temp of steam

Factual Questions
21

Ok… Fire is the quintecential oxidation of a substance. Take a log, burn it in a controlled environment and it will weigh more than when you started burning it. This is due to Oxidation or the addition of oxygen molecules to the structure molecule. We’re talking basic chemistry 101.

Plasma is the dis-orientation of atoms in a steady state (debatable). While fire rearanges molecular structure, plasma (high heat) rearanges molecules and atoms themselves. “Fire” could relate to all of these, but I’d hold it to the norms of what happens on Earth for now; you never know what some “Joe” will think up next.

22

(cut and pasted from the Houghton Mifflin Co. message board)
So this guy is wrong then. Right?

23

You guys forgot phlogiston. It explains everything.

24

Back to the original topic …

It seems unlikely that the steam above an open pot is much hotter than 212F. That’s because the steam is being cooled both by the 212F water below it, and by the (much cooler) air above it. So at steady-state, the steam might be a little hotter, but not much. I’m also assuming that the air pressure inside and outside the pot is the same; i.e., that it is open at the top.

This hypothesis is based on a year of college-level thermodynamics, so it’s not entirely a WAG.

The Cat In The Hat

25

A plasma is a gas that is so energetic the particles knock electrons off of each other and the gas itself therefore conducts electricity. Or as it was much more eloquently put above, an “ionized gas.”

Plasma is made by combining fire and air, and a few more gin and tonics, please.

Know those cute little teapots that whisle when they come to a boil? That clear part just at the tip of the whisle is steam while the cloudy water vapor is… water vapor. Since the whistle is made by overpressure within the pot, it is safe to assume that that little clear jet is much hotter than 212 F @ s.l. Once it vaporizes, it is back to 212 and below.

26

I think you guys are somewhat misinterpreting B_Line’s question. I agree in essence with Squid; if a sufficiently powerful heat source is applied to the bottom of the container, it would become hot enough to ‘flash’ the water molecules to steam at a temperature somewhat hotter than 212 degrees. Squid said to disregard the effect of overcoming the water pressure – I say this is probably the decisive factor that permits the steam to reach ~ 90+ over ‘normal’ boiling point just above the surface of the water.

As for fire being plasma – which is hardly ‘science fiction’, Sofa King, where’d that come from? – wellllll, it’s stretching a point. ‘Fire’ as we might conventionally think of it coming from the burner of a gas stove may contain some ions, but it’s certainly not predominately composed of ions. I think it would be more scientifically accurate to say ‘fire contains individual plasma molecules/atoms’, but the most reliable test (to me) would be, can you contain the gases in question (or at least control their motion) with a magnetic field?

And Coach, just FYI, the word you meant to use is ‘quintessential’.

27

Yes, slightly perhaps. But the important thing to remember here is it can’t heat the steam to a temperature hotter than the pot itself! There is no way that that pot (on a normal stove at least) is gonna get up to 300 F, while it is full of 212 F water!

28

Re fire being a plasma–

After reading some of those articles, I am going to say that I guess fire can be called a plasma. Multiple folks there claim that flame has a noted increase in electrical conductivity. This is the first time that I have heard of a flame described as such. It is probably much less ionized than your typical plasma tho.

29

Yes, slightly perhaps. But the important thing to remember here is it can’t heat the steam to a temperature hotter than the pot itself! There is no way that that pot (on a normal stove at least) is gonna get up to 300 F, while it is full of 212 F water! --Undead Dude

Agreed, but I believe that averaging the temperature of the pot bottom is where you introduce the error – e.g., on the spot of the bottom where a gas flame’s hottest point (what’s the name for that, BTW?) might be adjusted to be, that point will alternately (millisecond to millisecond, I suppose) vary from hundreds of degrees to ~212 (as the bubbles form and detach, allowing more water to rush in and reheat).

30

I just conducted a little experiment in the kitchen. I heated a kettle of water to boiling, inserted a food grade thermometer through the whistle hole, and held it for quite a while. The temperature stabilized at 100 C. I was careful to keep the tip of the thermometer out of the water.

Let’s talk about physics now:

To boil water, you must supply sufficient energy to raise the temperature of the water to about 100 C. Now, more energy has to be provided to push the water from liquid to gas. This is the heat of vaporization. Numerically it’s 539.55 cal/gm. That’s a considerable amount of energy.

Now, on to condensation, the heat of vaporization must be given up before water vapor can condense. The vapor condenses to 100C water, with the extra energy being absorbed by you, the heatsink.
The burn you receive from sticking your hand in steam comes not from the temperature of the gas, but the energy given up in the state transition from gas to liquid. Set your oven to 100 C and stick your hand in. I bet you could keep it there for quite some time.

So, since the vapor is 100C with loads of energy available with a state transition, why did the thermometer I used in my experiment not show a temperature above 100C–because the actual physical thermometer was coated with water at equilibrium with the vapor. Suppose a molecule of water condensed on the thermometer. It would deposit its energy into the water coating. You could consider it as raising the temperature above 100C. With this new energy, a water molecule could escape the water coating and join the vapor. The physical thermometer also conducts heat out of the kettle, into my hand. The thermometer drops below 100C, some vapor condenses, and raise the temperature back to 100C.

Ok finally, in terms of energy absorbed per some unit of time, what worse, bathing in 100C water vapor, or 100C water? Back to the stove! From a number of trials, I found that it took on average 12 seconds to raise the thermometer’s temperature from 10C to 100C when submerged in the boiling water and about 14 seconds on average for vapor only measurements. I performed four trials of each, interleaving the tests. I would have used a piece on meat on the thermometer to simulate my flesh, but I fresh out of the stuff.

Now as I mentioned in another topic, I am an expert magnet. An expert on the topic will now appear, call me an idiot, and give you another story.

31

OK, OK. Undead Dude I concede your point…sorta. Being a “scientist” I decided to rely on empirical evidence. So, while you guys have been arguing, I did an experiment. I put 1 liter of water in a 3 liter erl. flask and started heating it. The temp of the steam (as measured by a temp probe suspended into the steam) never exceeded 212 deg. F; UNTIL almost all of the water was gone. The temp then rose dramatically and leveled off to around 250 deg F. I blame this on my heat source. I used a rather small hot plate. So I’ll stand by my statement that if you impart enough energy to flash the water into steam it can become superheated. However, practically speaking, the steam is around 212 deg F.

“If you stick your finger in a pie, whatever is in the pie will be on your finger, and whatever is on your finger will be in the pie…unless you wear a rubber glove”----some demented old lady

32

I must say that I am impressed with the initiative of the empiricists! Who wants to volunteer to collect eveidence for relativity? :wink:

The reason that you don’t get burned quickly if you stick your hand into a 100 C oven that contains only air, is because air is of a very low density, and has little ability to transfer energy to you.

I really think that the role of vaporization heat is overblown a lot in this thread. Certainly it is there. Certainly it is important. But I don’t think it is nearly as important as has been frequently suggested.

It may very well be the case then when you stick your hand in 100C steam that most of the energy imparted to your hand will be the heat of vaporization. That is to say, the energy to convert the steam to water might be (I haven’t actually tried to calculate this yet) more than the energy to to reduce the condensed water droplets from 100C to skin temperature. However, I bet that a lot more energy would be transferred if your oven was filled with 95 C water.

Well, no the reason that the thermometer did not show a temperature above 100C is because the vapor/steam is 100C! Heat transfer cannot occur from a colder object to a warmer object. That is fundamental to the concept of temperature. Once the thermometer reaches 100C it no longer causes condensation.

Of course condensation sets in very quickly when the steam hits cool air, so much of what would contact your thermometer would have already condensed beforehand. Unfortunately a definitive experiment of this nature would be rather hard to do without special equipment. A good test would involve putting a thermometer into a sealed container of dry steam, and comparing that to a thermometer put into a sealed container of water at the same temp.

33

I’m with you here. A lot of the fun of science is considering the impractical, yet non-impossible. :slight_smile:

34

You really think the variation would be that high? This is a judgement call, but I think that with a pot made of a normal material, a hot spot would become a haven for nucleation (thus cooling the pot) long before the hot spot would get very far above 212F. Keep in mind that most of the cooling of the pot is taking place while the bubble is expanding (as this is when vaporization occurs).

35

Ok Undead, riddle me this:

If 1 gram of water vapor condenses on you, how much energy is absorbed by you?

63 calories because the water is 100C to start and you ar 37C to start.

539 calories because of the state transition.

That’s almost a ten-fold difference.
About air density. Dry air is more dense than steam. The barametric pressure is greater on cold humid days than it is on hot dry days.

Look, I’m not saying that immersion in boiling water is less dangerous that immersion in steam, I’m saying that with a sufficient flux of steam they’re close to equivalent.

Also, my equilibrium description is correct. Molecules don’t know the temperature of anything. They land, they leave. That’s how it is.

Sorry, got to go have surgery now. Bye

36

Well, that’s clear then that most of the heat from steam would come from the heat of vaporization . I guess my attacks on heat of vaporization were really kinda irrelevant to what you were saying.

And I would agree with that. It goes along with what I said about circumstance, rather than heat of vaporization.

Well, no. You can’t discuss temperature and vaporization and then turn around and tie that to the nature of individual molecules. That crosses the line from thermodynamics to quantum mechanics. Concepts like vaporization and temperature are meaningless outside of the context of large agregates.

Let’s put it this way. When your thermometer reaches 100C, an equilibrium between vaporization and condensation will be reached resulting no net increase in condensation. That is what I meant by “no longer causes condensation”.

37

Well done UD, I see no error in your logic, reasoning, and most importantly facts. One can pretend that a couple of molecules over a hot nucleation site at the bottom of a pan (contradicting the fact you expressed saying temperature is a non-issue when dealing at a molecular level), but it doesn’t relate to the question at hand. The very hot steam at those points will transfer all the excess heat into the water as it rises to the surface. So even if you could measure heat at a molecular level, it wouldn’t propose a possible situation where 300F steam at the surface of the pot can exist.

38

Sorry to change the subject again, but I had to put my 2 cents worth in on the subject of flame:

When you see a red, orange, yellow, or white flame, what you’re seeing is soot particles boiling off the flame source, being briefly incandescent before being oxidized. A flame with complete combustion produces only that blue glow like you get in gas stoves. An ordinary flame like a candle flame is actually inefficient; it has to “smolder” enough for you to see a luminescent flame.

You can prove this, if you want to spend a few bucks: go out and buy a gas mantle, the kind that go in camping lanterns. Follow the directions on the box for priming it. Then presuming you have a gas stove, light the burner and put the gas mantle on it.

You will get a blindingly bright light as the heat of the flame makes the mantle incandescent. The mantle will probably quickly burn out, since they weren’t intended to take that much punishment, but it demonstates the principle.

39

Ya know, Mr Thin Line, now that I look back at your previous post, I see that you were already talking about the equilibrium of water and vapor. Geez. Why didn’t I see that? I guess I was just rushing to the issue of heat transfer. So it looks like although I reacted to much of what you said, there really isn’t anything that I should have been disagreeing with.

40

How to enjoy steam up to 212 deg F in the sauna: http://www.sauna.fi/pages/recomm.htm

I seem to remember sauna thermometers going to 120 deg C, but most people leave the room at 90 deg C. The steam is generated by hot rocks, so not much to do with the boliling kettle problem.

Have you guys applied the ideal gas law (PxV=nRT) to figure out what pressure is needed for 300F? You deal with deg Kelvin!