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.
222
questions
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1answer
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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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0answers
30 views
Why is vapour pressure not a surface phenomenon?
In my textbook, it is written that vapour pressure is not a surface phenomenon. But why? Clearly, vapour pressure arises due the evaporation of liquid molecules at equilibrium and evaporation IS a ...
2
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1answer
38 views
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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0answers
34 views
why is unsaturated vapor pressure of vapor present in certain volume of air is equal to saturated vapor pressure of that vapor at dew point?
According to my textbook,unsaturated vapor obeys combined gas law.So if temperature is decreased to dew point temerature,the partial vapor pressure should decrease.If so,why it is stated that the ...
3
votes
1answer
84 views
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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1answer
44 views
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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6answers
3k views
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 ...
3
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1answer
70 views
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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1answer
38 views
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 ...
2
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0answers
25 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 ...
3
votes
1answer
66 views
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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0answers
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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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0answers
33 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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2answers
128 views
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 ...
1
vote
1answer
49 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 ...
0
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1answer
57 views
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 ...
5
votes
1answer
336 views
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 ...
2
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0answers
25 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, ...
0
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1answer
28 views
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 ...
0
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2answers
159 views
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 ...
0
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3answers
237 views
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 $P^0\chi_{solvent}$.
...
0
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1answer
125 views
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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1answer
52 views
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 ...
0
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1answer
348 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 ...
0
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0answers
71 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 ...
4
votes
1answer
619 views
Detailed kinetic explanation for vapor pressure reduction by dissolved solute?
The following problem was asked in JEE Mains 2020 (Sept 2, Shift 1),
An open beaker of water in equilibrium with water vapor is in a sealed container. When a few grams of glucose are added to the ...
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0answers
40 views
Calculating the number of volatile molecules in a container of known volume [closed]
Is it possible to calculate the number of volatile molecules (so only those in the gaseous phase) in a container of known volume, if the vapor pressure of the compound is known? So for example, if you ...
3
votes
1answer
41 views
Vapors of Aqueous solutions
I'm dealing with a common photoresist developer TMAH (tetramethylammonium hydroxide) and attempting to design a vapor sensor for a sealed chamber. Now I havent been able to confirm what exactly is ...
0
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0answers
29 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 ...
2
votes
1answer
99 views
Vapour pressure and Raoult's Law
The following question from my textbook assignment reads
A mixture contains $1$ mole volatile liquid $A$ ($P_\mathrm A^\circ = \pu{100 mmHg}$) and $3$ moles of volatile liquid $B$ ($P_\mathrm B^\circ ...
2
votes
1answer
300 views
At what composition is Maximum deviation from Raoult's law observed?
Raoult's law states that in an ideal binary solution of two volatile components, the partial vapour pressure of each component is proportional to its mole fraction in the solution.
A plot of total ...
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0answers
39 views
What limits supersaturation in the absence of nucleation sites? [closed]
Imagine a scenario where we have a chamber with air that is supersaturated with water vapour. In this ideal scenario there are no nucleation sites (e.g no suspended particles or nucleation on the ...
0
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1answer
96 views
Latent Heat, Vapor pressure and Equilibrium [duplicate]
So after reading about this topic i wanted to share what i learned and i wanted you guys to tell me if what i am writting is correct:
A pressure vessel has propane inside and it is pressurized. The ...
0
votes
1answer
41 views
Relative humidity at constant temperatures [closed]
It’s known that Relative humidity = (water pressure in a certain volume/ saturated water pressure in the same volume)* 100% “at the same temperature”
So my question is why does the amount of water ...
2
votes
0answers
80 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 ...
1
vote
2answers
55 views
Shouldn't the pressure of gas above a liquid slightly decrease when some of its molecules dissolves in the liquid? [closed]
Lets say a liquid and gas above are in equilibrium.
(1) Now if I suddenly increase the pressure of the gas it will take some time for some molecules of the gas to enter the liquid and get dissolved. ...
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votes
1answer
119 views
Cross checking the fact that gas solubility decreases with temperature increase and Henry's law's validity
It is known that the solubility of gas decreases with increase in temperature which is due to the kinetic energy freeing the solute particles into the vapor phase. Henry's law states that the partial ...
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votes
1answer
368 views
Vapor Pressure and Boiling Point [duplicate]
I heard that the boiling point of a solution is the temperature where its vapor pressure at that temperature equals the atmospheric pressure at that temperature. Thus at higher altitudes, as the ...
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votes
1answer
30 views
Doubt about definition of boiling point [duplicate]
The definition of boiling point says boiling point is the temperature at which the vapour pressure of liquid becomes equal to vapour pressure of atmosphere. But how does the vapour pressure of the ...
1
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1answer
1k views
How is Raoult's law a special case of Henry's law and not vice versa?
I know that Raoult's law can be a special case of Henry's law when the value of the Henry's constant becomes equal to the vapour pressure of the pure state of the liquid. Why can't we say the opposite,...
1
vote
2answers
6k views
How much time liquid mercury takes to evaporate?
I asked before about a thermometer that I broke yesterday. To summarize, I broke a mercury thermometer in my bedroom, which is a place where is difficult to have sure that I get rid of all mercury, ...
0
votes
1answer
74 views
Vapour pressure of a liquid subjected to pressure
I am following the derivation by Atkins in section 4B(c) (Physical transformations of pure substances; thermodynamic aspects of phase transitions), in which the authors derive the equation ${p = p_* * ...
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0answers
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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 ...
0
votes
1answer
46 views
Does evaporation occur while boiling as well? [closed]
If evaporation were to occur when a liquid was being boiled, then the amount of liquid changing phase would also depend on the surface area of the liquid exposed to the atmosphere (as evaporation rate ...
0
votes
2answers
82 views
What is the vapor pressure of a liquid if it is not in a sealed container(i.e., a river or lake)? Is it just the atmospheric pressure? [closed]
From what I understand, the boiling point of a liquid is when its surrounding pressure is equal to its vapor pressure. The vapor pressure is the pressure of the gas form of the liquid in a container ...
3
votes
1answer
128 views
Reducing pressure in a binary liquid solution
Consider the following diagram for a binary liquid system comprised of A and B, where A is the more volatile component.
My professor says
Consider an isopleth from $a$ to $a_4$. At the start, the ...
0
votes
1answer
133 views
Vapour Pressure of A Solution
I study in class 12, and have a doubt in vapour pressure that my school teacher and my friends are not able to clarify.
My doubt is the reason why the partial vapour pressure of each individual ...
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0answers
127 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 ...
0
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2answers
215 views
Antoine law and ideal gas law
I have the following question:
A $100\ \mathrm{ml}$ sealed flask with $60\ \mathrm{ml}$ acetonitrile is heated to $140\ \mathrm{^\circ C}$. The boiling point of acetonitrile is $82\ \mathrm{^\circ ...
4
votes
0answers
49 views
can a vapour denser than air evaporate in a closed chamber? [closed]
Imagine a closed container filled with air.
There is some liquid substance on a bottle placed on the floor of the container.
Let's heat the liquid until it starts to evaporate. Let's say 20% of the ...
