Question About Steam

[Mintaka]

When I watch clouds of steam after a bath or shower, what exactly is each droplet of steam? When water gets hot, is it the actual molecules themselves which escape the surface tension of the water and is steam made up of water molecules? If not, roughly how many water molceules would these tiny steam particles contain? Is it possible to actually "see" a water molecule with an electron microscope?

[Qfwfq]

First, we can distinguish between clear, "dry" water vapour and white, "wet" steam. It is not an actual mistake to use the word steam for either of these things, but it is well to understand that there are both of them.

 

When water gets hot, is it the actual molecules themselves which escape the surface tension of the water

Yes, when water evaporates, it means individual molecules are leaving the surface and mixing into the air. Boil a kettle and carefully observe the steam exiting the spout; if the kettle is fully hot you don't see anything right at the opening. It becomes white as it cools down in the air.

 

and is steam made up of water molecules?

Water vapour is, but white steam contains many tiny droplets of liquid water. The number of water molceules each droplet contains is huge, getting on for a billion billion according to its size.

 

Is it possible to actually "see" a water molecule with an electron microscope?

No.

[CraigD]

Good questions!

 

Qfwfq beat me to answers, and while I agree with him, since I spent the time to write them, I’ll post mine here and now.

 

When I watch clouds of steam after a bath or shower, what exactly is each droplet of steam? When water gets hot, is it the actual molecules themselves which escape the surface tension of the water and is steam made up of water molecules?

Steam you can see consists of fairly large water droplets, about 0.00001 m diameter. It’s also cool (under 100 C) a good thing, as we don’t want to be burned to death in our showers!

 

The word “steam”, though, has several meanings. “Live” steam does consist of a “pure” gas of separate water molecules. It’s invisible and anywhere from hot (100 C) to terribly hot (up to about 2500 C).

 

Live/pure water gas eventually cools and begins to form droplets. When the droplets become big enough, they becomes visible as “ordinary” steam.

 

The wikipedia article steam described this decently.

 

If not, roughly how many water molceules would these tiny steam particles contain?

Taking the 0.00001 m diameter above and the molecular mass of water (18 AMU = 3.0e-26 kg), we can calculate that the droplet has a volume of about 5.2e-16 m³, a mass of about 5.2e-13 kg, so consists of about 1.7e13 (170 trillion, as we say in the US) molecules.

 

Is it possible to actually "see" a water molecule with an electron microscope?

In principle, TEMs can image features as small as individual atom. Direct “feeler” microscopes like STMs and AFMs are even better suited for this – most of the published images of individual atoms (Like the famous 1990 image of “IBM” spelled in individual xenon atoms) are produced by them.

 

The basic requirement of microscopy on this scale is that the sample hold very still, which means cooling it to a very low temperature, so any imaged water molecules would have to be in ice form. Liquid or gas water molecules simply move around to fast and randomly to “get a lock on” with any present day imaging technology, I think.

[Mintaka]

Hey thank you both for these excellent replies to my question about steam. I was in England for the New Year holidays and not being ignorant by not replying.

 

The more I look at water the more fascinated I am by it. I had no idea there were so many molecules in a droplet of steam. It's incredible. Are you saying that with these microscopes you speak of, we CAN actually see a water molecule?

 

 

 

Good questions!

 

Qfwfq beat me to answers, and while I agree with him, since I spent the time to write them, I’ll post mine here and now.

 

 

Steam you can see consists of fairly large water droplets, about 0.00001 m diameter. It’s also cool (under 100 C) a good thing, as we don’t want to be burned to death in our showers!

 

The word “steam”, though, has several meanings. “Live” steam does consist of a “pure” gas of separate water molecules. It’s invisible and anywhere from hot (100 C) to terribly hot (up to about 2500 C).

 

Live/pure water gas eventually cools and begins to form droplets. When the droplets become big enough, they becomes visible as “ordinary” steam.

 

The wikipedia article steam described this decently.

 

 

Taking the 0.00001 m diameter above and the molecular mass of water (18 AMU = 3.0e-26 kg), we can calculate that the droplet has a volume of about 5.2e-16 m³, a mass of about 5.2e-13 kg, so consists of about 1.7e13 (170 trillion, as we say in the US) molecules.

 

 

In principle, TEMs can image features as small as individual atom. Direct “feeler” microscopes like STMs and AFMs are even better suited for this – most of the published images of individual atoms (Like the famous 1990 image of “IBM” spelled in individual xenon atoms) are produced by them.

 

The basic requirement of microscopy on this scale is that the sample hold very still, which means cooling it to a very low temperature, so any imaged water molecules would have to be in ice form. Liquid or gas water molecules simply move around to fast and randomly to “get a lock on” with any present day imaging technology, I think.

[Qfwfq]

Are you saying that with these microscopes you speak of, we CAN actually see a water molecule?

We can't "actually see" it, no. The type of instrument Craig talks about simply has a very fine mechanism and it traces out the shape of the surface or, at least, of the surface distribution of electron density, and it can do this at a geometric resolution below the atomic scale. What you actually see is a plotted graph of the surface shape, or some other rendering of it.

 

This is very unlike microscopes which use the optics of electrons and which, reaching those scales, would inherently tend to blow the material apart.

[Mintaka]

We can't "actually see" it, no. The type of instrument Craig talks about simply has a very fine mechanism and it traces out the shape of the surface or, at least, of the surface distribution of electron density, and it can do this at a geometric resolution below the atomic scale. What you actually see is a plotted graph of the surface shape, or some other rendering of it.

 

This is very unlike microscopes which use the optics of electrons and which, reaching those scales, would inherently tend to blow the material apart.

 

 

So, when we view things at this scale, it is the electrons which we are important, which are being viewed? Forgive me, I thought that electrons were particles which orbited the atoms themselves, and therefore much smaller than molecules? What do you mean by electrons being 'blown apart' when viewed at those scales? Does an electron microscope physically affect or interfere with the materials it is viewing?

 

If we can only see a 'plotted graph' at the atomic scale, and not a visual rendering of the particles, does this simply mean that our optical instruments (lenses etc) are not powerfuil or big enough to see them? Does increasing the lens diameter increase their power, as is the case with 'far'seeing' telescopes ( Hubble etc)? Is optical technology developing and do you think it is likely that one day we will be able to visually "see" atomic & subatomic particles?

 

I find visual scale-comparisons really useful. Do you happen to know of any 'scale' comparison which might help us to get some concrete visual idea of the size of a water molecule? Im asking this because the idea that a glass of water contains more water molecules than there are grains of sand on the earth mind-blowing and hard to grasp.

 

For example, there is the one that says if the earth was the size of a grape of 1 cm diameter, the sun would be a sphere of 1.5 m diameter standing at 150m distance from the grape etc etc.....so...along similar lines, if a grain of sand (or a human egg) were the size of a ( football for example..) how big would the water molecule be? I don't expect you to start making detailed calculations, just wondering if you have heard off-hand of such a scale model which would help us to wrap our minds around such mind-boggling things.

 

It would have been great at school if my teachers had not presented physics as such a dry dull subject and called it 'science'...they would have got me interested for ever at the age of 10 if they had called it 'magic', because that's really what it is.

[HydrogenBond]

To see the water molecule with an instrument often means the instrument will upset the actual shape. To get around that, we use mathematical equations, called wave functions, to generate an image on the computer. For example, below is an image of a water molecule using an equation called the Restricted Hartree-Fock wave function (RHF) using the 6-31G** basis set.

 

[Qfwfq]

So, when we view things at this scale, it is the electrons which we are important, which are being viewed? Forgive me, I thought that electrons were particles which orbited the atoms themselves, and therefore much smaller than molecules? What do you mean by electrons being 'blown apart' when viewed at those scales? Does an electron microscope physically affect or interfere with the materials it is viewing?

Actually, I said it would tend to blow the material apart, not the single electron, but the whole thing is very complicated. What actually happens with high energy electrons is that most of them go straight through (or nearly straight) but the few that would be more useful for the workings of a microscope give a whopping nudge to some particle. The trouble is that if they don't each have a high energy:

If we can only see a 'plotted graph' at the atomic scale, and not a visual rendering of the particles, does this simply mean that our optical instruments (lenses etc) are not powerfuil or big enough to see them? Does increasing the lens diameter increase their power, as is the case with 'far'seeing' telescopes ( Hubble etc)? Is optical technology developing and do you think it is likely that one day we will be able to visually "see" atomic & subatomic particles?

The wavelength associated with the light or the electrons is an inherent limitation and it depends on the energy. To see small things you need a short wave and the energy of each particle is high.

 

For example, there is the one that says if the earth was the size of a grape of 1 cm diameter, the sun would be a sphere of 1.5 m diameter standing at 150m distance from the grape etc etc.....so...along similar lines, if a grain of sand (or a human egg) were the size of a ( football for example..) how big would the water molecule be?

Suppose hydrogen atoms were neat little balls and you could line them up side by side; at their actual size, a row of ten million of them could fit into a millimetre. So, if you scale things up till atoms are a millimetre across (and a wat3er molecule is not much bigger), then sizes of typical grains of sand would be comparable to the actual size of Earth.

[Mintaka]

Actually, I said it would tend to blow the material apart, not the single electron, but the whole thing is very complicated. What actually happens with high energy electrons is that most of them go straight through (or nearly straight) but the few that would be more useful for the workings of a microscope give a whopping nudge to some particle. The trouble is that if they don't each have a high energy:The wavelength associated with the light or the electrons is an inherent limitation and it depends on the energy. To see small things you need a short wave and the energy of each particle is high.

 

Suppose hydrogen atoms were neat little balls and you could line them up side by side; at their actual size, a row of ten million of them could fit into a millimetre. So, if you scale things up till atoms are a millimetre across (and a wat3er molecule is not much bigger), then sizes of typical grains of sand would be comparable to the actual size of Earth.

 

 

you've just blown my mind again. A hydrogen atom scaled up tp 1 mm diameter would mean the grain of sand would be similar in size to the earth? It's much bigger than I expected. Thank you.

[Qfwfq]

Garsh, looks like I screwed up here that day, confusing millions with billions on the fly. Or maybe I confused metres and millimetres. :doh: Scaling a grain of sand up ten million times, it would become comparable to a big mountain, lets say.

[Mintaka]

Garsh, looks like I screwed up here that day, confusing millions with billions on the fly. Or maybe I confused metres and millimetres. :doh: Scaling a grain of sand up ten million times, it would become comparable to a big mountain, lets say.

 

thanks, we all have off-days ;-)