If Oxygen is flammable why dont we blow up while we were using a cigar lighter

[uykusuz]

Oxygen is flammable.But why don't we blow up while we were using a cigar lighter?
I asked this question to my physics teachers..and the told me if the oxygen in air wouldn't be 23 percent we would blow up.This didnt sound true to me.What do you guys think about that?

 

[russ_watters]

Oxygen is not flammable. It is not a fuel, it is an oxidizer. Check a fire triangle.

 

[uykusuz]

sorry i meant cautic..

 

[Necoras]

Oxygen *is* flammable, but it is only one part of the chemical reaction. It requires two other things for a reaction to take place. One is fuel (your lighter fuel or the cigar) the other is ignition energy, (the sparks that fly off of your lighter). Once these three things (O2, lighter fuel, energy) are present in the right mixtures, a chemical reaction occurs and there is flame.

The key variable in your question is the percentage of Oxygen to fuel, and how that affects the amount of energy needed to spark ignition. The higher the percentage of Oxygen in an environment the less energy is needed to start that chemical reaction.

So, if you're in an environment with a very high oxygen content (say, a hyperbaric pressure chamber like those used in some medical treatments) then you require a much smaller amount of energy to start the combustion reaction. You also need less fuel to burn. In a high oxygen environment a small static spark, such as when you touch a doorknob and which would normally do nothing, could set your clothes or hair on fire, or even dust in the air.

You would not spontaneously explode in a high oxygen environment. Also, there wouldn't be a significant difference between the amount of fuel/energy required to start a fire in a 20% vs 25% oxygen environment. Oxygen becomes dangerous when it's very concentrated like in a medical O2 tank.

 

[HallsofIvy]

Oxygen is not flammable.

Oxygen *is* flammable.

That depends upon what you mean by "flammable". It means "will burn" of course, but burning itself is, technically, "oxidation". Normally, we don't think of oxygen as burning.

 

[Necoras]

@HallsofIvy Hrm, I suppose you're right. Technically any oxidizer (including oxygen) is non-flammable. Learned something new today.

 

[mrspeedybob]

Oxygen is not flammable.



That depends upon what you mean by "flammable". It means "will burn" of course, but burning itself is, technically, "oxidation". Normally, we don't think of oxygen as burning.

The only way I can think of to oxidize oxygen would be if you started with a concentration of monatomic oxygen. O combining to form O2 I would think qualifies as oxidation or burning.

 

[S_Happens]

The only way I can think of to oxidize oxygen would be if you started with a concentration of monatomic oxygen. O combining to form O2 I would think qualifies as oxidation or burning.

All oxidation is not burning/fire. Obviously your example shows this, along with other oxidation processes like rusting.

 

[Bill_K]

It's relevant here to mention the fire aboard Apollo 1, in which according to Wikipedia, "... their deaths were attributed to a wide range of lethal hazards in the early Apollo Command Module design and conditions of the test, including a highly pressurized 100% oxygen pre-launch atmosphere."

 

[Femme_physics]

Oxygen *is* flammable, but it is only one part of the chemical reaction. It requires two other things for a reaction to take place. One is fuel (your lighter fuel or the cigar) the other is ignition energy, (the sparks that fly off of your lighter). Once these three things (O2, lighter fuel, energy) are present in the right mixtures, a chemical reaction occurs and there is flame.

The key variable in your question is the percentage of Oxygen to fuel, and how that affects the amount of energy needed to spark ignition. The higher the percentage of Oxygen in an environment the less energy is needed to start that chemical reaction.

So, if you're in an environment with a very high oxygen content (say, a hyperbaric pressure chamber like those used in some medical treatments) then you require a much smaller amount of energy to start the combustion reaction. You also need less fuel to burn. In a high oxygen environment a small static spark, such as when you touch a doorknob and which would normally do nothing, could set your clothes or hair on fire, or even dust in the air.

You would not spontaneously explode in a high oxygen environment. Also, there wouldn't be a significant difference between the amount of fuel/energy required to start a fire in a 20% vs 25% oxygen environment. Oxygen becomes dangerous when it's very concentrated like in a medical O2 tank.

I was just passing through this topic, but very informative...

 

[sophiecentaur]

Saturation divers breathe a mixture of H2 and O2 but there is so much H2 that the mixture is way past the explosive proportion. They DO need to be very careful as they are changing from breathing Air to this mixture, though (no smoking or even the tiniest spark).

 

[cjl]

Saturation divers breathe a mixture of H2 and O2 but there is so much H2 that the mixture is way past the explosive proportion. They DO need to be very careful as they are changing from breathing Air to this mixture, though (no smoking or even the tiniest spark).

Really? I thought they used He and O2. H2 and O2 seems like a very bad combination.

 

[davenn]

Really? I thought they used He and O2. H2 and O2 seems like a very bad combination.

Wiki infers that its a mix of all 3

Extreme depth effectsThe breathing gas mixtures, of oxygen, helium and hydrogen, for extreme depth use are designed to reduce the effects of high pressure on the central nervous system

cheers
Dave

PS I also didnt realize that there was hydrogen in there... my diving mate did hahaha

 

[Drakkith]

It's relevant here to mention the fire aboard Apollo 1, in which according to Wikipedia, "... their deaths were attributed to a wide range of lethal hazards in the early Apollo Command Module design and conditions of the test, including a highly pressurized 100% oxygen pre-launch atmosphere."

Yep. Once there was a spark, the resulting fire had MUCH more oxidizer available than normal. If the oxygen had been near normal levels, it probably would have sparked and smouldered some, not burst into flames like it did.

 

[nucleus]

Compressed oxygen and petroleum products can be a dangerous combination

http://www.hse.gov.uk/pubns/hse8.pdf
http://www.ehow.com/list_7199596_dangers-home-oxygen-use.html

 

[sophiecentaur]

Yep. Once there was a spark, the resulting fire had MUCH more oxidizer available than normal. If the oxygen had been near normal levels, it probably would have sparked and smouldered some, not burst into flames like it did.

Schoolboy test for Oxygen - "Rekindles a glowing splint"

 

[Drakkith]

Schoolboy test for Oxygen - "Rekindles a glowing splint"

Umm, what?

 

[Lsos]

Umm, what?

That's what they taught in school is the test for oxygen: put a glowing hot splint into a gas, and if it rekindles it's oxygen.

I'm not sure of the practical value of this, but it was probably just to illustrate a property of oxygen.

 

[sophiecentaur]

Umm, what?

It was, basically, a response to Post 14.

 

[Drakkith]

It was, basically, a response to Post 14.

Oh. Ok. I didn't really know what you meant and I didn't have time to look up the experiment lol.

 

[davenn]

Oh. Ok. I didn't really know what you meant and I didn't have time to look up the experiment lol.

you missed out on that one in science class ? :( haha awww ;)

D

 

[Drakkith]

you missed out on that one in science class ? :( haha awww ;)

D

Yeah. We didn't really do a lot of experiments in science classes.

 

[rcgldr]

It's relevant here to mention the fire aboard Apollo 1, in which according to Wikipedia, "... their deaths were attributed to a wide range of lethal hazards in the early Apollo Command Module design and conditions of the test, including a highly pressurized 100% oxygen pre-launch atmosphere."

Note it was a combination of pressure and 100% oxygen. In actual space missions, there would be nearly 100% oxygen, but only at 5 psi, and apparently that is reasonably safe. In the Apollo 1 test, they had the oxygen pressurized at atm + 5 psi or about 19.7 psi, which resulted in the fatalities. I assume they were aware of the hazards of 100% oxygen at nearly 20 psi, but I'm not sure why they decided to risk a test operating with such hazards.

 

[sophiecentaur]

If you breathe Oxygen at too high partial pressure, it is toxic. It's highly poisonous to some life forms - anaerobic bacteria, for example - so it must be potentially bad for us. That's a crazy thought. But too much water is also bad for us - drowning etc.
So, as leaks could be a problem in a spacecraft , it seems reasonable to operate at lower pressure but with an atmosphere, rich enough in Oxygen (but similar partial pressure to that on Earth) for the crew to function. It would be no good giving them hypoxia!

 

[Phrak]

Note it was a combination of pressure and 100% oxygen. In actual space missions, there would be nearly 100% oxygen, but only at 5 psi, and apparently that is reasonably safe. In the Apollo 1 test, they had the oxygen pressurized at atm + 5 psi or about 19.7 psi, which resulted in the fatalities.

I assume they were aware of the hazards of 100% oxygen at nearly 20 psi, but I'm not sure why they decided to risk a test operating with such hazards.

They made some quick decisions. They were in a race called the space race for thermonuclear dominance of space. The US won; the Russians lost. It was the cold war--a thermonuclear stand-off on the brink of engagement. There were some war casualties. It must suck to be burnt alive.

According to JFK: "We will go to the moon not because it is easy but because it is hard"--or something like that.

It was pure B*ll-S*it for public dissemination--and it worked marvelously. Invigorated, we bought into the challenge Sputnik represented and tax dollars went to fund this race without opposition. And the Russians were fearful. We landed on the moon, picked up a few rocks and demonstrated beyond doubt that the US could annihilate Moscow and turn her leaders into kings of flies ruling over a thermonuclear wasteland.

 

[nyfith]

oxygen is not flammable, but it can help something burning.

 

[sophiecentaur]

Note it was a combination of pressure and 100% oxygen. In actual space missions, there would be nearly 100% oxygen, but only at 5 psi, and apparently that is reasonably safe. In the Apollo 1 test, they had the oxygen pressurized at atm + 5 psi or about 19.7 psi, which resulted in the fatalities. I assume they were aware of the hazards of 100% oxygen at nearly 20 psi, but I'm not sure why they decided to risk a test operating with such hazards.

I suspect the reason for operating at this high pressure on the ground could have been to equalise the inside and outside pressures. The capsules are as light (hence weak) as possible and could explode or crumple with much pressure difference.

 

[sophiecentaur]

They made quick decisions. They were in a race called the space race. US won. Russians, zero.

And WHO has all the launch vehicles these days? The Russians got up 'there' first. US got to the Moon first - it may well be someone else for the next significant step. There's no point in crowing about a success that was more than 30 years ago. We could discuss the relative merits of spending money on Space or other things.

 

[xxChrisxx]

Yeah. We didn't really do a lot of experiments in science classes.

You mean you didn't do the squeaky pop test either?

 

[alxm]

If you breathe Oxygen at too high partial pressure, it is toxic. It's highly poisonous to some life forms - anaerobic bacteria, for example - so it must be potentially bad for us. That's a crazy thought.

The interesting thing, from my perspective, is why oxygen isn't more reactive. Why don't we all spontaneously burst into flames and burn up? Chemically, that means there must be a high energetic barrier to trigger that reaction. But why? The reaction we learn in school for burning carbon seems simple enough:

C + O₂ --> CO₂

The thing is, that reaction doesn't happen. Not in a single step like that, it's impossible! Because it's not a balanced equation. Chemically balanced, yes, But there's a subtlety here: The angular momentum isn't the same on both sides of the arrow, and angular momentum is conserved!

See, oxygen is a triplet biradical. Biradical meaning it has two unpaired electrons. A triplet means these electrons have the same spin angular momentum (which isn't entirely like angular momentum, but for the sake of this discussion that can be ignored). There are two possible values for it, up or down. And oxygen has two "up" (or "down", doesn't matter) electrons without corresponding electrons with the opposite spin. This is because of the Pauli principle, which says you can't have two electrons with the same spin in the same state. So by having the same spins, the two electrons are more spatially spread-out than they'd have been otherwise, and have lower energy.

But carbon, be it diamond or graphite, has all of its electron spins paired up. So does CO₂ and most molecules, in fact. Which means that oxygen can't do the reaction above, because it means one of the spins has to change orientation, which would violate conservation of angular momentum. The only way it can change the spin orientations is by breaking apart the molecule and forming radicals (which have a single unpaired electron, which is then more or less free to flip its spin).

So basically, you have to do the reaction O₂ --> 2O. You have to break the oxygen-oxygen bond into free oxygen atoms, before the oxygen atoms can then react with carbon. So there's a very high activation energy for that reaction.

On the other hand you have singlet oxygen - which is oxygen where the two electrons are paired. It has higher energy. About 22 kcal/mol higher, which is quite a bit, about as much as a C-C single bond. Due to conservation of angular momentum, it can't immediately lose that energy and become ground-state triplet oxygen. So it's a fairly stable thing, despite having lots of energy and being very reactive. Because unlike ordinary triplet oxygen, it can react directly with ordinary molecules that have all their electrons paired up. It's a dangerous and harmful form of oxygen, and it's sometimes produced in our bodies. In those contexts it (together with superoxo and peroxo oxygen) is called "Reactive Oxygen Species" (ROS). So we've evolved special ROS-scavenging molecules, often with transition-metal atoms (which often have unpaired spins), which go around and find singlet oxygen molecules and flip their spins back so they don't harm us. It's pretty neat.

 

[Phrak]

And WHO has all the launch vehicles these days? The Russians got up 'there' first. US got to the Moon first - it may well be someone else for the next significant step. There's no point in crowing about a success that was more than 30 years ago. We could discuss the relative merits of spending money on Space or other things.

I seem to have made a few additions and clarifications to my post since you read it. Sorry.

As I later implied, it was war, not a foot race.

 

[sophiecentaur]

Fair enough.
I think it's so sad that the poor old Soviets actually felt so totally threatened by the West and spend so much of their meagre GDP on things like space and weapons whilst their population had such poor quality of life. That Stalin has a lot to answer for. Also Churchill and a few others.

 

[Phrak]

I don't know what 'Soviets' are. People are people and leadership are those who almost invariably co-opt a piece of their action, in labor, blood, and whatever it takes to maintain their positions. I know this is far off the topic, but those who also demand you think and feel as they dictate are the most evil and labeled themselves communists. They are not communists, but frauds. By using the label of equality they promote themselves above equality for their own gain. The Russian people themselves have suffered under Czars, communists and now KGB turned mafia for a very, very, very long time. I wish them better.