19 votes

What is the difference between "vapour" and "gas"?

Vapor is a much older word alluding to dampness and it was not coined by scientists. It is in use since the 1300s. The actual meaning of meaning of vapor is "Matter in the form of a steamy or ...
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17 votes
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How does Ostwald-Walker method work?

How are the vapors transported? The additional question from the comments: Why [is] the amt. of vapours taken up proportional to vapour press. Why directly proportional? Why not nothing else? ...
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17 votes

Vapor pressure and boiling point for solutions in open containers

Boiling is not about the upper surface at all. What happens there is but of little interest to us. Boiling means that bubbles are forming at the bottom and probably within the bulk of the liquid. ...
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15 votes

Is it possible to boil a liquid by just mixing many immiscible liquids together?

Yes they will boil all right. Sure, there might be some kinetic impediment to it if you let the liquids to settle in layers, but if you stir them so as to expose their surfaces, they will boil†....
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15 votes

What is the difference between "vapour" and "gas"?

The normal use distinguishes "vapour" from permanent gas At normal lab conditions there is a (fairly obvious) distinction between things that could exist as liquids and things where no ...
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15 votes
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Are molecules exchanged between a solid and liquid in equlibrium?

Even two solids in contact may exchange atoms, such as gold in contact with lead. Accidental cold-welding is a serious problem in space technology, in particular. You can prove to yourself that ice/...
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14 votes
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How to calculate melting/boiling points at different pressures?

I don't believe there is an equation that you can use for melting points of a general substance as a function of pressure (since the melting phase transition has a lot to do with the geometry of the ...
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12 votes
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How is volatility useful in the production of acids?

Yes, this is indeed the case. The reasoning behind it is using chemical equilibria to their fullest. If you have a Brønsted acid and a Brønsted base in the same vessel, you will always have an ...
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12 votes

Vapor pressure of immiscible liquids

This is not just some vapor pressure. This is the equilibrium vapor pressure. Thermodynamics is all about equilibrium, you know. And equilibrium, roughly speaking, is what takes place in a closed ...
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11 votes
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the chemical mechanism for deviations from Raoult's law

First some general comments about Raoults law before discussing the particular solutions in question. Raoult’s law suggests that the partial pressure of each substance above a solution is ...
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11 votes

What is the difference between "vapour" and "gas"?

I'm surprised the OED has such a strict definition for gas. I could not find a strict definition in the IUPAC color books (certainly not in the gold book). Presumably these words are in such common ...
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10 votes
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What causes the lowering of vapour pressure in volatile/nonvolatile solvent mixtures?

I think that the second explanation is the correct one. A simple experiment can prove it: if you place a porous cover over the pure solvent, its vapour pressure will not change. In alternative, you ...
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10 votes

The effect of air pressure on the melting point

For most substances, higher pressure (or air pressure, in your case) will cause the melting temperature to go up. To think about it intuitively, imagine that you have a certain solid. Melting it would ...
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10 votes
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Vapor Pressure Paradox

Although "paradox" is not quite the right term, what you have discussed is actually a simple, yet interesting and important phenomenon. Given the ideal situation as you have presented, your ...
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8 votes

Is it possible to boil a liquid by just mixing many immiscible liquids together?

Nothing special would happen, immiscible liquids would just form layers. As for the expression, $$p_T=\Sigma p^o_i$$ I suggest you read this answer. Quoting Ivan Neretin: This is not just some vapor ...
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7 votes
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Is sublimation a property of all substances?

Look up the term “phase diagram”. At different temperatures and pressures different phases are favored. Think about water. At 0 °C and 1 atm water and ice are equally favorable. There can be freezing ...
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7 votes

Reason for the formation of azeotropes

A solution that has a maximum or minimum vapour pressure (vs mole fraction) is called an azeotrope. The liquid is in equilibrium with the vapour and mole fractions in the liquid are the same as in ...
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7 votes

Is it possible to boil a liquid by just mixing many immiscible liquids together?

Is it possible to boil a liquid by just mixing many immiscible liquids together? No*, boiling is when the vapor pressure of a phase is greater than the ambient pressure. You might create a total ...
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7 votes
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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)

Dissolution(solvation) is solvation of solute molecules by molecules of solvents. This decreases chemical potential $\mu={\left(\frac{\partial G}{\partial n}\right)}_{T,p}$ of the solute, comparing it ...
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7 votes
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What is the difference between "vapour" and "gas"?

tl;dr– "Gas" and "vapor" aren't mutually exclusive. Generally: a gas is any material that'd fill a volume to its boundaries; and a vapor is a gas-like material that's ...
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7 votes
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Will addition of inert gas change the vapour pressure of a liquid?

If the nitrogen is truly inert, its presence will have no direct effect on the chemical potential of the water in the gas phase. Essentially, the gaseous water is "unaware" of the nitrogen. ...
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  • 11.6k
7 votes

Some salts lower the vapour pressure of water - do any raise it?

Chemistry is very complicated and I'm probably missing certain edge cases, but I think the answer is almost certainly 'no'. Salts lower the vapour pressure of water because intermolecular forces ...
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6 votes

Reason for the formation of azeotropes

Before getting to the azeotropes, it's worth reminding ourselves of the relevant assumption that we make about ideal mixtures: that the intermolecular interactions have constant energy regardless of ...
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6 votes
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When heat is increased, does water move upward in a straw due to increased capillary action or increased pressure?

It almost certainly was due to thermal expansion of water and the air above it. Consider that the thermal expansion coefficient of water near room temperature is ~$0.000214$ K$^{-1}$. [Though it is ...
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6 votes

A chamber to control concentration of a vapor: Is there a name for this equipment?

There is a book The Design of Controlled-atmosphere Chambers for the Study of Oxygen Toxicity, so I suggest "contolled-atmosphere chamber".
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6 votes
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What happens with the boiling point of a liquid in a vacuum

"Sealed in a vacuum" is an oxymoron, a contradiction in terms, much like "frozen with fire". If you seal a liquid in a flask containing nothing else but vacuum, then a part of the liquid will quickly ...
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6 votes

How much time liquid mercury takes to evaporate?

I found this statement in a paper about $\ce{Hg}$ contamination from dental work: The evaporation rate of elemental mercury at room temperature ($\pu{20 ^\circ C}$) is approximately $\pu{50 \mu g\:...
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  • 11.4k
6 votes

What is the difference between "vapour" and "gas"?

In college, I had a thermodynamics teacher who was awesome. He had a way of explaining things that were accurate and easy to understand. He explained this difference to us this way: A gas will not ...
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