28
votes
Accepted
At what pressure will hydrogen start to liquefy at room temperature?
$\ce{H2}$ cannot be liquified at room temperature, whatever the pressure. Generally speaking, all gases can only be liquified when the temperature is under its critical value.
- 27k
24
votes
At what pressure will hydrogen start to liquefy at room temperature?
The critical temperature of Hydrogen is $\pu{32.938 K, resp. -240.21 ^{\circ}C}$. Above this temperature, it cannot be liquified.
So to answer your question, you can get as high pressure as you can ...
- 39.1k
22
votes
Aside from carbon, what other substances can be made "superhard"?
Interestingly, nobody addressed the reason why diamonds are hard in the first place. The pressure (and temperature) are not the reason why they're hard, only the reason why they are formed. The ...
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21
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Aside from carbon, what other substances can be made "superhard"?
Here are some compounds that have other structures, followed by their hardest structure (based on Moh's Scale).
Titanium dioxide: Rutile structure or Cotunnite structure
Aluminum oxide: Corundum
...
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12
votes
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Why do we use the external pressure to calculate the work done by gas
If the piston is frictonless and massless, then, if you do a force balance on the piston, you must have that the force per unit area that the gas exerts on the inside face of the piston will always be ...
- 13.1k
12
votes
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Does high pressure reverse reaction between zinc and sulfuric acid?
As a very rough estimation of pressure when the hydrogen redox potential equals zinc standard redox potential, we can use the extrapolation of the Nernst equation:
\begin{align}
E^\circ_\ce{Zn/Zn^2+} &...
- 39.1k
12
votes
Do gas particles colliding with each other affect the overall pressure?
Yes and no.
As a first approximation, a given gas molecule is roughly as likely to gain momentum than to lose momentum when colliding with another molecule. Thus once our molecule hits a wall, the ...
- 499
12
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Heat capacity of (ideal) gases at constant pressure
Statistical Thermodynamics
The rationalization of the specific heat capacity at constant volume being only a function of temperature, can be derived from combining quantum mechanics and statistical ...
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11
votes
What is "chemical pressure"?
External and internal pressure
To study the effect of pressure on properties of a solid, is equivalently to learn how changes in volume transform physical parameters. For external pressure at ...
- 7,021
11
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Accepted
Confusion in Van der Waals Equation
The van der Waals equation is represented as such:
$$\left(P + \frac{an^2}{V^2}\right)(V-nb) = nRT$$
Here, $P$ is the pressure of the container and $V$ is indeed the volume of the container. All the ...
- 1,227
10
votes
Accepted
Pressure exerted by a particle of ideal gas
Here's your confusion:
You need to consider two different things:
The momentum transfer per particle per collision. There, since we assume an instantaneous collision, it doesn't make sense to try to ...
- 12.1k
10
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Do gas particles colliding with each other affect the overall pressure?
The mutual collisions of real gas molecules do not have significant direct impact on the gas pressure.
The original thermodynamic notion of an ideal gas considers just wall collisions. Deviation of ...
- 39.1k
9
votes
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Can gaseous hydrogen and gaseous oxygen be compressed without reaction?
The study Explosion Characteristics of Hydrogen-Air and Hydrogen-Oxygen Mixtures at Elevated Pressures includes data for pressures up to 200 bar.
Data were collected for Hydrogen-Oxygen mixtures at ...
- 40.2k
9
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Will supercritical nitrogen stay supercritical if we raise temperature and pressure high above critical values?
If we maintain nitrogen at 220 bar and 400 °C, what will be the state of $\ce{N2}$? Will it be still supercritical?
Yes, it will still be supercritical. The only reasonable definition of "...
- 21.8k
9
votes
Accepted
Can silicon dioxide melt at 20 °C?
Question: Can $\ce{SiO2}$ melt at $\pu{20 ^\circ C}$?
According to experimental and calculated data values, my answer is no. See the phase diagram of pure silica based on the experimental and ...
- 39.5k
9
votes
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Is it possible to store moist air at high pressure?
There is one importing principle to consider.
Air does not store vapor. Space does. Less space means less vapor capacity, no matter how much of air is there. (*)
If air is being compressed, the ...
- 39.1k
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
Room-conditions supercritical fluids?
As you can see on this data page on Wikipedia helium-4 has critical pressure of 2.24 atm, but helium-3 has 1.13 atm, only slightly above atmospheric pressure. Hyperbaric chambers work with 1,3-1,5 atm,...
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8
votes
Why do helium balloons expand in volume as they go higher?
You are exactly correct that it is a matter of atmospheric pressure decreasing at a rate great enough to overcome the contraction due to decrease in temperature. On a nice, clear, dry 25°C day at sea ...
- 17.4k
8
votes
At what pressure will hydrogen start to liquefy at room temperature?
As others have said, hydrogen cannot be liquified above its critical temperature, which my source (Wolfram Alpha chemical database*) says is $\pu{32.97 K} = \pu{-240.18 ^\circ C}$
However, with ...
- 12.1k
8
votes
Accepted
Help with two containers problem, Xenon
I have calculated pressure in container one and that is p1 = 342817.92 Pa, and in container two p2 = 326979.2275 Pa. Then I have substracted this two values which gives me 15838.6925 Pa. After that I ...
- 39.1k
8
votes
Accepted
When styrofoam shrinks from pressure, why doesn't it go back to normal after decreasing the pressure?
The structure of styrofoam isn't as perfectly elastic as you think
Most styrofoam is created by various mechanisms that blow gases into the polystyrene matrix as it cools. One common process involves ...
- 35.4k
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
8
votes
Do gas particles colliding with each other affect the overall pressure?
The pressure in an ideal gas is only due to collisions with the vessel's walls, collisions between molecules do not contribute. This can be shown by considering general forces on a molecule using ...
- 30k
7
votes
Are diamonds really forever?
Well, it seems that diamond is not forever because upon exposure to sunlight it loses atoms.
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7
votes
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Van der Waals real gas equation
Let me begin my discussion by first introducing the notion, using some intuitive model building, and will try to derive, or perhaps guess the van der Waals equation of state.
The perfect gas ...
- 8,465
7
votes
Does exotic potassium exist?
First, a point that is more like a comment: I'm not sure that just because electrons get put in to d-orbitals (and thinking of crystal band structures in terms of atomic orbitals is of questionable ...
- 8,289
7
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Why is my solution for the partial pressures of two different gases incorrect?
The answer by camd92 is correct, but there is no reason to calculate amounts. According to the chemical equation, one third of the particles in the gas phase will be dinitrogen oxide, and two thirds ...
- 39k
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