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Questions tagged [phase]

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.

84
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8answers
42k 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't say ...
48
votes
2answers
7k views

What is the pH of ice?

The pH of pure liquid water depends on temperature. It is about pH = 7.0 at room temperature, pH = 6.1 at 100 °C, and pH = 7.5 at 0 °C. What happens to the pH (or to the ion product) of pure water ...
36
votes
6answers
394k views

Why does ice water get colder when salt is added?

It is well known that when you add salt to ice, the ice not only melts but will actually get colder. From chemistry books, I've learned that salt will lower the freezing point of water. But I’m a ...
29
votes
5answers
20k views

A glass of water with ice-cubes in it. Where's the water the coldest; at the top or bottom?

Suppose that I fill a glass with ice water. As the ice melts, it cools the water around it. Given that cold water is denser than hot water, I would presume that the cold water would sink to the ...
29
votes
2answers
5k views

What happens if you cool water in a container too small for it to freeze?

Freezing a full bottle of water tends to shatter the glass bottle. What if you used something tougher than glass, like diamond? What would happen if you kept dropping the temperature, but restrained ...
28
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4answers
1k 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 ...
22
votes
5answers
4k views

How does water evaporate completely when at room temperature?

If water evaporates at room temperature because a small percentage of the molecules have enough energy to escape into the air, then why does a kitchen counter with a small amount of water eventually ...
20
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6answers
2k views

Why does HCN boil at a higher temperature than NH3?

The boiling point of ammonia is −33 °C while that of $\ce{HCN}$ is 25 °C. In a recent AP (Advanced Placement) Chemistry test, a free response question asked why this is the case. Can someone shine ...
19
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1answer
4k views

Why can't helium be solidified at 'ordinary' pressures?

According to the UC Davis ChemWiki Chemistry of Helium, helium has a comparatively unusual property, specifically: Helium is the only element that cannot be solidified by lowering the temperature ...
17
votes
1answer
8k views

Molten vs Liquid

When I start studying electrochemistry,I learn the words molten and aqueous. I don't have a problem for aqueous but I'm a little bit confuse about molten. For me, molten means melt, which means ...
15
votes
2answers
36k 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,...
15
votes
4answers
88k views

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

I was working on something in school and came across the question: Why does the temperature not change much during a phase change? I'm really not sure why this happens in matter and I couldn't ...
15
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1answer
61k views

What is the melting point of diamond?

Textbooks and the online reference differ about this and there are more than two answers.
14
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6answers
5k views

Is there a cheap, safe liquid that evaporates EXOthermically around room temperature?

The heating and AC system in the building where I occasionally work, works like this (basically a thermostat): The administrators set some temperature that is maintained automatically. Say, in the ...
14
votes
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?
14
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3answers
22k views

Why are water droplets shaped like that?

With nothing to do, I stared at the droplets that get condensed on the glass panel of my window. Upon examination, these droplets appear to be in some sorta pattern. There are big droplets as well as ...
13
votes
2answers
5k views

Burns from boiling water and steam

Why is a burn to the skin caused by steam more serious than a burn caused by the same amount of boiling water at the same temperature? The temperature is the same, which implies that the kinetic ...
13
votes
5answers
23k views

Difference between state of matter and phase

What is the difference between state of matter and phase? This site said that: Phases are different from states of matter. The states of matter (e.g., liquid, solid, gas) are phases, but matter ...
13
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4answers
717 views

Room-conditions supercritical fluids?

Are there any reasonably obtainable supercritical fluids that I could, say, run my hand through? Wikipedia makes it sound like there are plenty of room-temperature ones, but no room-pressure fluids.
13
votes
1answer
190 views

How many particles are necessary to observe a well-defined state of matter?

The three ordinary states of matter $-$ solid, liquid, gas $-$ can usually be distinguished by a function of the strength of interparticular forces and distance. A shorter distance and a stronger ...
13
votes
2answers
3k views

What color is solid methane?

Is it blueish, perfect white or some other color? I am interested because some celestial bodies are said to be covered with methane ice.
12
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2answers
4k views

Why does ice crack when a drink is poured on it?

I think most people have experienced this, but while pouring a beverage over ice I noticed the ice cracked. Before After My initial thought was that because the beverage has an antifreeze property ...
12
votes
1answer
394 views

Jahn-Teller Metal : The new state of matter

Recently it came in the news that scientists have discovered a new state of matter called Jahn-Teller metal. I tried reading up on it but couldn't understand it clearly. Please explain in simple ...
10
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3answers
148k 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 melts at 0 °C?
10
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2answers
1k views

Can I pour a solution into another vessel with no air bubbles?

I have been trying to create a method to create a homogeneous agar solution. What are appropriate techniques to ensure homogeneous solidification of an agar-based aqueous solution? The new solution ...
10
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1answer
2k views

Why must both the critical temperature and pressure be exceeded to achieve the supercritical phase?

The characteristics and properties of supercritical fluids and the associated vapor-liquid critical point are well established. One thing that I've always been curious about, though: what is the ...
10
votes
1answer
5k views

What is melting? Which bonds do we break to melt something?

To melt diamond, we have to break the covalent bonds, which we can consider 'intermolecular' because it is one giant molecule. To melt Methane, we have to break the van der Waals (intermolecular) ...
10
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3answers
26k views

Why does small value of van der Waals gas constant “b” ensure easier liquefication?

Larger value of b signifies that the size of the molecules is larger and hence the forces acting should become larger due to increased surface area.This should ensure easier liquefication. But my book ...
10
votes
1answer
196 views

Why is ice sticky between −20 to −8 degrees Celsius but not below −30 °C?

I was watching an Air crash investigation video where the cause of the plane crash was determined to be due to blockage of fuel pipes by ice crystals (from the water in the jet fuel) which would have ...
9
votes
2answers
17k views

Why is active mass of a pure solid or liquid always taken as unity?

Active mass is defined as the molar concentration ie. number of Gram-moles per litre. My book then wrote Active mass of pure solid/liquid is always 1 . The book reasoned that Molar ...
9
votes
3answers
792 views

Is there a gas with metallic luster?

We know that both solids and liquids can exhibit metallic luster. I wonder whether there is a gas that when filling a transparent envelope (such as a glass tube) would make it appear with metallic ...
9
votes
1answer
3k views

Are there any gases more dense than liquids?

Inspired by Is there any type of liquid, other than mercury, that PTFE teflon is known to "float" to the surface in?, are there gases that are more dense than liquids? (So bubbles would sink ...
9
votes
1answer
110 views

Which elements tend to form the most phases?

Some combinations of two elements have very complicated binary phase diagrams across the weight% horizontal axis. Others are rather simple. Is this a function of only one or both of the elements ...
8
votes
2answers
9k views

What happens to the bleach after mopping?

At home, I clean the tiled floors by mopping with highly diluted bleach. After mopping, I let the floor dry. What happens to the acid in the bleach? Will it crystallize on the floor, stay there ...
8
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5answers
4k views

Why does the distance between molecules increase when the temperature is raised?

I have learnt that when we heat ice-like substances it changes to water and when I asked my teacher she said that the distance between molecules increases. When I thought about it a bit more a ...
8
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3answers
2k 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 ...
8
votes
1answer
461 views

Freezing point of oxygen-18 water

The freezing points of heavy water (3.8 °C) and tritiated water (4.49 °C) both seem to be well-known. I can't find anywhere that gives the freezing points of $\ce{H2^18O}$, $\ce{D2^18O}$, or $\ce{T2^...
8
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1answer
3k views

Significance of phase of atomic orbitals

I am learning about orbitals and bonding and antibonding MOs. So far, I know that when you combine s orbitals, you form both bonding and antibonding MOs- bonding when the wavefunctions are added in ...
8
votes
1answer
917 views

Open Database of Phase Diagrams?

Is there some kind of database that has information about phase diagrams of different substances? I'm mostly looking for phase diagrams of elements (silicon, iron, hydrogen, etc.) because I'm trying ...
7
votes
1answer
4k views

What phase of matter is shaving cream? [closed]

Our teacher asked us if shaving cream is a solid, liquid, or gas. She didn't quite know herself.
7
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1answer
2k 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 it ...
7
votes
1answer
3k views

change in state (sublimation and deposition)

I am slightly confused as to how I should think of changes in state (especially sublimation and deposition). Should I think of sublimation and deposition as skipping the liquid phase (fig 1) or should ...
7
votes
1answer
174 views

Why so few fluid phases?

Taking a look at the phase diagram of water By Cmglee - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=14939155 I see ice phases as much as up to 'Ice XI', but only one '...
7
votes
2answers
1k views

Is dew and water vapour the same?

Is it possible to say water vapour and dew is the same? I know that the water vapour is the gaseous phase of water. But what is the dew? I just wonder how can I categorised it. Is it the liquid or ...
7
votes
1answer
13k 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 ...
7
votes
1answer
5k views

Why does color of halogen deepens and the boiling point decreases down the group?

Why does the color of the halogens deepens as we go down the group? also why there is a change in physical state of halogens down the group? \begin{array}{c|c} \mathbf{Gas} & \mathbf{Color} \\\...
7
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3answers
3k views

Is glass an amorphous solid or supercooled liquid?

I have been informed that glass is a super-cooled liquid and is also considered to be an amorphous solid. Can it be both and, if not, what category does it fall into?
7
votes
1answer
484 views

At the eutectic point, what is the effect on the melting point of adding impurities?

At the eutectic point, what is the effect on the melting point of adding impurities? Increase the melting point Decrease the melting point No effect on melting point I know adding ...
7
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0answers
330 views

Is helium-4 a liquid at zero temperature and zero pressure?

As far as I know, for all substances other than helium, if you extrapolate the solid-gas line on the phase diagram, it passes through the origin. That is, no matter how low the temperature is, you can ...
6
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3answers
2k views

Does naphthalene in moth balls really sublimate or does it evaporate?

The triple point of naphthalene is $\pu{-56 °C}, \pu{1.05 kPa}$ (which is much less than $\pu{1 atm}$). So how can a naphthalene ball sublimate at $\pu{1 atm}$, when considering that its melting point ...