# Tag Info

3

Simply Said: It doesn't attract itself enough to be solid. So much resistance to attraction that it is very hard to liquefy. The electrons prefer to repel because the electrons repel like the protons.

4

Throttling the gas (Joule-Kelvin expansion) only lowers the temperature of the gas when the Joule–Thomson coefficient is positive. For Helium, that point (the "J–T inversion temperature") is reached at 43°K (source: Cryogenic Society of America; the wikipedia article gives an incorrect value of 51°K). Above that temperature, Joule-Kelvin expansion will ...

3

For the first question, it is the low boiling temperature, 4.21K for Helium-4 and 3.19K for Helium-3, that makes helium difficult to be liquefied. Hydrogen's boiling temperature at 1 atm is 20.27K, or about 4-5 times higher. For pre-cooling, one can take a look of entropy $$\delta S = \frac {dQ}{T}$$ We can see that, because T is very small, a slight ...

46

The next approximation beyond the ideal gas is given by the Van der Waals fluid equation. It is a phenomenological law which takes into account the finite size of the molecules and their interactions with themselves. When you plot several Van der Vaals isotherms for a given substance, you observe that some of them show a phase transition from gas to liquid ...

21

Getting from gas to liquid is a matter of interparticle interaction winning over thermal agitation. There are several reasons why interparticle interactions are very weak in the case of helium atoms. On one hand, it is a noble gas and thus cannot form covalent bonds. On the other hand, it is very light hence highly non-polarizable: its Van der Waals ...

2

For the hypothetical case of a thermally perfectly insulated system, I'm sure you can work out yourself from the specific heat and the enthalpy of fusion for water. Given that the enthalpy of fusion (330 kJ/kg) and the specific heat of ice (2 kJ/kg-K) have a ratio of 165 K, and you need the entire ice bucket to stay below the melting point, and your 20:1 ...

1

Whether something is solid or not, generally depends on two things: the attractive forces between molecules/atoms and the temperature. The attractive forces will try to lock the molecules together and make it harder for the material to change shape (or being solid), but this can only happen when the molecules aren't moving fast. If they are moving too fast, ...

1

Molecules of solid object are still able to move and can even move in high speed if the object in high temperature . Being solid only mean that those molecules is hard to separate or make room ( like liquids does ) ,it doesn't mean those molecules have to be standing still . That what I think . Sorry for my bad English

3

Solid and cold are two distinct concepts. As you can change the state (solid, liquid) with temperature (cold, warm), there must be a relation to it. For each degree of freedom you have a thermal energy of $k_\mathrm B T/2$. Atoms in a crystal have a certain binding energy. If the thermal energy is way larger than the binding energy, no crystal can form. If ...

0

You know that sound is a longitudinal wave. It passes through a medium by pressurizing and depressurizing the medium. Solids are highly elastic than air. They are very hard to deform. So, they resist any change in the positions of the atom. Once disturbed, the medium develops a high restoring force to tend back to it's original position, but inertia causes ...

2

Adiabatic bulk modulus of air $=1.4\times 10^5$ Pa and Young's modulus of steel $=1.8 \times 10^{11}$ Pa. Density of air $= 1.2$ kg m$^{-3}$ and of steel $8050$ kg m$^{-3}$. The interaction between the atoms within steel is via the bonds whereas the interaction in air are by molecules colliding with one another and limited by the speed at which the ...

0

I've been wondering about what makes things melt versus light on fire, or why somethings burn at some temperature rather than melt(or vice versa) maybe I started off thinking of things burning or melting on a pan. I had this same line of thought to a large extent--some things will just melt at some temperature before they burn, but other things seem as if ...

2

The primary difference is that the electrons in metallic hydrogen are nearly completely degenerate. Degenerate electrons cannot be dissipatively scattered and lead to the "metallic" characteristics of extremely high electrical and thermal conductivity. To first order, to produce metallic hydrogen you need to make sure that the electron kinetic energy at ...

2

In metallic hydrogen, the protons share an approximately fixed location relative to each other - energetically, a lattice is more favorable than an randomized state. Because of this, the substance is not a plasma - in a plasma, the positive and negative charges both flow freely. Metallic hydrogen only exists at very low temperatures, and very high ...

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