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6
votes
1answer
84 views

Does everything exist as a gas at P = 0?

Attached is a phase diagram for carbon dioxide. At P = 0, it appears that the substance will exist as a gas regardless of temperature. My questions are: For any liquid at a fixed temperature, is ...
12
votes
2answers
684 views

How many molecules does it take to have a phase?

A single molecule can't be solid, liquid or gas. It's just a molecule. A mole of something can be any of the three. So, how many molecules does it take for phases to be meaningful? I realize that ...
0
votes
1answer
42 views

What happens when ice melts?

What happens when ice melts? I have this question, with two possible answers: regularly arranged molecules change into irregularly arranged molecules water molecules become less densely packed ...
5
votes
3answers
877 views

During a phase change in matter, why doesn't the temperature change?

I was working on something in school and came across the question: "Why do you think the temperature does not change much during a phase change?" I'm really not sure why this happens in matter ...
0
votes
2answers
48 views

How to figure out which phase in The Phase Diagram will have more density?

If I am given Phase Diagram and asked to determine which phase will have more density? What to consider to solve this kind of questions is it about thr area that each phase occupies? the more area a ...
3
votes
1answer
46 views

How do I seperate graphite powder from light oil?

I have a sample of very fine graphite powder suspended in light oil. I've attempted to seperate the two by placing the mix in a 2 micron filter sock. The oil will slowly drip through. If I apply ...
1
vote
1answer
31 views

Meaning of Cu1.5Al in Cu-Al phase diagram (I understand all other indexes incl. fractions like Cu0.75Al0.25)

I understand Cu0.75Al0.25 - that's just 75% Cu, 25% Al. I understand integer indexes - that's a normal chemical formula after all. However, I have no idea how to interpret Cu1.5Al, I've never seen a ...
0
votes
1answer
60 views

Liquefying butane in a freezer

If I were to put a can of liquid butane which is under pressure (eg. Lighter refill) in a freezer to get it below its boiling point of $-1^\circ C$, If it were released in an also frozen container ...
0
votes
1answer
31 views

Behaviour of water at exactly 0°C

If I had a beaker of water (i.e. many molecules), at exactly $0^{\circ}C$ and at atmospheric pressure, what phase would be encountered? And would the answer to this also apply to other substances at ...
1
vote
2answers
61 views

How can a phase be thermodynamically stable at room temperature if it only appears at high temperature?

How can a phase that appears at high temperature be thermodynamically stable at room temperature? For example, $\alpha$-alumina is a phase that is formed at temperatures above $1000^\circ C$. How is ...
0
votes
0answers
55 views

Eutectic Phase Diagram and Lever Rule

Question: A solution having composition $p$ (left side of graph) is cooled to just above the eutectic temperature (point $s$ is at $ .18 \; x_{Si} $ and the corresponding tie line intersects the ...
3
votes
3answers
194 views

Hygroscopic behaviour of DMSO - how bad is it?

For a fluid flow experiment I am using DMSO (dimethylsulfoxide), because of its low volatility, reasonably high surface tension, low viscosity and relative safety. In the MSDS of DMSO I find that the ...
3
votes
1answer
69 views

Phase transition from gas to solid

Link to question paper The question says: The phase transition from gas to solid is called (A) condensation. (B) evaporation. (C) polymerization. (D) sublimation I am pretty sure the ...
2
votes
1answer
56 views

How does the activity of Sn chemical potential vary as a function of composition at 900 C?

This is referring to the Cu-Sn phase diagram in which composition varies along a horizontal line at a certain temperature. I understand that as you move along that line different intermetallic or ...
1
vote
1answer
45 views

Phase stability of alcohols

Tert-butyl alcohol seems unusual among alcohols in that its melting point is high (25°C) while its boiling point is also still low (82°C). I am looking for more materials with phase-unstable liquid ...
5
votes
2answers
2k views

Why does water evaporate at room temperature?

When water temperature reaches $100^\circ C$, the molecules get so excited that the hydrogen atoms lose the bonds to the oxygen atom and therefore the water starts to become gas. I get that, but at ...
2
votes
0answers
1k views

Caffeine boiling and melting points

According to both caffeine's pubchem page and chemspider page its boiling point lies at 173°C and its melting point at ~235°C. How can it melt at that temperature if it already sublimated at 173°C? Or ...
1
vote
0answers
58 views

Phase diagram analysis

The figure is a portion of the titanium copper phase diagram for which only single-phase regions are labeled. Specify all temperature composition points at which eutectics, eutectoids, peritectics and ...
1
vote
2answers
147 views

Can these changes be reversed by changing temperature?

An egg turning hard when boiled. A spoon full of batter cooking on a hot griddle. I said that they both cannot be reversed, because I think if you throw both the egg and batter into the freezer, ...
1
vote
2answers
215 views

Why is water evaporation not more commonly used to cool buildings [closed]

Water has a very high heat of vaporization (2260 kJ per kg). Why not just gradually sprinkle water on your roof to keep the building cool in opposed to using air conditioners? It wouldn't take much ...
4
votes
1answer
213 views

Which elements have no liquid form at atmospheric pressure?

Carbon has no liquid form at atmospheric pressure. Is this unique amongst naturally occurring elements? The more interesting and vague question is, is this property somehow important or related to ...
5
votes
3answers
293 views

What non-toxic non-water substances have a freezing point very close to water's?

I was linked to a Kickstarter for a cooling ball to be placed in drinks which claims with constant marketing hyperbole how much it relies on "Phase Change" ! which is a neat concept and seems not ...
2
votes
1answer
53 views

Why do molecules have to first transform to gas before doing a reaction?

I have to calculate the enthalpy of the reaction $$\ce{Cs(l) + 1/2I2(s) -> CsI(s)}$$ and the answer is $$\Delta H_f = \Delta H_{vap}^{\ce{Cs}} + \frac{1}{2}\Delta H_{subl}^{\ce{I2}} + ...
6
votes
1answer
1k views

Why is the carbon dioxide we exhale transparent?

Why is carbon dioxide that comes from dry ice opaque and smoky while the carbon dioxide that we exhale transparent?
6
votes
3answers
10k views

How can melting point equal freezing point?

I don't understand how melting point = freezing point. For example, if liquid water freezes at 0*C how can ice also melt at 0*C?
2
votes
1answer
619 views

Why does heat solidify cake batter?

Increased vibration causes the atoms in an object to spread out farther away. Thus, with added heat, and object goes form a solid to a liquid to a gas (and then to plasma, with enough heat). Why is it ...
1
vote
1answer
43 views

What determines a substance's energy of activation with air?

Ice will melt when heat is applied; paper will catch fire. In trying to figure out why — what the difference is between things that melt and things that catch — I found "Burn, Char, Melt" by Roberto ...
4
votes
1answer
448 views

Why does water become less dense when it cools

Most materials become more dense as they cool, but ice floats in water, meaning that it's less dense. Why is this?
5
votes
1answer
465 views

What defines matter's phase at room temperature?

So, a simple question: what makes neon a gas; what makes water liquid; what makes plutonium-238 a solid at room temperature? Of course, the phase is determined by the excitation of the molecules, but ...
5
votes
1answer
103 views

Lennard Jones liquid vapor phase transition

I am trying to generate a phase diagram of pressure versus temperature in a NPT ensemble using molecular dynamics method. I am using the Lennard Jones potential with 108 particles and Berendsen ...
5
votes
1answer
233 views

Does sublimation happen only on the surface or throughout the body?

Like evaporation happens only on the surface of a liquid, and boiling/vapourisation takes place throughout the body, how does sublimation occur? Why?
2
votes
4answers
515 views

Phase diagram for first 10 elements

I've been looking on the net for a reference which shows a phase diagram for elements at least from $\ce{H}$ up to $\ce{Ne}$. Specifically, I'm looking which of these elements can be solid or liquid ...
3
votes
4answers
5k views

What is the difference between melting and dissolving?

What is the difference between melting and dissolving? I am looking some general features. The answer should be adaptable to the melting/dissolving of ice cube (water) in a class of pure alcohol ...