# Tag Info

26

The carbon phase diagram shows that liquid carbon is only achievable at high pressure (~100 atm) and high temperature (~4500 K). This means that liquid carbon probably has very limited applications, and not many will be researching it. Funding is hard to come by when the applications of the research are not apparent. Image source

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“Surprisingly a web search did not answer these questions” — Well, a web search for liquid carbon turns a few results: A 2005 study of liquid carbon by x-ray absorption spectroscopy (second Google search result) (the paper itself): low-density liquid carbon contains predominantly twofold-coordinated chain structures (sp hybridization). As the density ...

16

It's just about heat capacity + heat conductance, nothing more. $\ce{CO2}$ sublimates much quicker in the water because water is much better at heat exchange than air. Anybody who ever experienced swimming in water at 15°C and walking in air at 15°C can attest to that. Catalysts for heat exchange are usually made of copper and other metals. (Also, usually ...

12

Naphthalene, as well as any other solid, may sublimate at any temperature and pressure. The triple point parameters are irrelevant. The pressure of other components (that is, air) is irrelevant as well. What is relevant is the vapor pressure of naphthalene itself in the surrounding air, and that is pretty close to $0$. Until it reaches the saturated vapor ...

11

As long as there is less than 100% relative humidity, the ice will sublime to some extent. Just in the past week it has been in the -12 °C to -5 °C range in my area, and the snow and ice on the ground did sublime, on the order of 1 cm per day, more in the sun less in the shade. For quantitative information see "Sublimation from a seasonal snowpack at a ...

8

Iodine sublimes for the same reasons that all solids do: because it has some equilibrium vapor pressure an normal conditions. Now, the value of that pressure varies greatly in different solids. For many of them, it is so extremely low that for all practical reasons it can be considered non-existent. (Say, if you'd leave a sample of NaCl for a thousand years, ...

7

Have a look at a generic phase diagram, for a compound with one solid phase, one liquid phase and a gas phase:              For the solid to go directly into the vapor phase (sublimation) at ambient pressure upon heating, you thus need its triple point to have a higher pressure than atmospheric pressure, i.e. ~1 bar. Looking at this partial table of ...

7

Look up the term “phase diagram”. At different temperatures and pressures different phases are favored. Think about water. At 0 °C and 1 atm water and ice are equally favorable. There can be freezing or melting. At other temperatures and pressures there can be sublimation and deposition. The sublimation of water is involved in freeze drying and freezer burn ...

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I think your question can be more generally stated, and subsequently, answered. Why do some substances sublime, while others don't? To understand this, you need to understand a phase change to gas occurs when the total vapor pressure of substance in a condensed phase (solid or liquid) exceeds the atmospheric pressure. [In case you aren't familiar with the ...

4

Iodine vapors combine with iron to form iron(II) iodide:$$\ce{I2 + Fe->FeI2}$$ In an anhydrous form the compound is dark red-purple. But iron(II) iodide is hygroscopic and deliquescent which means that it dissolves in moisture it absorbs from the air, and forms those droplets. This complicates a bit the chemistry of the droplets - the $\ce{Fe^2+}$ ion ...

3

This sounds like a nice project. For the purification of caffeine, sublimation in vacuum and recrystallization from ethanol are both conceivable. But first you have to separate it from the other ingredients, such as carbohydrates. According to the manufacturer, 100 mL of Red Bull, a popular brand, contain 11 g sugars and 32 mg caffeine. In order to ...

3

To answer part 1 of your question: It is correct to call the change form solid to gas below the equilibrium vapor pressure sublimation. And there is no separate term for vaporization of a solid above the equilibrium vapor pressure; it is still sublimation. Similarly, a boiling liquid is still perfectly correctly said to be evaporating. To answer part ...

3

Solubility of $\ce{CO2}$ in water is $\pu{1.45 g/L}$ at SATP. Apparent dissociation constant for carbonic acid at the same conditions is $K_\text{a}(\ce{H2CO3}) = \pu{4.47e−7 mol L^{-1}}$. Now lets speculate how much dry ice could be disposed and what the pool capacity might be, guessing that the water warmed back up. It's hard to tell which pool size your ...

3

Yes, the thing you smell surely does lose some molecules, and consequently some weight. It can be said that it slowly evaporates or sublimates. But the strength of smell varies greatly in different compounds, as does the rate of evaporation (sublimation). Some compounds may be gone completely in a few minutes, and some would stay for years, or even decades.

3

Sublimation refers to molecules passing from the solid to the gas state without going through the liquid state. This happens all the time to every solid, including water, it's just a question of at what rate it sublimes and how that rate compares to its rate of melting in the same conditions. Snow, for example, often noticeably sublimes instead of melting, ...

3

To a first approximation, any pure substance can sublimate. However, complex substances may decompose or change their structure before any appropriate sublimation conditions are reached. The only (and very remarkable) exception is helium (in fact, helium is so special that helium-3 and helium-4 have quite different phase diagrams even though they're ...

3

Well, you see, searching online for "vapor pressure at such-and-such temperature" (or conversely, "temperature to get such-and-such pressure") is often fruitless, and unnecessary too, because pretty decent approximations are known. Here is one: $$\ln\mathfrak p=-{\Delta H\over R}\left({1\over T}-{1\over T_0}\right)$$ where $\mathfrak p$ is your vapor ...

3

The gas flows downwards because it is more dense. It is more dense both because $\ce{CO2}$ is heavier than $\ce{N2}$ and $\ce{O2}$ and because the gas is colder than the ambient air. The mist is water in the surrounding air condensing into microscopic droplets due to the lowered temperature. The amount of mist depends on the humidity of the air; in ...

3

Evaporating liquids and sublimating solids have temperature lower than the surrounding. That is because the most energetic molecules escape to gaseous phase, cooling down the condensed phase, as it's average energy per molecule decreases. The standard psychrometric method of air humidity measurement, used in meteorology/climatology, is based on this ...

2

It looks to me like tubes used to distribute gas flow. If you work with substances that would react with the oxygen in air, you prevent that by working under an inert gas such as nitrogen, i.e. you fill all the flasks containing your substance with nitrogen gas, keeping up a steady flow of the nitrogen in order to prevent any from air leaking in. The ...

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Yes you can because it is in a complex with the povidone. You just have to heat it a little bit extra. This is because a complex is "tangled up" molecules. In this case it is Povidone and Iodine. Nile Red used a different process (liquid-liquid extraction), but here is the link. https://www.youtube.com/watch?v=FNf8PSda7iI

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A procedure is available on Erowid for this process. Make or buy a coldfinger (see below), boil your fluid to absolute dryness, without burning the dry restant, then hang your coldfinger in an appropriate Erlenmeyer, and heat gently the now dry restant. Make your coldfinger fat-free with acetone first (on the outside where the I2 will condense). The I2 ...

2

The vapor gradient reflects the fact there is much more space at the corner than in the middle of a face. The vapor builds up near the surface but because there is much more space near a corner, the vapor pressure drops off, where as the vapor pressure near a point on the middle of a face is reinforced by sublimation at points near it.

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Yes iodine's good leaving group. the leaving ability is best described by the Gibbs energy change that occurs. So since chlorine is a poor leaving group so that make the reaction slower as less energy is available. So I think that you are right so far.

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At the very least your pressure has to be consistent with a whole number of molecules or atoms in your vapor phase. Suppose you have a pressure of $7×10^{-34}$ atmosphere or (roughly) $7×10^{-29}$ Pa at $300$ Kelvins. The average volume per atom/molecule is computed by the molecular level version of the Ideal Gas Law, in which the gas constant $R$ per mole ...

2

Can we justify that "For sublimation of a solid at 1 atm $\Delta U>0$ at low temperature and $\Delta U<0$ at high temperature?" No. $\Delta U>0$, always, for sublimation, because of the energy needed to separate the atoms or molecules in changing from the solid to the gas phase. As for the enthalpy, H = U +PV \Rightarrow \Delta H = \...

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MIT has a brilliant technique for sublimating and condensing: https://www.youtube.com/watch?v=dBNELFi5XiY The sample is placed in a culture dish sitting on a hotplate. The lid is placed on top. Finally a beaker with ice is placed on top of the dish to condense the sublimate. After a while crystals form on the top of the lid. These pure crystals are ...

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By definition, going from solid to gas directly is sublimation. If moth balls were not solid, but liquid instead, then we'd call the process evaporation.

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I got my answer at wikipedia after a little through study, it goes like this - Evaporation that occurs directly from the solid phase below the melting point, as commonly observed with ice at or below freezing or moth crystals (napthalene or paradichlorobenzene), is called sublimation. So it is actually evaporation but called sublimation source:https://en....

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Percent recovery if sublimate is not 100% complete since the fumes may be blown away especially if not executing proper sublimation process.

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