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NathanUT

Are Steam & Water Vapor Visible?

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OK, I feel confident I know the answer to this, but my colleague refuses to accept my explanation. It's silly since the answer to this is not all that relevant, but as a teacher, I want to be sure I am not teaching concepts that are technically incorrect...

 

That being said, I believe water vapor & steam (steam is a common type of vapor, right?) are totally invisible. The argument/common misconception is that you can see steam in the form of the little white cloud rising above a tea kettle or steam vacuum. It is my understanding though, that the little white cloud is just that... a cloud. And a cloud is water in liquid form that is coming together & condensing, but not yet dense enough to fall. It is my understanding that when you boil water in a tea kettle, the vapor is invisible. However, as it moves farther away from the source of heat, the vapor starts to cool and condense into liquid drops. Those liquid drops are what you see, NOT water vapor. Can anyone confirm? This makes perfect sense to me, but I can totally see why there is such a misconception on this topic. Steam cleaners put out a white cloud of steam, and steam is water vapor... so water vapor must be visible

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You're right. If you want authority, here's the Oxford English Dictionary on the subject:

 

In popular language, applied to the visible vapour which floats in the air in the form of a white cloud or mist, and which consists of minute globules or vesicles of liquid water suspended in a mixture of gaseous water and air. [...] In modern scientific and technical language, applied only to water in the form of an invisible gas.

 

It's the difference between scientific and colloquial usage that makes it controversial.

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You're right. If you want authority, here's the Oxford English Dictionary on the subject:

 

 

 

It's the difference between scientific and colloquial usage that makes it controversial.

 

Sweet! I think that will settle it. Thanks for the response.

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From what I remember from physics lessons at school if you look carefully at steam issuing from a boiling kettle the steam will seem to appear to form a little distance away from the spout. Therefore it cannot be seen until it starts to condense. That was in the days when kettles were boiled on a gas ring and could be kept boiling for the observation. These days with electric kettles which automatically shut off it's not so easy! (Not to mention 'elf an safety)

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From what I remember from physics lessons at school if you look carefully at steam issuing from a boiling kettle the steam will seem to appear to form a little distance away from the spout. Therefore it cannot be seen until it starts to condense. That was in the days when kettles were boiled on a gas ring and could be kept boiling for the observation. These days with electric kettles which automatically shut off it's not so easy! (Not to mention 'elf an safety)

 

however, steam has a different refractive index to air so it'd be visible by the way objects behind it would appear distorted. transparent, yes, invisible, i'd say not.

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however, steam has a different refractive index to air so it'd be visible by the way objects behind it would appear distorted. transparent, yes, invisible, i'd say not.

 

I think at that level it's a matter of semantics of what invisible is. The air has a refractive index different from a vacuum, too, but for normal incidence of any refractive material there is no distortion. Also, air will scatter light according to frequency, so you could detect the presence of air by seeing if any blue light is scattered perpendicular to the light path; we see a blue sky, but we consider air to be invisible, don't we?

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Steam is most definitely invisible (naked to the human eye). It only gives the appearance of being visible some distance from the source where the steam actually has the potential to condense and form liquid visible droplets (water) again.

 

Your colleagues are definitely misinformed if they think otherwise.

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yes u r right NathanUT, i also believe in the hypothesis u made from some time..........the visibility of vapors, i think can also depend on the size of vapours......bt i dont know that what size or in what range the size of water vapors or other liquid vapors have?.......could u plz post some data regarding the size of common liquid vapours......so that we can just see that they can be seen by naked eye?...................i think that the size will be far away from the range of our eyes ability to see them.......in my opinion.......

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!

Moderator Note

 

@sidhu,

 

Please note that the thread is already 2 years old. Some of the people responding to the thread may no longer be active. NathanUT has not logged in to this forum since May 4th 2011.

 

It is not against the rules to respond to an old thread like this. But you should realize that you are only doing it for your own entertainment, not to help the person who opened the thread.

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yes u r right NathanUT, i also believe in the hypothesis u made from some time..........the visibility of vapors, i think can also depend on the size of vapours......bt i dont know that what size or in what range the size of water vapors or other liquid vapors have?.......could u plz post some data regarding the size of common liquid vapours......so that we can just see that they can be seen by naked eye?...................i think that the size will be far away from the range of our eyes ability to see them.......in my opinion.......

 

There are no atoms or molecules visible to the naked eye. If you can see it, it will because many of the molecules have coalesced.

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To throw a wrench into the explanation, it depends on whether the steam is saturated or superheated. I can state with 100% certainty that you cannot see the steam from a 1200 psi boiler on a US Navy ship because it is superheated. When the main steam line gets a break in it, the safest way of finding it is by running a broom along the line until it either bursts into flame or is sheared off. You will not see the leak by looking with your eyes.

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There are no atoms or molecules visible to the naked eye. If you can see it, it will because many of the molecules have coalesced.

Actually, there are plenty of molecules visible to the naked eye.

Here's a fairly well known one.

http://en.wikipedia.org/wiki/Cullinan_Diamond

And here's a more accessible one.

http://en.wikipedia.org/wiki/File:Quartz_synthese.jpg

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Molecules are typically though of as the smallest unit of the substance. Quartz, for example, is given as SiO2 so the quartz crystal you can see is many, many molecules. Similar with diamond, or any other crystal structure.

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Molecules are neutral collections of atoms held together by chemical bonds.

"A molecule /ˈmɒlɪkjuːl/ is an electrically neutral group of two or more atoms held together by chemical bonds." from wiki

 

The bonds occur throughout a diamond.

All the bonds are the same, and all the atoms are held to eachother by chains of chemical bonds.

 

A diamond is a single molecule, even if it's big enough to hurt if you drop it on your foot.

 

Molecules vary depending on how the atoms are linked together. The simplest unit of diamond is a carbon atom, and yet the same is true of graphite.

So, if the molecule is the simplest unit then graphite and diamond, having the same simplest unit, must be the same sort of molecule.

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Molecules are neutral collections of atoms held together by chemical bonds.

"A [/size]molecule [/size]/ˈmɒlɪkjuːl/[/size] is an electrically neutral group of two or more [/size]atoms held together by [/size]chemical bonds." from wiki[/size]

 

The bonds occur throughout a diamond.

All the bonds are the same, and all the atoms are held to eachother by chains of chemical bonds.

 

A diamond is a single molecule, even if it's big enough to hurt if you drop it on your foot.

 

Molecules vary depending on how the atoms are linked together. The simplest unit of diamond is a carbon atom, and yet the same is true of graphite.

So, if the molecule is the simplest unit then graphite and diamond, having the same simplest unit, must be the same sort of molecule.

 

Interesting that the wikipedia article doesn't list diamond as the largest molecule, and says the largest one on record is around 100 nm.

 

The structure of graphite and diamond differ. Molecules typically refer to the smallest repeating structure. Using your interpretation, a block of ice, or salt, would have to be considered a molecule. In fact, most solids would. However, we don't do that. When one refers to molecular formulas, one typically does not have to ask how big the sample is, because that defeats the purpose behind the concept.

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"Interesting that the wikipedia article doesn't list diamond as the largest molecule, and says the largest one on record is around 100 nm."

Interesting that it fails to notice that a typical DNA molecule is nearer a metre than 100nm.

 

 

"Using your interpretation, a block of ice, or salt, would have to be considered a molecule. "

No, blocks of ice are held together by hydrogen bonds, not covalent ones like diamond or quartz.

Salt crystals are held together by electrostatic forces between ions.

That's why I chose diamond and quartz.

 

I don't see anyone asking for the molecular formula of diamond, so that's irrelevant. However the molecular formulae of polymers are often given as things like (C2F4)n and you could call diamond Cn if you really wanted a molecular formula.

 

A diamond is a single molecule: it's not a very controversial point of view

http://www.physicsforums.com/showthread.php?t=171339

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Molecules are neutral collections of atoms held together by chemical bonds.

 

What with hydrogen bond? smile.png

Will we count it as "chemical bond" or not?

(it's mentioned in http://en.wikipedia.org/wiki/Chemical_bond )

If we count it as well, the largest "molecule" on Earth is ocean.

 

DNA molecule is using hydrogen bonds extensively.

Edited by Sensei

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As far as know, a hydrogen bond is defined as a bond between molecules (or in certain cases between two groups of the same molecule). Hydrogen bonds do not turn our oceans into one giant molecule.

 

A DNA molecule has many hydrogen bonds. But it has covalent bonds that are the reason we call it a molecule.

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