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Recycled Oxygen Molecules


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#18 Daaisy

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Posted 09 May 2018 - 02:38 AM

Sorry people, am new to this forum thing and hence the posting blunders. But if this logic is true then how do you make sense of what happens when someone smokes. Like for example , lets take a cubicle ( with no air circulation) , and someone smokes in it and exits. He has exhaled CO2 with a strong tobacco smell. So when one enters this closed cubicle after a long time, he can still smell the tobacco- does this mean to say , he s inhaling some of the CO2 of the previous person who was there ??

Edited by Daaisy, 09 May 2018 - 02:39 AM.


#19 pzkpfw

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Posted 09 May 2018 - 03:29 AM

CO2 is one Carbon atom with two Oxygen atoms. You get a lot of those molecules by burning stuff, Carbon in the thing being burned, gets joined with Oxygen from the air (that's simplified).

 

CO2 does not have a tobacco smell. What there is in that room, is the COplus a whole bunch of other molecules (gases, liquid droplets and particles) that came from burning the tobacco.

 

Now someone else who goes into that room, as they breath, they will be taking in some of that CO2 - and other stuff, which is why they smell those smells.

 

(Wikipedia page that includes a list of compounds (e.g. C18H12, C20H12, C2H6N2O, CH2O, ...) that are in tobacco smoke: https://en.wikipedia...i/Tobacco_smoke )

 

 

 

 

If you and someone else are sitting in a room, you are both breathing.

 

You both take in whatever gases are in the air; that will include Nitrogen, Oxygen, CO2, and the stuff that came from the toast you burned.

 

You will both be exhaling CO2 (it's part of how your body works: by reacting Carbon with Oxygen (that's simplified)), and that means some of the CO2 you both breath in later, will have come out of each other.

 

Later, some of that CO2 might be taken in by your house plant, which releases the Oxygen and uses the Carbon to grow (that's simplified).

 

These atoms go around and around, being combined and recombined into different molecules.


Edited by pzkpfw, 09 May 2018 - 03:43 AM.


#20 Daaisy

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Posted 09 May 2018 - 07:54 AM

So u mean to say we r breathing in co2 as well along with oxygen?

#21 exchemist

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Posted 09 May 2018 - 08:09 AM

So u mean to say we r breathing in co2 as well along with oxygen?

Well yes of course. Our atmosphere contains ~400 parts per million (ppm), which is 0.04%, CO2 so we can hardly avoid it. But there is about 21% oxygen, so a lot more of that. Most of the rest is nitrogen (78%), plus some trace gases that make up the remainder, argon being the most important.

 

When we exhale, we exhale a different composition, of course, depleted in oxygen and with more CO2. The composition of exhaled breath is still 78% nitrogen but only 16% oxygen and 4% CO2, plus some water vapour. So in fact there is still a fair amount of oxygen left in exhaled air. 



#22 Daaisy

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Posted 09 May 2018 - 10:03 AM

Wow, this clarifies everything. Thank you so much all. :)

#23 JMJones0424

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Posted 09 May 2018 - 01:55 PM

Sorry people, am new to this forum thing and hence the posting blunders. But if this logic is true then how do you make sense of what happens when someone smokes. Like for example , lets take a cubicle ( with no air circulation) , and someone smokes in it and exits. He has exhaled CO2 with a strong tobacco smell. So when one enters this closed cubicle after a long time, he can still smell the tobacco- does this mean to say , he s inhaling some of the CO2 of the previous person who was there ??

The CO2 isn't what you can smell, as CO2 is odorless.  The partial products of combustion of the cigarette and the combustion of molecules that aren't purely carbon is what produces molecules that we can smell, and like many other molecules that we smell, it is composed of quite complex atomic arrangements.  The act of burning plant materials does not usually result in the ideal combustion process where all products are CO2 and H2O.  The smell you recognize is some of these byproducts of incomplete combustion.

 

So u mean to say we r breathing in co2 as well along with oxygen?

CO2 is a small portion of the air you breathe in, as is oxygen.  The vast majority of the Earth's atmosphere is nitrogen in the form of N2.

https://en.wikipedia...sphere_of_Earth



#24 OceanBreeze

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Posted 10 May 2018 - 02:44 AM

Well yes of course. Our atmosphere contains ~400 parts per million (ppm), which is 0.04%, CO2 so we can hardly avoid it. But there is about 21% oxygen, so a lot more of that. Most of the rest is nitrogen (78%)

 

Yes, and that may cause one to wonder why we have evolved to respirate oxygen instead of the more abundant nitrogen.

I wondered about that myself, at one time. Of course, what I learned is that nitrogen is an inert gas and most (if not all) chemical reactions with nitrogen consume energy. That is, the energy for the reaction is not supplied by the nitrogen but instead is supplied by the other reactant. Basically then, if an organism were to try to respirate nitrogen, the organism would be constantly losing energy instead of gaining any. Hardly a good recipe for survival! Oxygen, on the other hand is high in energy so we benefit from respirating oxygen.

But we do have dissolved nitrogen circulating in our bloodstream; something that I became painfully aware of many years ago when surfacing too quickly from a deep dive. The dissolved nitrogen, upon being depressurized, returns to gas form in the blood which is very painful and can be fatal. That is why deep-sea divers need to surface slowly and undergo depressurization to avoid problems.



#25 exchemist

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Posted 10 May 2018 - 03:57 AM

Yes, and that may cause one to wonder why we have evolved to respirate oxygen instead of the more abundant nitrogen.

I wondered about that myself, at one time. Of course, what I learned is that nitrogen is an inert gas and most (if not all) chemical reactions with nitrogen consume energy. That is, the energy for the reaction is not supplied by the nitrogen but instead is supplied by the other reactant. Basically then, if an organism were to try to respirate nitrogen, the organism would be constantly losing energy instead of gaining any. Hardly a good recipe for survival! Oxygen, on the other hand is high in energy so we benefit from respirating oxygen.

But we do have dissolved nitrogen circulating in our bloodstream; something that I became painfully aware of many years ago when surfacing too quickly from a deep dive. The dissolved nitrogen, upon being depressurized, returns to gas form in the blood which is very painful and can be fatal. That is why deep-sea divers need to surface slowly and undergo depressurization to avoid problems.

Yes, diatomic nitrogen gas is fairly inert due to the very strong N-N triple bond, which requires a lot of energy to break it before the atom is free to react with something else.  But in fact reactions with N2 are quite often exothermic, that is, energy releasing. For instance the formation of ammonia from nitrogen is exothermic. (See Haber Process.) So I'm not sure I entirely buy the idea that a nitrogen-breathing organism would lose energy.

 

What is for sure is that the triple bond presents a huge activation energy barrier to reactions taking place. So I rather think the stability of nitrogen gas is determined as much by kinetics as thermodynamics. 

 

Also I have the idea that oxygen may be relatively reactive because although it has a strong double bond, it has unpaired electrons in the ground state. This enables it to take part in free radical reactions with some ease. So the kinetic barrier to reacting is a lot lower than for nitrogen. 


Edited by exchemist, 10 May 2018 - 03:58 AM.


#26 OceanBreeze

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Posted 10 May 2018 - 04:52 AM

Yes, diatomic nitrogen gas is fairly inert due to the very strong N-N triple bond, which requires a lot of energy to break it before the atom is free to react with something else.  But in fact reactions with N2 are quite often exothermic, that is, energy releasing. For instance the formation of ammonia from nitrogen is exothermic. (See Haber Process.) So I'm not sure I entirely buy the idea that a nitrogen-breathing organism would lose energy.

 

 

I am not 100% sure of that either. There are some denitrifying bacteria that use nitrate in respiration and then release nitrogen gas; the process of denitrification, which I am sure you know about. But nitrate contains more oxygen than nitrogen, so I assume the oxygen is what supplies the energy. As far as I know, nitrogen itself is inert, so I can’t see how energy can be extracted from it, but then again I am not a chemist or a biologist.

I do remember hearing about some organisms that are in symbiotic relationships; with one respirating nitrogen to produce nitrate for another, which in turn respirated the nitrate to provide oxygen for the first, or maybe the reverse, I forget now! These things were deep beneath the sea; that is the only reason why I heard of them.



#27 exchemist

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Posted 10 May 2018 - 11:23 AM

I am not 100% sure of that either. There are some denitrifying bacteria that use nitrate in respiration and then release nitrogen gas; the process of denitrification, which I am sure you know about. But nitrate contains more oxygen than nitrogen, so I assume the oxygen is what supplies the energy. As far as I know, nitrogen itself is inert, so I can’t see how energy can be extracted from it, but then again I am not a chemist or a biologist.

I do remember hearing about some organisms that are in symbiotic relationships; with one respirating nitrogen to produce nitrate for another, which in turn respirated the nitrate to provide oxygen for the first, or maybe the reverse, I forget now! These things were deep beneath the sea; that is the only reason why I heard of them.

This about nitrogen fixation is interesting but tantalising.:https://en.wikipedia...trogen_fixation

 

It says metallo-enzymes are involved in the symbiotic bacteria that fix nitrogen for use by leguminous plants, but gives no details. I imagine N2 can bind to transition metals rather as oxygen does in haemoglobin, but I have not idea of what exactly happens. But it will be a catalytic process, by which the activation energy for reaction is somehow lowered. 



#28 JMJones0424

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Posted 11 May 2018 - 08:34 PM

I am digging back more decades than I care to admit, so take everything that follows with a grain of salt.

 

The energy contained in a molecular bond is not "released" when it is broken, instead, it requires energy to break it.  However, in some cases, the energy required to break the bond is less than the energy required to make a new bond, and in cases like this, the reaction is exothermic.  N2 is relatively stable, and is a poor candidate for an oxidizer because it requires a comparatively tremendous amount of energy to break the chemical bond.  Oxygen, on the other hand, will readily combine with nearly anything while the oxygen to oxygen bond is weak.

 

It is true that some microorganisms consume N2 to produce NH3, but as far as I know, this process doesn't result in energy useful to the organism.  ***There's a good chance that this is wrong, I don't know***  Other than cyanobacteria, it must be in a symbiotic relationship with an acceptable host and is a consumer of sugars from the host and produces bio-available nitrogen in return.  How this evolved is beyond me.  Lightning can also produce ammonia, and diesel engines especially produce NOx gasses from N2 and O2 in a high temperature and high pressure environment.

 

Other very good oxidizers include ozone, hydrogen peroxide, flourine and other halogens, nitrates, sulfates...  N2 is not a good oxidizer because it is a very hard bond to break.

 

Another way to look at it is that N2 is the low end of the potential energy spectrum, in order to break the bond, you generally have to expend more energy than you gain by combining the nitrogen atoms with other atoms.  However, O2 is way up near the top, as the energy required to break the bond is very low compared to the energy released when new bonds are formed with other elements.  The only reason we even have a measurable amount of O2 in our atmosphere is because living organisms store solar (or chemical?) energy by making chemical bonds that release O2 and then later bring that oxygen back to release energy.  I think that the prevalence of O2 is a positive sign of life, and would otherwise not naturally occur in measurable levels.


Edited by JMJones0424, 11 May 2018 - 08:46 PM.


#29 exchemist

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Posted 12 May 2018 - 06:06 AM

I am digging back more decades than I care to admit, so take everything that follows with a grain of salt.

 

The energy contained in a molecular bond is not "released" when it is broken, instead, it requires energy to break it.  However, in some cases, the energy required to break the bond is less than the energy required to make a new bond, and in cases like this, the reaction is exothermic.  N2 is relatively stable, and is a poor candidate for an oxidizer because it requires a comparatively tremendous amount of energy to break the chemical bond.  Oxygen, on the other hand, will readily combine with nearly anything while the oxygen to oxygen bond is weak.

 

It is true that some microorganisms consume N2 to produce NH3, but as far as I know, this process doesn't result in energy useful to the organism.  ***There's a good chance that this is wrong, I don't know***  Other than cyanobacteria, it must be in a symbiotic relationship with an acceptable host and is a consumer of sugars from the host and produces bio-available nitrogen in return.  How this evolved is beyond me.  Lightning can also produce ammonia, and diesel engines especially produce NOx gasses from N2 and O2 in a high temperature and high pressure environment.

 

Other very good oxidizers include ozone, hydrogen peroxide, flourine and other halogens, nitrates, sulfates...  N2 is not a good oxidizer because it is a very hard bond to break.

 

Another way to look at it is that N2 is the low end of the potential energy spectrum, in order to break the bond, you generally have to expend more energy than you gain by combining the nitrogen atoms with other atoms.  However, O2 is way up near the top, as the energy required to break the bond is very low compared to the energy released when new bonds are formed with other elements.  The only reason we even have a measurable amount of O2 in our atmosphere is because living organisms store solar (or chemical?) energy by making chemical bonds that release O2 and then later bring that oxygen back to release energy.  I think that the prevalence of O2 is a positive sign of life, and would otherwise not naturally occur in measurable levels.

Yes it is interesting. I've now looked up some more numbers. The formation of ammonia gas from hydrogen and nitrogen is exothermic at ambient temperatures by 46kJ/mol, so the reaction could provide some energy to the organism. At any rate it does not consume energy. However, by comparison, the formation of water (vapour, to keep it like for like) is much more strongly exothermic, releasing 242kJ/mol. So this provides some support for the idea that oxygen is intrinsically more likely to take part in energy-releasing reactions. But in both cases, the reaction of the element with hydrogen does release energy. 

 

So the main hurdle to overcome is the kinetic barrier (breaking the N-N bond), not the thermodynamics. A catalyst is therefore required. I looked up how the enzyme works in the bacteria associated with legumes and it seems to be a really complicated system, involving both iron and molybdenum(!) atoms: https://en.wikipedia...iki/Nitrogenase

 

There are apparently also other enzymes using vanadium, and some using iron alone. But this is clearly one of those cases in which life has had to call on the transition metals to form metal-N2 complexes, just as life calls on iron to form a Fe-O2 complex in haemoglobin. 



#30 DaveC426913

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Posted 02 June 2018 - 06:40 PM

Just to confound things further, oxygen atoms exchange their electrons as they undergo various chemical processes. (eg. in high atmo, )2is broken down into monatomic oxygen. They will lose some electrons)

 

Since an atom is a composition of its protons AND electrons (otherwise it's just a nucleus), technically even oxygen atoms are changing all the time.


Edited by DaveC426913, 02 June 2018 - 06:41 PM.


#31 exchemist

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Posted 03 June 2018 - 02:55 PM

Just to confound things further, oxygen atoms exchange their electrons as they undergo various chemical processes. (eg. in high atmo, )2is broken down into monatomic oxygen. They will lose some electrons)

 

Since an atom is a composition of its protons AND electrons (otherwise it's just a nucleus), technically even oxygen atoms are changing all the time.

Hmm, I"m not sure you can say that. Electrons are indistinguishable and cannot be tracked, due to the uncertainty in QM. You can sort of track nuclei, if you have different isotopes, and thereby show that atoms migrate in a certain manner as a result of the reactions they undergo. But not with electrons.