Difference between revisions of "How much of a solid will form?"
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Let's start off with 0.01 mole/Kg of CaCO<sub>3</sub> in 1 Kg of H<sub>2</sub>O at the aforementioned temperature and pressure. The OLI software initially assumes that no solids are present in the solution. We would have a solution concentration consisting of the following: | Let's start off with 0.01 mole/Kg of CaCO<sub>3</sub> in 1 Kg of H<sub>2</sub>O at the aforementioned temperature and pressure. The OLI software initially assumes that no solids are present in the solution. We would have a solution concentration consisting of the following: | ||
| − | {| | + | {| class="wikitable" |
| | | | ||
|Aqueous | |Aqueous | ||
| Line 32: | Line 32: | ||
|9.62E-06 | |9.62E-06 | ||
|---- | |---- | ||
| − | | | + | |CO<sub>2</sub> |
|2.25E-08 | |2.25E-08 | ||
|---- | |---- | ||
| − | | | + | |CO<sub>3</sub><sup>-2</sup> |
|1.25E-03 | |1.25E-03 | ||
|---- | |---- | ||
| − | | | + | |HCO<sub>3</sub><sup>-1</sup> |
|4.74E-04 | |4.74E-04 | ||
|---- | |---- | ||
|} | |} | ||
| + | |||
| + | The scaling tendency for CaCO<sub>3</sub> is calculated to be 428.4. The scaling tendency is the ratio of available ions in solution to the thermodynamic limit (also known as the K<sub>SP</sub>. The K<sub>SP</sub> is related the equilibrium equation. For CaCO<sub>3</sub> we have: | ||
| + | |||
| + | CaCO<sub>3(s)</sub> = Ca<sup>+2</sup> + CO<sub>3</sub><sup>-2</sup> | ||
| + | |||
| + | |||
| + | In short-hand form the Scaling Tendency would be | ||
| + | |||
| + | Scaling Tendency = [Ca<sup>+2</sup>][CO<sub>3</sub><sup>-2</sup>] / K<sub>SP</sub> | ||
| + | |||
| + | The K<sub>SP</sub> value is either obtained from thermodynamic values such as the Gibb's Free Energy of Reaction or from solubility experiments. | ||
| + | |||
| + | When the Scaling Tendency (ST) < 1.0 we say that the solid is under-saturated. When the ST > 1.0 the solid is said to be super-saturated. When the ST = 1.0 exactly, we say that the solid is saturated. | ||
| + | |||
| + | In this example, the ST = 428.4 which means that the solution is super-saturated with respect to CaCO<sub>3(s)</sub> | ||
Revision as of 11:38, 12 January 2015
How does the OLI Software determine how much solid will form?
To begin this discussion we will assume we have a simple solution of CaCO3 and H2O at 25 oC and 1 atmosphere. In addition we will ignore the activity coefficients to make the discussion simpler.
Let's start off with 0.01 mole/Kg of CaCO3 in 1 Kg of H2O at the aforementioned temperature and pressure. The OLI software initially assumes that no solids are present in the solution. We would have a solution concentration consisting of the following:
| Aqueous | |
| mol/Kg | |
| H+1 | 2.56E-11 |
| OH-1/ | 4.71E-04 |
| CaCO3 | 8.27E-03 |
| CaHCO3+1 | 6.75E-06 |
| Ca+2 | 1.71E-03 |
| Ca(OH)+1 | 9.62E-06 |
| CO2 | 2.25E-08 |
| CO3-2 | 1.25E-03 |
| HCO3-1 | 4.74E-04 |
The scaling tendency for CaCO3 is calculated to be 428.4. The scaling tendency is the ratio of available ions in solution to the thermodynamic limit (also known as the KSP. The KSP is related the equilibrium equation. For CaCO3 we have:
CaCO3(s) = Ca+2 + CO3-2
In short-hand form the Scaling Tendency would be
Scaling Tendency = [Ca+2][CO3-2] / KSP
The KSP value is either obtained from thermodynamic values such as the Gibb's Free Energy of Reaction or from solubility experiments.
When the Scaling Tendency (ST) < 1.0 we say that the solid is under-saturated. When the ST > 1.0 the solid is said to be super-saturated. When the ST = 1.0 exactly, we say that the solid is saturated.
In this example, the ST = 428.4 which means that the solution is super-saturated with respect to CaCO3(s)
