28 votes
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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.
Maurice's user avatar
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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 ...
Poutnik's user avatar
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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 ...
David LUC's user avatar
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21 votes

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 ...
CoffeeIsLife's user avatar
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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 ...
Chet Miller's user avatar
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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+} &...
Poutnik's user avatar
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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 ...
Wrzlprmft's user avatar
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12 votes
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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 ...
Metal Storm's user avatar
  • 3,036
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 ...
Linear Christmas's user avatar
11 votes
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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 ...
thelocalsage's user avatar
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10 votes
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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 ...
theorist's user avatar
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10 votes

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 ...
Poutnik's user avatar
  • 41.3k
9 votes

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 "...
Curt F.'s user avatar
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9 votes
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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 ...
Mathew Mahindaratne's user avatar
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 ...
Poutnik's user avatar
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9 votes
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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 ...
Poutnik's user avatar
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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 ...
airhuff's user avatar
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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 ...
theorist's user avatar
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8 votes
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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 ...
Poutnik's user avatar
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8 votes
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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 ...
matt_black's user avatar
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 "...
matt_black's user avatar
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 ...
porphyrin's user avatar
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7 votes

Are diamonds really forever?

Well, it seems that diamond is not forever because upon exposure to sunlight it loses atoms.
patricoo's user avatar
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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 ...
getafix's user avatar
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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 ...
Jon Custer's user avatar
  • 8,509
7 votes

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 ...
Karsten's user avatar
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7 votes

Pressure-dependence of electrolysis voltage

Of course, we're starting by acknowledging a perpetual motion machine is impossible. The question, then, is how do we understand, through chemical thermodynamics, why your specific set of steps can't ...
theorist's user avatar
  • 12.1k
7 votes

Regarding units of water potential and chemical potential

According to German Wikipedia water potential is defined as $$\psi := \frac{\mu - \mu_0}{\bar{V}},\tag{1}$$ where $\mu_0$ is the standard chemical potential (usually pure water at atmospheric pressure ...
andselisk's user avatar
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7 votes

Does high pressure reverse reaction between zinc and sulfuric acid?

Any equilibrium calculation involving ordinary compounds that gives a pressure of $10^5$ bar or more is probably not realistic. Chemical bonds can deform and rearrange under such pressures and thus ...
Oscar Lanzi's user avatar
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