238
votes
Accepted
Why doesn't water burn?
You can think of water as the ash from burning hydrogen: it's already given off as much energy as possible from reacting hydrogen with oxygen.
You can, however, still burn it. You just need an even ...
- 2,187
114
votes
Why doesn't water burn?
This is the reaction that occurs when hydrogen combusts:
$$
\ce{2H2 + O2 -> 2H2O}
$$
Similarly, this is the combustion reaction for methane, a representative fuel:
$$
\ce{CH4 + 2O2 -> CO2 + ...
- 17.4k
54
votes
Why does wood burn but not sugar?
Combustion is a gas phase reaction. The heat of the flame vapourises the substrate and it's the vapour that reacts with the air. That's why heat is needed to get combustion started.
Anyhow, wood ...
- 1,993
47
votes
Why doesn't water burn?
$\ce{H2O2}$ exists, and could be what you expect by burning water (since burning is really oxidizing, or adding oxygen.)
However, in stoichiometric proportions, here is what would happen:
Either ...
- 579
43
votes
Accepted
Why doesn't NASA or SpaceX use ozone as an oxidizer for rocket fuels?
As is usual with rocket fuels, the problems of ozone are practicality not performance
Almost every answer for why a specific rocket fuel component is used or not will end up referring to John D Clarke'...
- 37.1k
38
votes
Accepted
Does any known substance ignite on cooling?
Actually... yes! Iron(II) oxide is thermodynamically unstable below $848~\mathrm K$. As it cools down to room temperature (it has to do it slowly) it disproportionates to iron(II,III) oxide and iron:
...
- 2,098
33
votes
Accepted
When a candle burns, why does the top of wick glow if bottom of flame is hottest?
The wick temperature does not have to be the same as the flame temperature.The flame is hottest at the bottom, but the wick is hottest at the top.
For a candle, the wick burning isn't the intended ...
- 12.7k
32
votes
Would the concentration of oxygen around fire increase as we get close to the fire (from the outside)
A fire has no way to directly "draw in" oxygen for it to burn. It consumes what oxygen is in the immediate vicinity of the flame, depleting the air in oxygen compared to the concentration of oxygen in ...
- 17.6k
29
votes
When a candle burns, why does the top of wick glow if bottom of flame is hottest?
Because fire is not the same thing as light.
Michael Faraday did a wonderful job of explaining how the candle works, and I direct you to look at it (there are also Youtube videos giving a modern take ...
- 17.5k
27
votes
Can flames be colored black?
This video shows how a black flame is achieved. If you illuminate the fire with a monochromatic light source (sodium vapor lamp) and introduce a species in the fire that absorbs that wavelength (...
- 321
25
votes
Accepted
How do self-relighting (trick) birthday candles work?
In normal candles, as you blow them out, you will see burning embers in the candles, which vaporises the wax and thus causes a ribbon of paraffin wax to rise up (this looks like a wisp of smoke). ...
- 652
23
votes
Accepted
On heating in the Earth's atmosphere, can magnesium react with nitrogen to form magnesium nitride?
A large pile of grey magnesium powder, when lit in air, produces a smouldering pile which cools down to reveal a crusty white solid of magnesium oxide. However, if you break apart the mound, you can ...
- 29.1k
23
votes
Where does the energy from combustion come from?
Better is to say "Energy released by forming bonds of combustion products is bigger than the energy needed to break bonds of combustion reactants.".
Particularly breaking $\ce{C-C}$, $\ce{C-...
- 43.3k
21
votes
When I burn isopropyl alcohol (IPA), it burns orange. But when I burn ethyl alcohol, it burns totally blue. Why is this?
IPA has a different carbon:hydrogen ratio than ethanol. There is more incomplete combustion occurring with IPA, hence the smoky orange flame and smell of soot. Ethanol combusts more completely, ...
- 477
20
votes
What is going on in and below a yellow or blue gas flame?
The yellow emission has a continuous spectrum. So it is not due to an atom or of a molecule. It is due to a solid black body, hot enough to emit light (about $1000$°C). The solid stuff is solid carbon ...
- 29.5k
19
votes
Can diamond undergo a self sustaining combustion reaction all the way to carbon dioxide?
Yes, diamond will combust in air. Regardless of the ambient air temperature, e.g. your example of $21\ \mathrm{^\circ C}$, you of course have to heat it to it's ignition temperature somehow, whether ...
- 17.6k
19
votes
Are all volatile liquids combustible?
Many volatile liquids are not combustible
Dichloromethane (DCM) is a widely used solvent by chemists. It boils at around 40°C (the same as diethyl ether) but is not remotely combustible or flammable. ...
- 37.1k
19
votes
Accepted
Does all fire only emit light on its outermost shell?
The answer is NO.
The article you quote makes a completely unwarranted generalisation that "all flames are hollow". This is true of some flames but only because the fuel that is burning is ...
- 37.1k
18
votes
What single, pure compound would best replace petrol?
Higher $\mathrm{RON}$ seems possible. Yet the boiling point rises accordingly while heat of combustion remains roughly the same. Here are two compounds that fit all posed criteria.
\begin{array}{|c|c|...
- 7,169
18
votes
Accepted
When I burn isopropyl alcohol (IPA), it burns orange. But when I burn ethyl alcohol, it burns totally blue. Why is this?
Interesting observation. The blue flame color of all hydrocarbon fuels is due to the emission small diatomic carbon species such $C_2$ or CH. There is nothing magical about IPA having a yellow flame. ...
- 42.2k
17
votes
How can solids undergo combustion if it only occurs in the gas phase?
Combustion is a gaseous phase phenomenon. Oil and gasoline have a high enough vapor pressure at ambient temperatures to produce a gaseous phase of fuel above the liquid. In contrast, hold a lighter up ...
- 24.1k
17
votes
Why doesn't water burn?
This becomes intuitive once you accept that any chemical compound will 'want' to be in the state with the lowest energy, the ground state for a given temperature and pressure. For example, if you plot ...
- 456
17
votes
Accepted
Carbon tetraradical
In its ground state, naked carbon is triplet $^3P$, with two metastable singlet states $^1D$ and $^1S$ ($^1D$ being the one that participates in most reactions) while the tetraradical is the least ...
- 14.4k
16
votes
Accepted
What is the mechanism of alkane combustion?
The following, very general radical reactions apply to any common combustion reaction of organic material. Details vary largely.
Step 1
An energy spark of whatever kind turns triplet oxygen into its ...
- 12.2k
15
votes
Why doesn't the carbon dioxide produced by a fire put out said fire?
The fuel for the chemical reaction is the CH4 (in this case) and the oxygen. Assuming the CH4 isn't going to run out any time soon, the chemical reaction will continue as long as there is enough ...
- 301
15
votes
Why doesn't NASA or SpaceX use ozone as an oxidizer for rocket fuels?
Liquid ozone is rather stable (as in "can be stored") as an up to 70% solution in LOx, if you add some stabilisers. That would give quite a bit of additional boost in a rocket, but it's ...
- 12.2k
14
votes
Accepted
Is oxygen necessary for burning?
Yes, absolutely. Burning refers to oxidation accompanied by a flame and there are numerous reactions in which oxygen takes no part. Most of these are either with elementary halogens, or compounds ...
- 7,169
13
votes
Why is oxygen so special?
Dioxygen, $\ce{O2}$ is a very special molecule. A good majority of organisms on earth use dioxygen to breathe and survive. Oxygen is also the second most abundant element in the sky, as well as the ...
13
votes
Accepted
What is behind of the attraction between a burned matchstick with a magnet?
Some matchstick heads contain iron(III) oxide as a colorant.
The yellowish color of the burning match indicates that it has low oxygen, i.e. a reducing flame. It reduces the iron oxide to iron which ...
- 7,260
12
votes
Accepted
How does heptafluoropropane suppress fire?
Curt F. is probably correct in his estimate that heptafluoropropane extinguishes fire primarily by physical means. According to an overview by Choy and Fong, 'An Introduction to Clean Agents: ...
- 7,169
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