I have heard that the temperature of steam over boiling water can reach 300 degrees yet boiling water can not reach above 212 degrees. Where does this extra energy come from?
212 degrees causes water to boil, at least at sea level, above or below has different temps to do so.
Going much above 212 causes the water to boil rapidly and then eventually it turns to steam. Steam is definitely hotter than the boiling water, but I am not sure to what temp it can become. But if you hold a solid object like a pan lid over the steam it will collect and eventually cool to the point of the boiling water and then drop back down into the pan.
Tip: Do not hold your arm or anything else above a steaming pot, it will burn you.
Jeffery
The temperature of steam depends on how much pressure the steam is under. The steam in high pressure steam lines regularly exceeds 500 degrees.
Great for making ships go!!
H2O, like all basic compounds and elements, has at least three phases: ice, water, and steam. Then there’s plasma, but we’re talking science, not science fiction, right? All are related to temperature, pressure, and volume.
Science has known for years that the elements can be combined in different ways to form different compuonds. Earth combined with water, for example, makes mud. Similarly, water combined with air makes club soda. Water, air, and fire makes a gin and tonic. Hmm. I think I’m thirsty.
Well, steam can be many temperatures-- at normal sea-level air pressure, it can’t be any colder than 212 F, but it can be much hotter.
However, if you have a pot of boiling water sitting on your stove, you are not going to find any 300 F steam above it. Actually, you will briefly find 212 F steam, but that steam is going to cool in the air of the room and condense back into water very quickly.
So I think the real answer to your question is that what you heard is wrong. You can heat steam up to 300 F, but it isn’t going to get that way by itself in a normal house with a normal pot of boiling water.
And let me elaborate a little more on what ChiefScott was saying.
You might have a pipe of really hot water that is under pressure. When water is under pressure, it actually can be hotter than 212 F and still remain as water. This pressurized pipe could contain water that is 300 F. If you cut a hole in the pipe, the pressure would be released and the water would quickly boil. The steam coming out would be the same temp as the water-- 300 F.
So that is an example of a rather unusual senario in which you could have 300 F steam coming off of boiling water.
undead dude, thank you! this is what I was wanting to hear. I couldnt understand how the steam above boiling water could be hotter then the water. Now Im even further convinced (now that someone agrees with me) that what I heard was wrong!
They might be referring to the fact that steam, while no higher in temp than the water, contains much more heat energy. This is due to the fact that the change from water to steam involves adding an amount of energy, called the heat of vaporization, which is released when the steam cools into water on your skin. That’s why steam burns more than water at the same temp.
It is true that steam has substantially more energy at equal termperatures, but it seems to me that the only reason a steam burn might be worse than water burn is due to circumstance. You might be more likely to have a greater amount of steam hit you. If one man dunked his head into 212 F water, and another fellow dunked his head into 212 F steam, I have a feeling that the person who had their head underwater would do much worse. Since water is far more dense, it would have more opportunity to transfer heat. As a matter of fact, while a gram of steam would have more energy than a gram of water at the same temperature, I’m willing to wager that the water would have much more energy per unit volume.
And of course getting burned isn’t really about energy content. It’s about energy transfer. The rate of transfer is dependent on the nature of the materials involved, the nature of the contact between the two materials and the difference in temperature between the two materials. The total thermal energy content is not important.
Yes, I go with this last post of UndeadDude. Steam can be dry or wet with water vapor (droplets suspended in steam and air), both at the same temp. Water has much higher heat conductivity to the skin, whose tissues / nerve endings must be raised in temp to be burned / to sense “ouch”.
Ray
Here’s a scenario where you might have steam at 300 F or higher. Use a pressure cooker. In a pressure cooker, the water has to get hotter that the normal 212 to boil (as was previously alluded to). Steam escaping from this kind of cooker could very well be much higher.
Granted, I don’t know how much hotter, but under enough pressure, 300 sounds reasonable.
Re the pressure cooker: I can’t find my pressure cooker manual right now, but IIRC, at its maximum pressure, 15 lbs, the temp goes up to 240 degrees, which is hot enough to avoid botulism when canning.
Mr. Wizard (on one of the shows that still air occasionally on Nickelodeon) piped steam through a coiled metal tube and heated the coil with a propane torch. Paper held about an inch from the end of the tube in the invisible stream of superheated steam obligingly caught fire.
Well I just can’t pass this one up. Sorry Chief, ex-Navy nuclear engineer turned chemist turned biophysicist here.
First of all, it is entirely possible for steam from boiling water, in an open pot, on your stove, at sea level, on earth to reach temps greater than 212 degrees F. When you heat water to a boil small bubbles start to form on the bottom (or closest to the heat source) of the pot. The bubbles form at nucleation sites usually consisting of imperfections or scratches in the metal (or glass). If the steam forms a bubble, you can rest assured that the pressure inside the bubble (not counting added pressure from the depth of the water, which is negligible) is at 1 atmosphere. Therefore the temp of the steam should be 212 deg F. If, however, you really crank the heat up so that the water is roiling (or, as we say in the biz…bumping) it is more than likely that the steam is superheated. How hot depends on your heat source. So, it is possible (and damn likely too if you cook like me) for steam to be greater than 212. 300? why not?
Be that as it may; that is generally not the reason steam burns are more serious. It’s due to you acting as the heat sink for the latent heat of vaporization which is imparted to you as the steam condenses.
“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
Well, because that would be rather extreme. 
It is true that there really can be a little variation in the temperature, but 300 F would be a little hard to believe. First and foremost, that would require the pot itself, which is constantly being cooled by 212 F water, to be at least 300 F. Second of all, it would require the nucleation to be extremely rare-- you’d need an almost perfect surface.
Between these two factors, I will confidently say that the improbability of this senario is low enough to be neglected in the real world.
And I am confident that this is a misnomer. The idea that steam has much more energy than water at the same temperature assumes an equal mass of steam and water. But the reality is that when steam contacts your skin, the mass that covers a given area is going to be much smaller than the mass of water that would cover that same area. The density difference will be far more important than the difference in thermal energy/mass unit. If need be, I’ll look up the heat of vaporization of water and the density of water and steam at standard pressure. That should settle it.
Now I’m not saying that steam burns aren’t worse. I’m just saying that this isn’t why. Perhaps the typical water burn is like a splash, while the typical steam burn is like a continuous hose spray.
I thought fire was a plasma. Same with lightning.
Fire is not a plasma, but lightning is. Indeed, plasma is quite real. Plasma is any ionized gas, which includes the air that lightning travels in, the gas in neon signs and fluorescent lights, as well as the gases that are so hot that the electrons can’t hold onto the nuclei (like on the Sun or in a nuclear fusion reactor).
I’ll weigh in too. Undead is basically right. The steam cannot be hotter than 212 degree above an open pot. If you place a lid over the pot you will gain a few more degrees, if you use a pressure cooker the steam will get much hotter, as will the water. I don’t have a phase diagram chart, but i imagine that 300 would not be unreasonalble. I can think of no reason that a rolling boil will cause the steam bubbles to reach a higher pressure (ergo temp.) than a simple boil. All that changes is the rate of evaportation. Also, he is correct that the heat of vaporization is small compared to the low density in steam. In short, listen to what UD said.
So what’s fire then? I know this is unrelated to the original topic, but now I’m curious. thx.
Fire is a chemical reaction. It is the rapid combination of various substances (most notably carbon and hydrogen) with oxygen. As oxygen combines with a flammable material, the chemical reaction obviously yields a great deal of heat. The glow of flame is a result of gases combining with oxygen with such a yield of heat that the gas becomes “incandescent”.
Normally, the radiation given off by warm objects in invisible. It is of a lower frequency, generally in the infrared range. When an object gets hotter, the spectrum that it radiates widens into visible light. When this spectrum reaches the point that it produces visible light, the hot object is referred to as being “incandescent”.
So flame appears as a light, for the same reason that a hot poker glows. It is really, really hot.
Re: whether fire is a plasma. These folks say it is: http://www.hmco.com/college/chemistry/resourcesite/digests/chemedl/cednov96/msg00256.htm
I’m not a scientist, so I don’t know the answer, but I’m pretty sure my teachers told me fire was an example of plasma. Has this been a topic of ongoing scientific debate?
(Maybe this should be a separate topic.)