# 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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39 views

### 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 (...
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 ...
40 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). ...
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 ...
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 ...
45 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 ...
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 ...
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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### 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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### 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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### 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 ...
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 $\ce{HF}.$
129 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 ...
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 ...
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 ...
337 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 ...
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, ...
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 ...
160 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 ...
241 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 $P^0\chi_{solvent}$. ...
129 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 ...
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 ...
350 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 ...
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 ...
622 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 ...
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 ...
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 ...
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### 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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### 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 ...
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 ...
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 ...
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 ...
134 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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### 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 ...
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 ...