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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Liquification of gas to liquid at critical temperature

The gas that liquifies first, when cooled from 500K to its critical temperature given in parenthesis is a) $\ce{CO2}$ (304.1 K) b) $\ce{NH3}$ (405.5 K) c) $\ce{O2}$ (154.3 K) d) $\ce{N2}$ (126.0 ...
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calculate volume change on solid-gas phase change? [on hold]

Is this volume change calculated chemically or physically, as the chemical constituents don't change. Yet they might, in the case of a dissociating compound, say, the non-stoichiometric methane ...
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1answer
59 views

How does ice melt?

I know that when water freezes, it forms a crystalline structure created by the hydrogen bonds between polar water molecules. Also, I know that during a phase change, the potential energy of the ...
3
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1answer
34 views

Sulphur in powdered form: what structure?

Quoting this paper: A variety of allotropic states of elementary sulfur have been identified. Solid crystalline sulfur exists either as rings of 6-12 sulfur atoms (cyclohexasulfur, $\ce{S6}$, ...
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Equilibrium saturation/depostion rate calculation

I found the Knudsen/Langmuir equation for calculating the sublimation rate of a solid. If I have a closed system, once the vapor reaches the saturation pressure, the solid will continue sublimating ...
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33 views

Does autoionization occur in steam?

It is well known that H2O spontaneously autoionizes to H+ and OH- when it is in liquid phase. I was wondering whether it does the same in gas phase, either to the same extent as in liquid phase or at ...
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n-Butane, isobutane and propane [closed]

This questions is related to the condensation of the three flammable gases above. We respond to illegal clandestine drug labs where the lab operators are putting butane cans inside the freezer to ...
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1answer
31 views

Why do we consider all gasses to be in one phase?

Why do we take the phase of all gases 1. If all gases exist in 1 phase then why do we say that some gases are heavier than air, some are light also we collects some gases in lab by air displacement ...
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140 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 ...
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50 views

overall energy and the boiling point

i need help with the fractional distillation method of a couple of substances at least more than two substances , just like air actually what am i looking for is that why do substances in air with a ...
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27 views

Are open system phase transitions physical equilibriums?

I have been told that phase transitions=physical equilibriums. How can phase transitions be physical equilibriums? For example, if you have liquid water going into gas phase, doesn't delta G have to ...
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108 views

At what temperature (in kelvin) are most of the elements on the periodic table liquids?

This question is out of pure curiosity. At what temperature are a majority of the elements on the periodic table in a liquid state/phase of matter? For the purpose of this question, assume the ...
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38 views

'Chemical' First-order Phase Change

First order phase changes occur when one local minima of the Gibbs Free Energy becomes deeper than another. Thus at 1 atm and 99 °C, the Gibbs Free Energy of liquid water is less than the Gibbs Free ...
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Conceptual Ice Water Equilibrium

We observe that when we apply pressure on an equilibrated ice—water system then more of ice melts. $$\ce{ice(more~volume) + heat <=> water (less~volume)}$$ If we increase pressure then volume ...
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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.
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31 views

Heat capacity during state change

I read that the heat capacity of water when it is at 100 °C or 0 °C is infinite because all the heat given to it will not be used to increase temperature but to change the state. I am unable to ...
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322 views

Why is CH4 a gas at room temperature but CH3Cl a liquid?

I cannot figure out a question on my review sheet. The full question is: Methane ($\ce{CH4}$) is a gas at room temperature but chloroform ($\ce{CH3Cl}$) is a liquid. Explain why changing just one ...
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2answers
32 views

Which phase is more efficient for temperature changes?

In the case of attempting to heat and cool down an object of different states, if you in some case managed to achieve the same temperature of a solid, liquid and gas what state would scientifically ...
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1answer
58 views

Why does water condense on grass and iron grills in cold weather?

In my book it is said that in cold weather fog appears. This fog is nothing but water droplets. After a hot day if the night is cold then the moister in air starts to condense. What I do not ...
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Describing evaporation without entropy — what about Helmholtz?

I have in mind a rigid, impervious, heat-insulating vessel containing a monatomic liquid and vacuum. The vessel has an insulating forcefield inside, exactly at the surface of the liquid. It can be ...
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65 views

Why is carbon dioxide gas used in soda?

Why is carbon dioxide used in soda? What makes it preferable to other gases for this purpose?
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48 views

Phase subscript for supercritical reagent?

When writing a chemical reaction, one can use subscripts to denote the phase of a reagent, e.g. $\rm SiO_{2\ (s)}$, $\rm H_2O_{(l)}$, $\rm F_{2\ (g)}$ or $\rm Na^+_{(aq)}$. However, I need to write a ...
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2answers
46 views

Why don't substances have a condensation point?

All substances have a freezing point at which they transition from a liquid to a solid. They all also have a melting point at which they transition from a solid to a liquid. However, as far as I can ...
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1answer
38 views

Kinetics of air evolving from water on heating

Is there a simple relationship describing the kinetics of air evolving from water on heating? For example, if I let water at room temperature and pressure saturate with air, it should have some ...
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Fluid Separation

I've been trying to find a way to prevent cornstarch and water from separating. If I'm right, emulsifiers are used to prevent fluid seperation with oils, but will an emulsifier fix my problem too? If ...
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High quality phase diagram for ethanol

I know the more general question has been asked here: Open Database of Phase Diagrams? And this has a link to slightly more specific question with more answers: Phase diagram for first 10 elements ...
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Determining Pressure of Sublimation of Iodine

The pressure of sublimation of iodine can theoretically be determined by considering the two hypothetical steps: the sublimation of iodine at 298 K, followed by an isothermal expansion of our ...
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841 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 ...
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77 views

What equipment to use to make liquid oxygen?

I'd like to do some experiments with liquid oxygen but as a first step I'll have to make some. Unfortunately I don't have any experience designing cryogenic experiments. I'm thinking I'll cool gaseous ...
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Hydrogen phase transition

A sample of hydrogen at a pressure of 7.10×10-2 atm and a temperature of 26.4 K is compressed at constant temperature to a pressure of 18.5 Which of the following are true? 1. One or more phase ...
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43 views

Can you call a table frozen?

Someone has argued that the table sitting in front of us is 'frozen'. I do agree that the table has a freezing point. The table has a melting point, but that is beyond the ignition point and the ...
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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 ...
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2answers
375 views

Sublimation of Iodine

Why does iodine sublime? I have researched it myself and I have got the same answer; it sublimes because it directly converts from solid to gas. But why don't bromine or chlorine also sublime?
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Ice under very high pressure phase transitions [duplicate]

If you put a piece of ice into a very high pressure chamber and increase the pressure, I can understand how the ice turns to a water state. But what happens after that? Does the pressure push the ...
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1answer
110 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 ...
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What is the state of the oxygen free radical in the following reaction?

$$\ce{O2(g) ->[h\nu][\nu\,<\,240~nm]2O^{.}(?)}$$ Oxygen is split by UV light below 240 nm to form oxygen radicals, which then go on to react with oxygen molecules to form ozone. Firstly, is ...
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1answer
91 views

How long does it take to change states of matter?

I'm interested to know how long it takes to change states of matter and why it takes the time that it does. For example, what is the very quickest that we could freeze a packet of chicken breasts? ...
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2answers
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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 ...
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1answer
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Properties of plasmas

In chemistry one can recognize that the four states of matter are solid, liquid, gas and plasma. The first is rigid, and has a definite shape and volume. The second doesn't have a shape, and assumes ...
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Making Liquid CO2

I recently saw a video on making liquid $\ce{CO2}$: https://www.youtube.com/watch?v=8AN_XMcD3yI Basically we seal some dry ice in a container. As the dry ice sublimates the pressure inside the ...
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What phase of matter is salt when dissolved in water? [duplicate]

Being an ionic solid, salt is very susceptible to being torn apart by the polar molecules of water. Inside the water, salt exists as sodium and chlorine anions; but what state of matter is it in? My ...
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Generating Precipitation Diagrams with CompuTherm Pandat

I am trying to develop precipitation diagrams for an Ag-Cu-Sn alloy to figure out the kinetics involved using the CompuTherm Pandat Software (Demo Version). The precipitation diagrams need the ...
3
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1answer
232 views

Contact explosion of nitrogen triiodide

Nitrogen triiodide, on slightest physical contact, explodes to evolve dense purple fumes of iodine. Why does this phenomenon occur? video link - https://www.youtube.com/watch?v=2KlAf936E90
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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 ...
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1answer
49 views

Solidification of sodium polyacrylate

Sodium polyacrylate is a white powder with a characteristic odor. But when we add water to this powder, instead of forming a aqueous solution , it instantaneously solidifies and forms more amount of ...
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421 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.
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195 views

Color of halogens

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} ...
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2answers
726 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 ...
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644 views

What is the difference between an amorphous solid and glass?

They are both formed when a liquid is supercooled rapidly, no free energy, and they both have irregular structures. What defines a glass other than how it is amorphous, transparent, and has a glass ...
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The effect of air pressure on the “melting point”?

a) No effect b) The melting point increases when the air pressure increases c) The melting point decreases When the air pressure increases The boiling point has inverse relation with ...