# Endothermic Fire **URL:** \ **Category:** Factual Questions\ **Created:** [April 29, 2009, 9:56pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779 "2009-04-29T21:56:31Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [April 29, 2009, 9:56pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/1 "2009-04-29T21:56:31Z")
Ok, is there such a thing? Back in my school chemistry days, someone claimed that he had seen a video of someone burning a flammable liquid in their hand, and being unhurt since it was an endothermic reaction. Juvenile legend, or fact? ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [April 29, 2009, 11:14pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/2 "2009-04-29T23:14:44Z")
Were there flames (and if not, in what sense was it “burning”)? I don’t think an endothermic reaction could produce flames. Of course, fire eaters and the like do all sorts of tricks where it looks as though they ought to be burning themselves but they do not, but it is regular exothermic fire they are working with. ---
**Author:** ![Silophant](https://avatars.discourse-cdn.com/v4/letter/s/a698b9/32.png) [@Silophant](https://boards.straightdope.com/u/Silophant)\ **Post date:** [April 29, 2009, 11:34pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/3 "2009-04-29T23:34:41Z")
Correct me if I’m wrong, but I think visible flames are just particles of dust and other products of combustion, heated to the point where they glow. So if it was an endothermic reaction, there wouldn’t be visible flames. ---
**Author:** ![acetylene](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@acetylene](https://boards.straightdope.com/u/acetylene)\ **Post date:** [April 29, 2009, 11:49pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/4 "2009-04-29T23:49:07Z")
Chemistry teacher here. This is one of my favorite demonstrations. it’s called the methane mamba. Run a tube connected to a source of natural gas (methane) into a container with soapy water. Bubbles will form. The bubbles are filled with methane instead of air, so they will rise. but they stick together so you get a rising column of very flammable, and very stinky, bubbles. WET YOUR HAND! Then break off the column at the bottom so it sticks to your hand, going upwards. Light it and listen to the oohs and aaahs. It doesn’t burn your hand because a) the heat rises and your hand is underneath it, and b) your hand is wet The combustion of methane is definitely exothermic, though, as anyone standing near it can tell you. [Here is a video.](http://www.youtube.com/watch?v=AopbZW_w_q8&feature=related) There are lots of them on youtube. ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [April 30, 2009, 12:04am UTC](https://boards.straightdope.com/t/endothermic-fire/494779/5 "2009-04-30T00:04:19Z")
> [@acetylene](#): > > Chemistry teacher here. This is one of my favorite demonstrations. it’s called the methane mamba. > > Run a tube connected to a source of natural gas (methane) into a container with soapy water. Bubbles will form. The bubbles are filled with methane instead of air, so they will rise. but they stick together so you get a rising column of very flammable, and very stinky, bubbles. WET YOUR HAND! Then break off the column at the bottom so it sticks to your hand, going upwards. Light it and listen to the oohs and aaahs. It doesn’t burn your hand because a) the heat rises and your hand is underneath it, and b) your hand is wet > > The combustion of methane is definitely exothermic, though, as anyone standing near it can tell you. > > [Here is a video.](http://www.youtube.com/watch?v=AopbZW_w_q8&feature=related) There are lots of them on youtube. Pfah ! That’s a pussy trick. Try [dipping your hand in molten lead](http://www.wiley.com/college/phy/halliday320005/pdf/leidenfrost_essay.pdf) to demonstrate the Leidenfrost effect (PDF link) 😃 ---
**Author:** ![IAmNotSpartacus](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@IAmNotSpartacus](https://boards.straightdope.com/u/IAmNotSpartacus)\ **Post date:** [April 30, 2009, 12:45am UTC](https://boards.straightdope.com/t/endothermic-fire/494779/6 "2009-04-30T00:45:31Z")
Well, I’ve burned alcohol in my hand before, it didn’t hurt, but I don’t think it was endothermic either. ---
**Author:** ![acetylene](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@acetylene](https://boards.straightdope.com/u/acetylene)\ **Post date:** [April 30, 2009, 1:41am UTC](https://boards.straightdope.com/t/endothermic-fire/494779/7 "2009-04-30T01:41:33Z")
> [@Kobal2](#): > > Pfah ! That’s a pussy trick. Try [dipping your hand in molten lead](http://www.wiley.com/college/phy/halliday320005/pdf/leidenfrost_essay.pdf) to demonstrate the Leidenfrost effect (PDF link) 😃 I wish I could do that. I’ve seen it before. For better or for worse, lead, along with mercury and a lot of other substances, are a big no-no in HS chem labs nowadays. BTW, I’ve had flaming alcohol on my hands before too, but I doubt that’s what the OP’s friend was referring to because alcohol doesn’t burn very brightly. And yes, the combustion of any alcohol is also exothermic, not endothermic. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [April 30, 2009, 3:47am UTC](https://boards.straightdope.com/t/endothermic-fire/494779/8 "2009-04-30T03:47:32Z")
> [@acetylene](#): > > Chemistry teacher here… Hey, welcome to the SDMB! (Though I see that you’ve been here for a couple of months.) Nice to see another chemistry teacher here. I taught chemistry several years ago back when I was in the Navy. > [@acetylene](#): > > I wish I could do that. I’ve seen it before. For better or for worse, lead, along with mercury and a lot of other substances, are a big no-no in HS chem labs nowadays. I used to pass around lead in class (in a ziplock bag) just so students could appreciate how malleable it is. I also used to pass around a good-sized container of mercury (~500 mL), before I decided that it was only a matter of time before somebody dropped it–so I stopped doing that. ---
**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\ **Post date:** [April 30, 2009, 4:01am UTC](https://boards.straightdope.com/t/endothermic-fire/494779/9 "2009-04-30T04:01:50Z")
Most likely your friend was describing a regular exothermic flame but one which was burning at a relatively low temperature. IIRC, acetone will burn at a temperature which would not be harmful if it were in your hand at the time. ---
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [April 30, 2009, 10:11am UTC](https://boards.straightdope.com/t/endothermic-fire/494779/10 "2009-04-30T10:11:09Z")
Ok follow up question, is there such a thing as an endothermic fire? ---
**Author:** ![acetylene](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@acetylene](https://boards.straightdope.com/u/acetylene)\ **Post date:** [April 30, 2009, 2:24pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/11 "2009-04-30T14:24:08Z")
I would have to say no. Fire is the combustion of a fuel (Hydrogen or some carbon compound) with oxygen. Hydrogen and oxygen gases combine to make **water** (and heat). Think Hindenburg. A carbon compound (anything from methane to propane to wood, which contains cellulose) will combine with oxygen to form **carbon dioxide** and **water.** These reactions always release heat. See this page. Looking at the delta H column, notice how almost all of them have negative values. That means they form exothermically. This is true of both **carbon dioxide** and **water**. There certainly are endothermic reactions, but none that could be considered fire. I would love to know of any exceptions to this. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [April 30, 2009, 3:36pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/12 "2009-04-30T15:36:41Z")
> [@acetylene](#): > > …Fire is the combustion of a fuel (Hydrogen or some carbon compound) with oxygen… More generally, fire is the rapid oxidation of combustible material that releases energy. The oxidizing agent may indeed be oxygen, but does not have to be. Other oxidizing agents that can produce fire include chlorine and fluorine. I agree that an endothermic fire would not be possible. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [April 30, 2009, 5:51pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/13 "2009-04-30T17:51:41Z")
> [@robby](#): > > I agree that an endothermic fire would not be possible. But it would make an _awesome_ band name. 🙂 ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [April 30, 2009, 6:35pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/14 "2009-04-30T18:35:59Z")
> [@acetylene](#): > > I wish I could do that. I’ve seen it before. For better or for worse, lead, along with mercury and a lot of other substances, are a big no-no in HS chem labs nowadays. How about liquid nitrogen in your mouth or a bed of hot coals under your feet ? That works too 😉 But it even those are barred, never fear : there’s always Jearl’s “bed of nails” demonstration, in which he lets himself be sandwiched between two flat boards with lots of nails in ‘em, then asks a student to wield the heavy mallet that’ll smash the cinderblock propped on top of the nail sandwich. The point is that it can’t hurt the sandwichee for real, because the point-to-point force of the mallet hitting the cinderblock spreads over the whole surface of the cinderblock, then again across the entire surface of the upper bed o’ nails, so the nails never ever penetrate the skin. But as he says, “any experiment during which the teacher looks like he may die or be injured for life is a good one”. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [April 30, 2009, 7:01pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/15 "2009-04-30T19:01:46Z")
On the other hand, we do have a Dutch former SDMB moderator who might qualify! 😃 ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [April 30, 2009, 7:04pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/16 "2009-04-30T19:04:46Z")
> [@AK84](#): > > Ok follow up question, is there such a thing as an endothermic fire? A self sustaining endothermic reaction requires that the term T(delta)S is greater than the enthalpy (delta H) of the reaction. You can do this by raising the temperature of a reaction where the entropy is positive, but since the reaction is endothermic, the temperature will not sustain itself. If the deltaS of the reaction is high enough, then the temperature can be lower. Even so, the TdeltaS term will eventually be equal to the enthalpy term as heat is taken from the system. So no endothermic reaction can be self sustaining. I would say that this rules out any endothermic fire even if you don’t limit yourself to hydrocarbon combustion. ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [April 30, 2009, 8:26pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/17 "2009-04-30T20:26:59Z")
> [@Kobal2](#): > > But it even those are barred, never fear : there’s always Jearl’s “bed of nails” demonstration, in which he lets himself be sandwiched between two flat boards with lots of nails in ‘em, then asks a student to wield the heavy mallet that’ll smash the cinderblock propped on top of the nail sandwich. The point is that it can’t hurt the sandwichee for real, because the point-to-point force of the mallet hitting the cinderblock spreads over the whole surface of the cinderblock, then again across the entire surface of the upper bed o’ nails, so the nails never ever penetrate the skin. But as he says, “any experiment during which the teacher looks like he may die or be injured for life is a good one”. Any experiment of that sort is also the sort of thing where eventually something is going to go horribly wrong for at least one practitioner. ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [April 30, 2009, 10:16pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/18 "2009-04-30T22:16:50Z")
> [@WarmNPrickly](#): > > So no endothermic reaction can be self sustaining. Evaporation is endothermic, but the entropy created makes the overall reaction self sustaining. ---
**Author:** ![Public\_Animal\_No.9](https://avatars.discourse-cdn.com/v4/letter/p/b9e5f3/32.png) [@Public\_Animal\_No.9](https://boards.straightdope.com/u/Public_Animal_No.9)\ **Post date:** [April 30, 2009, 10:29pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/19 "2009-04-30T22:29:33Z")
I think the basic definition of combustion includes heat release, so by definition, fire is exothermic. I can’t recall any classroom discussion of the combustion process - including several graduate courses (one of them exceedingly tedious!) on the topic - that did not begin with the premise that heat was released. ---
**Author:** ![Khadaji](https://avatars.discourse-cdn.com/v4/letter/k/9e8a1a/32.png) [@Khadaji](https://boards.straightdope.com/u/Khadaji)\ **Post date:** [April 30, 2009, 10:40pm UTC](https://boards.straightdope.com/t/endothermic-fire/494779/20 "2009-04-30T22:40:01Z")
My chemistry teacher told us about a type of paraffin that burned at a very low heat, such that you could coat your hand with it and light it. But he didn’t know how to make it and we never heard more than that tale. I suspect he was either mistaken or having us on. [Next page](https://boards.straightdope.com/t/endothermic-fire/494779.md?page=2)