An entity of a material system which is uniform in chemical composition and physical state. This tag should be applied to question regarding chemical and physical properties of phases, systems of phases and also phase transition processes.

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2answers
39 views

Structures present in liquid water

I know this may be a too generic question, but here it goes anyway. It is already know that solid water (ice) organizes its molecules in a lattice (in a variety of 16 different crystals and one ...
4
votes
2answers
280 views

Why does water change phase so easily?

I did some undergraduate level Chemistry as part of my degree. It left me with the distinct impression that the polarity of water is responsible for its unusual phase properties: it's the only ...
33
votes
7answers
7k views

Is toothpaste solid or liquid?

My teacher didn't answer this properly: Is toothpaste solid or liquid? You can't say toothpaste is a solid because solid material have a fixed shape but toothpaste doesn't. However, you can say ...
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vote
2answers
32 views

What's sulphur's state of aggregation in petroleum?

Using google, I wasn't able to find an answer to this question. Conditions: p = 1 bar and T = 298 K.
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votes
1answer
62 views

Why does the freezing point of a sample gas occur at a certain temperature?

From "North Carolina Measures of Student Learning: NC’s Common Exams Chemistry" (Source, Number 20): The graph below shows a cooling curve for a sample of gas that is uniformly cooled from ...
2
votes
1answer
59 views

How to find and use the Clausius-Clapeyron equation

I know how to get the equation from the Clapeyron equation but I have a question regarding a the integration along a phase boundary and a small step in the derivation that I will make clear when I ...
2
votes
1answer
43 views

Does the density of a liquid and gas phase of a substance(nitrogen or water) converge when reaching critical point

I know that the there is no difference in density in a liquid and a gas phase of a substance after the critical point. But I do want to know if this difference in density is more continuous or if it ...
2
votes
1answer
41 views

Phase rule and degrees of freedom

In the formation of 3-bromo-1-butene and 1-bromo-1-butene, from $\ce{HBr}$ and $\ce{C_4H_6}$, in a gas phase: $\ce{HBr + C_4H_6 \to 1BrC_4H_7}$ $\ce{HBr + C_4H_6 \to 3BrC_4H_7}$ the number of ...
4
votes
1answer
59 views

Phase diagrams (weird region)

On the left, there is a region for $\ce{MgO(ss)}$. I've been told such regions exist because stuff are not miscible. However, does that mean the composition axis on the bottom is a lie? Namely, ...
0
votes
2answers
25 views

What is the specific heat of copper through its phases?

Specific heat is the amount of heat required to change the temperature of 1 gram of a substance by 1 Celsius. For instance, the specific heat of water in the solid phase is 2.059 J/gC and 4.184 J/gC ...
0
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0answers
22 views

How can a melting and a freezing point of ice be the same [duplicate]

How can a freezing and a melting point of ice be the same ??
2
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3answers
241 views

Since the formation of diamond from Graphite is endothermic and the entropy decreases for this process, how is it possible to make diamond?

Surely G would always be positive and thus would make it impossible to make diamond. Clearly this is not the case. But how? Would an increase or decrease in temperature aid it's formation? I think a ...
2
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1answer
40 views

Are there attempts to investigate phase states at negative pressure?

Phase diagrams of various compounds and systems usually include only positive pressure. But I wonder whether it is possible to somehow investigate them under negative pressure? Are there materials ...
3
votes
1answer
85 views

Boundary lines in phase diagrams and the lever rule

My first question is: What exactly happens on a point situated on a line? Or on a point such as E in this figure? Does point E mean that the $\delta , \gamma + \delta , \delta + \epsilon , \gamma + ...
6
votes
1answer
200 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 ...
13
votes
2answers
720 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 ...
1
vote
2answers
60 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
2k 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
170 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
60 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
42 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
273 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
42 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
73 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 ...
1
vote
1answer
119 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
364 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
78 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
64 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
50 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
3k views

Why does water evaporate at room temperature?

When water temperature reaches $100^\circ \mathrm{C}$, 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, ...
5
votes
1answer
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 ...
3
votes
1answer
92 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 ...
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vote
2answers
198 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
233 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
308 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
354 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
56 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
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1answer
2k 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
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3answers
15k 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
824 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
44 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
556 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
697 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
118 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 ...
6
votes
1answer
302 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
596 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
6k 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 ...