# Chemical reasons in vacuum **URL:** \ **Category:** Factual Questions\ **Created:** [July 14, 2011, 1:25pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007 "2011-07-14T13:25:40Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Seraphist](https://avatars.discourse-cdn.com/v4/letter/s/5f9b8f/32.png) [@Seraphist](https://boards.straightdope.com/u/Seraphist)\ **Post date:** [July 14, 2011, 1:25pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/1 "2011-07-14T13:25:40Z")
I know there’s already been conversations here about burning stuff in a vacuum. However I couldn’t find this part of the conversation that I thought would’ve popped up. If something is burning in a vacuum, say thermite or another self supplying chemical reaction. What happens to all the energy to be released as heat? Radiation is obvious but where does the energy that would transfer via convection or Conduction supposed to go? Would all thermal energy be released via radiation? Is that even possible? Is there some fundamental of chemistry/physics i’m missing out on? ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [July 14, 2011, 1:32pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/2 "2011-07-14T13:32:07Z")
Well, I think most of the energy, even when there isn’t a vacuum, goes to heating (i.e. speeding up) the reacting molecules. Now in an atmosphere, that heat is going to be gradually transferred to the air by contact, and carried away by conduction/convection in the air, but every fire I’ve seen, the reacting stuff gets pretty hot and stays hotter than the atmosphere for a while. So I think the absence of air (assuming oxidizer is present) isn’t going to make a huge difference – the coals will get a little hotter, and stay hotter a little longer, but overall not a major change. ---
**Author:** ![BowlOfDucks](https://avatars.discourse-cdn.com/v4/letter/b/2bfe46/32.png) [@BowlOfDucks](https://boards.straightdope.com/u/BowlOfDucks)\ **Post date:** [July 14, 2011, 1:32pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/3 "2011-07-14T13:32:50Z")
Conduction and convection is when rapidly vibrating atoms hit less rapidly vibrating atoms, speeding them up. No atoms in a vacuum, so no conduction and convection. Radiation would still work. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [July 14, 2011, 1:57pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/4 "2011-07-14T13:57:54Z")
> [@Quercus](#): > > the coals will get a little hotter, and stay hotter a little longer, but overall not a major change. \*Much \*longer, I would say. The experiment is taking place in a vacuum-insulated environment. The thermite reacts, creating a blob of molten iron and hot alumina cinders that will stay hot for a lot longer than it would in atmosphere. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [July 14, 2011, 2:17pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/5 "2011-07-14T14:17:41Z")
same amount of energy produced with fewer ways of dispersing it, so it will take longer to disperse. in a vacuum chamber with gravity the particles would hit the container walls and loose energy through conduction. ---
**Author:** ![Seraphist](https://avatars.discourse-cdn.com/v4/letter/s/5f9b8f/32.png) [@Seraphist](https://boards.straightdope.com/u/Seraphist)\ **Post date:** [July 14, 2011, 2:33pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/6 "2011-07-14T14:33:35Z")
So there would just be a pile of hot leftovers with no means of cooling short of slowly radiating heat? ---
**Author:** ![Seraphist](https://avatars.discourse-cdn.com/v4/letter/s/5f9b8f/32.png) [@Seraphist](https://boards.straightdope.com/u/Seraphist)\ **Post date:** [July 14, 2011, 2:56pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/7 "2011-07-14T14:56:20Z")
So there would just be a pile of hot leftovers with no means of cooling short of slowly radiating heat? ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [July 14, 2011, 3:03pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/8 "2011-07-14T15:03:20Z")
Don’t quote me on this, but I suspect there would just be a pile of hot leftovers with no means of cooling short of slowly radiating heat. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [July 14, 2011, 3:59pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/9 "2011-07-14T15:59:25Z")
> [@Seraphist](#): > > So there would just be a pile of hot leftovers with no means of cooling short of slowly radiating heat? Yes, that is correct. This is actually a large problem with spacecraft; you have to radiate away both the heat from incident sunlight and from internal power generation and operating processes, but you have only the limited surface area on the craft where you can place outward-facing radiators. This is why the STS Space Shuttle has the cargo bay doors open as soon as it is on orbit; radiators are mounted on the inside of the doors and are needed to keep the cabin habitable by radiating heat away from the fuel cells. The original design for the model of _Discovery_ in _2001: A Space Odyssey_ actually had massive cooling fins on the rear reactor/propulsion module, but Kubrick had them removed because he feared the audience would believe them to be aerodynamic wings, which would make no sense on an interplanetary spacecraft. Stranger ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [July 14, 2011, 4:08pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/10 "2011-07-14T16:08:57Z")
Of course, an object burning in a vacuum would send off a lot of its heat with by-products of the reaction itself, like smoke. These gases and particulates could only lose their own heat by radiation, but you won’t have all the thermal energy staying with the remaining cinders. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 14, 2011, 5:33pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/11 "2011-07-14T17:33:55Z")
> [@Seraphist](#): > > So there would just be a pile of hot leftovers with no means of cooling short of slowly radiating heat? Evaporation too, if the “pile of leftovers” is hot enough (or contains volatile materials). ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [July 14, 2011, 6:08pm UTC](https://boards.straightdope.com/t/chemical-reasons-in-vacuum/589007/12 "2011-07-14T18:08:56Z")
Of course, if the burning takes place on the moon instead of in orbit, the reaction products are going to be sitting on the reaction vessel instead of floating, and so they’ll transfer heat via conduction to the reaction vessel, which transfers heat via condution to the lunar regolith.