Carbon Speciation in a Closed System
In a closed system, we can more specifically analyze the relative concentration of each species. Since a closed system cannot lose molecules from solution, the total concentration of all species of a molecule (CT) must remain constant, even if relative amounts of species differ.
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Since equation 15 must remain a constant value in a closed system, we can consider the percent relationship between the three concentrations. For carbonic acid, this relationship is
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By substituting equations 12-14 into equation 16, we can further simplify it:

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