Equilibrium of Gases in Water

  1. Hi, first time poster. Here's the scenario. In a given vessel containing a given amount of water at a given temp, gases from the air will reach equilibrium with those dissolved in the water contained in the vessel. Now suppose live plants are added to the water. During the day, photosynthesis will occur, which will skew the relative ratio of O2 and CO2 in the water towards the O2. If while this is occurring, atmospheric air is diffused into the water via an airstone powered by an air pump, what will be the effect on the ratio of CO2 to O2? It seems obvious to me that under these circumstances that aerating the water will increase the level of CO2 dissolved in it, however marginally. Is this correct? Thanks!
  2. jcsd
  3. Borek

    Staff: Mentor

    Yes, but the exact final effect will depends on kinetics - how fast gases are produced and how fast gases are exchanged.
  4. Thanks for the quick reply!
  5. Ok one more question. All else being equal, wouldn't increasing levels of aeration push the ratio more strongly back towards equilibrium (in this case higher CO2 levels)through increasing the surface area of the air/water interface?
  6. Borek

    Staff: Mentor

    Once the speed of exchange is high enough, presence of plants/animals stops to matter, and the composition of dissolved gases is always the same (and in a simple equilibrium with those present in the atmosphere).
  7. My thoughts exactly sir. The water and air "want" to be at equilibrium with each other, and once equilibrium is reached no amount of air pumped through the water will change that equilibrium. Thank you again!
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