I'm learning on my own with Chemistry The Central Science, 13th ed. book. So far it's going well.

I've come across something I don't think I understand. I've googled and "stackechanged" with no avail.

How come a combustion generates no gas products? And in what circumstances? This is the bit of the book that left me wondering:

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For a noob like me, it's counterintuitive that something "burns brilliantly in air" and only generate solid products.

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    $\begingroup$ Well, the answer is: just like that. You ignite magnesium, it burns with a flash that leaves you blind for a minute or so, and produces nothing but $\ce{MgO}$ which has pretty high melting point (and even higher boiling point, of course). Who said a combustion must always generate gas products? $\endgroup$ – Ivan Neretin Mar 21 '16 at 13:45
  • $\begingroup$ If $\ce{CO2}$ and $\ce{CO}$ weren't gaseous, then hydrocarbons would burn to form essentially all solid products, too. $\endgroup$ – hBy2Py Mar 21 '16 at 14:22
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    $\begingroup$ I guess the exact definition of combustion collides a little bit with my natural experience. I'll work on that. $\endgroup$ – Carles Alcolea Mar 21 '16 at 15:02
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    $\begingroup$ It should be noted that to the eye, there will be a lot of off gassing if you actually try this, but that is largely due to the extremely high temperature of magnesium burning igniting impurities present in the magnesium ribbon. This is one case where the chemical prediction will differ from the pragmatic observation. If you burned pure magnesium there would be no off-gassing. $\endgroup$ – Lighthart Mar 21 '16 at 15:06
  • $\begingroup$ I think the issue is that a kind of burning like this one could generate a smoke of solid particles. I guess that would fit with the "natural experience"; would it fit with the chemical issue at hand? $\endgroup$ – Carles Alcolea Mar 24 '16 at 0:59

There are many reactions that do this. The simplest way is to substitute any other reactive metal for magnesium: aluminium, lithium, sodium, etc. All will burn in oxygen to give solid products / oxides.

This can be extended by using any of these metals and other reactive non metals, such as fluorine, chlorine, etc. in Group VII or sulphur, etc. in Group VI. Do not try it with $\ce{Se}$ or $\ce{Te}$ in combination with aluminium, however, as it is near-explosive and forms toxic gas on hydrolysis.

A simple experiment that does this is the reaction of sulphur with iron filings.

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    $\begingroup$ Welcome to Chem.SE! Thanks for posting your answer here. I've reformatted your post to make it more readable, and made some edits (removed element name capitalization, etc.) to bring it in conformity to site standards. $\endgroup$ – hBy2Py Mar 21 '16 at 14:27

In our rocket club we used 1:1 mol/mol mix of zinc dust and flowers of sulphur as our basic rocket fuel. The product is ZnS - no gas. It burned with a bright green flame and produced a beautiful dense cloud & trail of white ZnS smoke. The expansion was due simply to the extreme heating of the air in between the fuel/oxidizer particles.


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