? [closed]

My attempt- I thought that pH is h+ ion concentration and change in volume will change its equilibrium according to le chatelier's principle . But I want to know is it correct or it needs some ...
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1 vote
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Which temperature would allow a molecule to vaporize at ultra-low pressure? [closed]

I must vaporize a molecule with a normal boiling point of 320°C. Now I work with ultra-high vacuum and I need to bring my molecule to the gas phase. Has anyone a rough idea how high the temperature ...
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Will addition of inert gas change the vapour pressure of a liquid?

From this question on Physics SE Thermodynamics of evaporation: Now imagine the experiment is repeated but instead of vacuum conditions, the water is pressurized with nitrogen at 1 atm. According to ...
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1 answer
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Relative humidity and vapor-pressure in equilibrium

I have quite an unclear understanding of relative humidity. I am writing my understanding on the topic and please correct me wherever I'm wrong: What I understood: Let's say $\ce{H2O}$ has a (...
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Partial pressure of gases in a container with a piston

I've been having problems with the following problem. Figure 1. A container with a piston like that shown in Figure 1 is filled with $0.10$ $mol$ of Ar and $1.00$ $mol$ of water (liquid and vapor). ...
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1 answer
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Can we compare the vapour pressure of solutions whose concentrations and temperature is known?

If we have some solutions, in which we know the temperature and concentration of the solute particles, can we compare their vapour pressures? Original question: Which solution has the highest vapour ...
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Does the composition of a solution keep changing when being boiled? [closed]

The mole fractions of the components of vapours aren't the same as those of the liquid-liquid solution (unless the solution is azeotropic), this implies a change in the composition of the liquid ...
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6 answers
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What is the difference between "vapour" and "gas"?

I have read the definition of vapour on Wikipedia, but I don't seem to have a clear idea about the difference between a vapour and a gas. I know what it means when it says, "gas at a temperature ...
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To calculate total vapour pressure of a solution

Question: 1 mole each of A and B were mixed to obtain an ideal solution of which one mole went to the vapour phase at equilibrium. If $P°_\mathrm{A} = \pu{100 torr}$ and $P°_\mathrm{B} = \pu{900 torr}$...
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-1 votes
1 answer
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Why doesn't relative humidity tend to 100%?

Relative humidity is defined as: $$\frac{\text{pressure of $\ce{H2O}$ vapours}}{\text{vapour pressure of $\ce{H2O}$ at that temperature}} \times 100$$ Suppose the temperature is fixed and I apply Le ...
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2 votes
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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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Depression of the Freezing Point

Recently we learnt that there is a depression in the freezing point when a non-volatile solute is added to the solvent. Our teacher explained this phenomenon with a graph where the vapour pressure of ...
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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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2 answers
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What affects the vapor pressure of a pure liquid? [closed]

So pretend we have two samples of pure benezene in equilibrium with its vapor. One sample containing 0.5 mol and one containing 1 mol. They're also both at the same temperature. Let's pretend they're ...
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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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XSteam IF97 tables (MS Excel version) lack of inputs [closed]

I am using XSteam IF97 to evaluate steam power plant cycles. However, I miss some important input options such as pressure as a function of entropy and temperature ("p_st()") - when I assume ...
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Why exactly does high pressure (72 bar) nitrous oxide's pseudocritical¹ temperature drop so far when oxygen is added to make 50%v/v mixture? (Entonox)

This answer to Can precipitation occur in states of matter other than liquids? mentions the unusual case of Entonox. The effects of temperature on nitrous oxide and oxygen mixture homogeneity and ...
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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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opening valve separating two volatile solutions [closed]

Let there be two containers A and B containing two volatile solutions (ideal) of pure liquids P and Q respectively. The containers are connected by a tube such that only vapours can travel through ...
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Why is water transferred from a beaker of pure water to a beaker of sugar solution when placed in the a closed container?

I know that there is something to do with the vapour pressure of pure water being higher than the vapour pressure of the sugar solution, but I still can’t really explain what happens on a molecular ...
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Why does Vapor Pressure decrease on addition of solute? [duplicate]

Consider a vessel with a volatile liquid in it. Let's say it has a vapor pressure $P^0$ when it is pure. Now a non-volatile solute is added to it. Its vapor pressure decreases as $P^0\chi_{solvent}$. ...
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When is Raoult's Law valid for solid-liquid solution?

Raoult's Law for solid-liquid solution is stated as such in my books that it is applicable for all non-volatile solutes. However different solutes must have different attractive or repulsive forces ...
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How do i experimentally determine the vapour pressure of a solution? [closed]

So i wanna dissolve different salts in water and measure the vapour pressure of the resulting solution. I am doing this to compare the freezing point depression of different cations, used with the ...
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