# Tag Info

0

Short answer: the changing composition between silicate-rich mantle and iron-rich core means the melting temperature does not increase sufficiently for the iron/nickel outer core to remain solid. The ability of something to solidify is a competition between the potential energy associated with the atoms that would occupy a solid lattice versus the thermal ...

1

Slight radioactivity inside the earth continues to produce heat - and given the size of the earth, this heat cannot easily get out. As a result, the deeper parts of the earth are very, very hot (think volcanoes) - and most phase diagrams will tell you that at sufficiently high temperatures, most things are liquid. Entropy favors it.

8

The Earth has a liquid outer core, a solid mantle exterior to that, and a solid core interior to it! So that’s how come the Earth has the heaviest, densest elements at its core, and how we know its outer core is a liquid layer. Like all elements, whether iron is solid, liquid, gas or “other” depends on both the pressure and temperature of the iron. Iron, ...

1

Simple answers like "pressure keeps substances in solid state" are gross simplifications. If you look at any scientific source, a phase diagram often shows $p$ and $T$ (pressure and temperature) on the axes. This is because at different temperatures but at equal pressures, substances can have different states and vice versa for different pressures and ...

1

Why does a critical point even exist? I think this question is equal to this one: "Why the width of the two phase region is bigger at lower temperatures and pressures?" Specific volume of liquids mostly depends on the temperature of them in comparing with their pressure. This means, for a well-defined increment of the pressure, we can neglect its effect ...

2

Attempting to answer the "why" question intuitively: In a liquid, the molecules experience significant intermolecular force - so much so, that the average energy of the molecules is insufficient to escape the attractive force of the surrounding materials. The result is that it energetically favorable for them to remain close together, even if that means ...

14

I will try to answer these questions from different views. Macroscopic view The "quantitative" rather than qualitative difference in a liquid-gas phase transition is due to the fact that the molecules arrangement does not change so much (there is no qualitative difference) but the value of the compressibility changes a lot (quantitative difference). This ...

8

For a pure substance that can exist in the solid, liquid, and vapor states (i.e., wood is not in this category), let's assume that a closed container is half full of liquid and half full of vapor. As the temperature rises, the liquid expands and the liquid density falls. Also, as the temperature rises, the pressure in the container rises due to the vapor ...

2

Good question. I don't have my Widom around, but I'll try to answer from memory. I think the consensus is to say a substance is at its gas state if it could be a liquid at the same temperature. This, as opposed to same pressure, same volume, etc. If the temperature is supercritical, there is no transition between liquid and gas, and the generic term "fluid"...

2

Particle on a rotating ring For further discussion purpose, let's considere the dynamics of a quantum particle on a $r_0$ radius rotating circle at a constant angular velocity $\mathbf{\Omega}=\Omega\,\hat{e}_z$ . In cylindrical coordinates, we fix $z=0$, and we have the azimuthal angle $\theta$, which is the "good" degree of freedom describing the ...

0

Maybe you would like to trace over other base. For example, your interest eigenstate is $N-$ body state $|\psi\rangle$, then you have density matrix $\rho=|\psi\rangle\langle\psi|$, and to derive a single site's information you only have to trace over other state, i.e., $\rho_j=\prod_{i\neq j}\sum_{\sigma_i}\langle \sigma_i|\rho|\sigma_i\rangle$, and get a $... 1 Hot water seems to freeze faster than cold water, known as the Mpemba effect$^{[1]}$. The effect was named after the Tanzanian student who in 1963 noticed that hot ice cream mix freezes faster than a cold one. The effect was first observed by Aristotle in the 4th century BC, then later Francis Bacon and René Descartes. Erasto Mpemba published a paper on ... 4 This phenomenon you are describing is called the Mpemba effect after a Tanzanian student, Erasto Mpemba, who in 1963 noticed the temperature of ice cream affected how quickly it mix freezed, though the effect had been observed much earlier (the earliest known observation of this was by Aristotle in 4 B.C, though Aristotle probably didn't use ice cream). ... 0 There is no spontaneous symmetry breaking at the water-gas phase transition, because it's a first-order transition and symmetry breaking typically happens at second-order phase transitions. Physicists usually think of a phase as a region of parameter space that's connected by paths that don't cross any phase transitions, so a physicist would indeed say that ... 2 This answer may be incomplete, but I hope it will help you anyway. In Landau's book Statistical Physics (chapter XIV, phase transitions of the second kind and critical phenomena), the author writes the Gibbs free energy$\Phi$as a function of$T,P,\eta$, where$\eta$is the order parameter: $$\Phi=\Phi(T,P,\eta)$$ He then states that$\eta$is different ... 2 First some preliminaries. There is, in general no requirement that a thermodynamic system should have exactly 2 degrees of freedom. The fundamental thermodynamic equation has the form $$dU = TdS + \sum_{i=1}^{n-1} F_i\,dX_i$$ Where$F_i$and$X_i\$ are the generalised forces and generalised displacements. Each term in the equation introduces 2 variables ...

1

I think the answer is "no" in the case of NaCL (which is what we usually refer to as "salt"). Here are the arguments: First - the dissolution of (NaCl) salt in water is slightly endothermic (5 kJ/mol), but the dissolution of salt in ice is much more endothermic. This is nicely explained in this answer: adding salt to ice creates "ice above its melting point"...

0

Salt causes the ice to melt at a lower temperature, but it also lowers the vapor pressure of the resulting liquid. This would result in a SLOWER rate of water turning into vapor, not a higher rate, because both sublimation and evaporation are directly dependent on the vapor pressure of the substance that is involved, and also on the partial pressure of that ...

1

From the book Freeze Drying by Georg-Wilhelm Oetjen: Oesterle showed that not only can tBA speed up the sublimation of ice from amorphous freeze-concentrated mixtures, but also similar effects can be achieved with volatile ammonium salts such as ammonium acetate, bicarbonate and formate. In other words, a scientist showed via experimentation that ...

0

As Floris mentioned sublimation is only from solid directly to vapor. When the water turns into vapor the salt will be left behind so the total energy transferred to the water from the environment will be the same as without the salt. However, when the solid turns into a liquid it will spread out into a puddle. When the liquid is spread out it's surface area ...

5

Nothing in the laws of thermodynamics forbids multiple liquid phases for a single substance. The only limit is the simultaneous coexistence of at most three phases (at triple points). Water has a solid-liquid-gas triple point and several soid-solid-liquid and solid-solid-solid triple points; see the phase diagram of water and ice. In addition, although not ...

1

There is actually only one disordered phase - from a physicist's perspective, the liquid and the gas are actually the same phase because one can continuously vary the external parameters (temperature and pressure, in this case) to get from the liquid to the gas without passing through any phase transition, because the phase transition line terminates within ...

14

The most immediate answer would seem to be that a great variety of different crystal phases can exist because their long-range order makes it possible to classify them based on the different symmetries of their lattice structure. Since the liquid (or amorphous solid) phase only has short-range order and the gaseous phase doesn't even have that, it seems ...

Top 50 recent answers are included