pop's opinion: CARBON DIOXIDE a story - Page 2 - Tropical Fish Keeping - Aquarium fish care and resources
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post #11 of 13 Old 06-18-2013, 07:41 AM Thread Starter
Hello Mikaila31,

You have out done yourself with this post and I really like this particular notion of ‘as things are always pushed towards equilibrium.’ I also wanted to thank you for the definitive definition of osmosis.

You took me back a little with the density argument until I started to understand your notion. As pointed out temperature effects the ability of water molecules to accept CO2 assimilation while at the same time alters the density of the water molecule. These might be two separate and independent processes that occur at the same time. One would think that as water molecule cools it becomes more dense there fore reducing the surface area of the molecule and should restrict the diffusion of CO2; of course when considering pressure it would require greater pressure to move CO2 into this dense molecule.

As I understand the solubility of carbon dioxide and its affinity for water is reduced as the water column temperature increases. Another way to conceive this process in cooler waters molecules move slower giving each water molecule increased time to absorb the dissolved carbon dioxide molecule.

I very much agree with this “However usually one compound, CO2, in this case does not become stratified without the same happening to other compounds and parameters like O2 and temperature.” This perfectly states my notion about stratification and especially dead spots that pop up in the flow of circulation in my aquarium.

I like the way you have defined the difference between aquariums and nature but I don’t get why there are ‘few infamous rift lakes’. I take it infamous is a typo as ‘increasing CO2 will cause a decrease in O2’ is also a typo due to the late hour of your post.

Thanks for helping me out here I guess I need to consider the notion pressure and the role it plays in my aquarium.
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post #12 of 13 Old 06-18-2013, 01:52 PM
Molecules do not change in surface area. When talking about a liquid they can only change in volume and density the molecule is what it is. It is H2O the molecule can not change in surface area unless it stops being H2O. You are correct that cooler water molecules are moving slower. Temperature effects the activity of the molecules. When liquid or gas molecules are all bouncing around and colliding with each other having a good time, this is do to temperature effecting their energy. The more they bounce/faster they are moving the more they hit other molecules and the more those bounce. The result is they occupy more space. Lost of energy equals a loss of temperature equals less movement and water becomes more dense as more molecules can occupy the same space as before. Dry ice(solid CO2) is cold as $#!! because it has to be, it can not be that dense or take a solid form unless it has little energy. When Co2 dissolves in water there is interactive hydrogen bonding with the H2O molecules. The more bonds formed with H2O molecules around it the happier and more stable things are. The less bouncing around the more interactions H2O will have with CO2 and the higher the solubility. I'm still not entirely sure if that is completely correct or the only way temperature effects solubility.

They are infamous be cause they literally are infamous. The BBC and NGC both have documentaries on them if you are interested one is on youtube under 'killer lakes'. In the 80's Lake Nyos caused the sudden death of 1,700 people living in the lake basin and about twice as many livestock. This was due to a massive and violent release of CO2. Nyos is almost 700 feet deep, as mentioned previously colder the water and higher the pressure(deeper) the more CO2 water can hold. When a large disturbance occurs in water that is heavily saturated it can cause the gas to come out of solution in a chain reaction. The bubbles draw water up, suddenly CO2 rich water is being pulled towards less pressure and more CO2 is gassing out and more bubbles and so on and so on. This continues rapidly until the lake suddenly turns-overs with its lower layers coming to the surface and mixing with other layers which is not good nor normal and results in releasing much of the trapped CO2. CO2 being heavier then air the cloud of CO2 displaced all the oxygen around the lake leading to suffocation. These lakes are unique in this aspect and the only example I know of where excessive CO2 input occurs in nature.

.... I'm probably drunk.

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post #13 of 13 Old 06-19-2013, 11:22 AM Thread Starter
Hello Mikaila31;
I got caught with that remark about surface area changing but what I intended to say is that molecules have a relationship between surface area and density or mass. This is an inverse relation where surface area’s ratio to mass (density) decreases as density increases. Take a molecule where surface area has a value of 20 and a mass (density) value of 1 so the relationship of surface area to mass (density) is 20:1(20 values of surface area to 1 value mass (density)); using the same molecule with a surface area value of 20 and mass (density) value of 30 the surface area’s relationship to mass (density) will be reduced to a ratio of 2:3, giving much reduced surface area compared to mass.

I liked the story about energy and molecules bouncing around and you have brought us to an area I am not familiar with so my notions here are very weak.

I had forgotten about the killer lakes but as I read about them I remembered the story from back then, it just amazing what events nature and the earth provide. As to carbon dioxide being heavier than air taking all of those lives causes one to consider the danger that CO2 represents and I will be more respectful towards CO2 in the future. I am curious if the oxygen in the air at those lakes was actually displaced or was there such a level of CO2 in the air that respiration was not able to diffuse CO2 from the blood into the air therefore the blood was not able to uptake oxygen (osmosis) which is different than displaced oxygen. I am thinking about space craft or submarines where there can be an unlimited amount of oxygen but one will still be unable to breathe until the CO2 is scrubbed out of the air. This suggests to me that oxygen and carbon dioxide are two separate processes that are independent of each other, but work together providing balance and equilibrium between the separate processes resulting in harmony to the ecology.
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