Gases in the sea Flashcards
What is equilibrium?
A dynamic state when there is a forward and back reaction occurring at the same rate and can occur across the water surface
What is true of oxygen equilibrium?
Oxygen in the air is at equilibrium with oxygen in the water
What is true of oxygen solubility?
Oxygen has quite low solubility and is constantly exchanging across the water surface
What is true of the solubility of gases in water?
- Some gases (e.g. O2, H2, N2, CH4) are often only slightly soluble and may be driven out by increased temperatures.
- Other gases chemically react with water to create a dissolved product (e.g. NH3, HCl, NO2)
What is true of ammonia’s solubility?
- Highly soluble
- Reacts to form ammonium ion
What is the link between the solubility of gas and its partial pressure?
The solubility of gas will increase with its partial pressure
What does Henry’s law state?
States that for some gases (O2, N2, CO2) the concentration in a solvent at a known temperature is proportional to partial pressure of the dissolving gas
c = K^H x p
where KH is Henry’s law constant
When is a liquid said to be saturated with gas?
A liquid is said to be saturated with a gas when it is at equilibrium with the gas above it
What are the controlling factors of gas saturation in a liquid?
- Partial pressure of gas
- Temperature
- Composition of liquid
Why can the liquid drift from the saturated condition?
A liquid can drift from the saturated condition as a result of uptake and loss of gas
What are the sources of dissolved oxygen in the sea?
- Diffusion from the atmosphere
- Photosynthesis
What is the key route of dissolved oxygen loss from seawater?
Respiration - e.g. by bacteria or larger organisms (zooplankton, fish, mammals, etc.)
Why might seawater become supersaturated with dissolved O2?
- Seawater warming quicker than O2 can diffuse out e.g. rockpools
- Photosynthesis occurring at a faster rate than O2 can diffuse out; more likely in calm, nutrient rich waters
What is the oxygen saturation in warm vs cold freshwater?
- Warm freshwater - ~7 mg L-1
- Cold freshwater - ~ 14mg L-1
What is the affect of salinity on oxygen saturation?
Salinity reduces the amount of oxygen which can be dissolved at saturation
What is the role of carbon dioxide?
- Carbon dioxide is produced by respiration and taken up for photosynthesis
- Also involved in buffering the sea water pH
Which gases are made in surface waters by biological processes?
- N2O
- CO
- CH4
-CH3I - so transfer from the sea to the air
Where is SO2 created?
- It is created in the atmosphere or released by volcanoes and so its transport is from air to sea
What is true of oxygen equilibrium?
- Oxygen in the air is at equilibrium with oxygen in the water
- Oxygen has quite low solubility and is constantly exchanging across the water surface§
