caption: an open system a system is located in a co2
exif: {"Image DocumentName": "SPECIATION IN OPEN CO2-H2O SYSTEMS - I", "Image ImageDescription": "In an open system, the system is in contact with its surroundings and components such as CO2 can migrate in and out of the system. Therefore, the total carbonate concentration will not be constant. Let us consider a natural water open to the atmosphere, for which pCO2 = atm. We can calculate the concentration of H2CO3  directly from KCO2: Note that M H2CO3  is independent of pH! Many natural waters are actually closer to being open systems with respect to CO2, including, according to Kehew (2001), many ground waters. In an open system, CO2 is free to pass into or out of the system. Thus, there is no guarantee that the total inorganic carbon concentration will remain constant. In other words, we lose our mass-balance constraint on the system. On the other hand, open systems are generally in equilibrium with a CO2-containing atmosphere, which can, over short time scales, be considered to be relatively constant. We therefore gain a Henry\u2019s Law constraint as shown in this slide. If pCO2 is fixed, then the concentration of H2CO3  is fixed, independent of pH. However, just because the concentration of H2CO3  is fixed, this does not mean that the total carbonate concentration is fixed, because variable amounts of dissociated forms of carbonate, i.e., HCO3- and CO32- will be present depending on the pH. However, if we know the pH and the pCO2 for an open CO2-H2O system, we can calculate the concentrations of all relevant species in the system from the mass-action expressions. These mass-action expressions include the Henry\u2019s law constraint (KCO2) shown in this slide, the dissociation constants of carbonic acid (K1, K2) and the dissociation constant of water (Kw).", "Image XResolution": "37", "Image YResolution": "37", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}