21
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 ...
- 39k
21
votes
Accepted
Why is octane more volatile than water while having a higher boiling point?
One thing you are missing is that air contains water, but usually does not contain octane. So for water, the process is:
$$\ce{H2O(l) <=> H2O(g)}$$
and for octane, it is
$$\ce{C8H18(l) <=> ...
- 39.1k
18
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. ...
- 31k
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†....
- 31k
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 ...
- 35.4k
15
votes
Accepted
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/...
- 30.3k
14
votes
Why is octane more volatile than water while having a higher boiling point?
The are three major factors, affecting observed relative volatility, ordered by assumed importance:
The molar mass. The liquid with higher molar mass evaporates faster than a liquid with the same ...
- 39.1k
13
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 ...
- 31k
12
votes
Accepted
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 ...
- 67.3k
12
votes
Accepted
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 ...
- 30k
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 ...
- 20.8k
10
votes
Accepted
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 ...
- 17.4k
9
votes
Accepted
Why does the vapour pressure not depend on the surface area and volume of a liquid?
Vapour pressure is intensive property.
It depends for pure liquids (if we neglect minor secondary effects) only on temperature. Water molecules are not aware of the surface size nor the liquid volume ...
- 39.1k
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 ...
- 2,885
8
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\:...
- 12k
8
votes
Why does the vapour pressure not depend on the surface area and volume of a liquid?
Your intuition confuses the long term equilibrium level with how fast it is reached
Your intuition that a larger surface area should increase evaporation rate is correct.
But we normally define "...
- 35.4k
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 ...
- 30k
7
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 ...
- 10.1k
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 ...
- 12.4k
7
votes
Accepted
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 ...
- 39.1k
7
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 ...
- 179
7
votes
Accepted
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 ...
- 371
7
votes
Accepted
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. ...
- 12.1k
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 ...
- 179
6
votes
Accepted
Could compressed refrigerant be stored feasibly in residential setting?
I happen to have a bottle of refrigerant in my house and another in my car (besides the stuff already being stored in my AC units).
While this is definitely more of a physics question, or perhaps a ...
- 1,556
6
votes
Why is Diiron nonacarbonyl so exceptional?
Wikipedia (primary reference) suggests a possible reason for $\ce{Fe2(CO)9}$ dissolving preferentially in THF versus nonpolar solvents: it reacts according to the scheme
$\ce{Fe2(CO)9 + THF <=>...
- 53.1k
6
votes
Accepted
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 ...
- 30.3k
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".
- 40.2k
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