The dominant area map is the most common and useful tool for summarizing the thermodynamic data of aqueous chemical systems. However, some of its limitations when drawing and applying it to the actual system also need to be considered.
The drawing of the dominant area map is limited by the adequacy of thermodynamic data. All possible substances in the system and the reactions between them should be considered. If one or more important substances are neglected, the result may be a completely misleading picture. For example, in the Fe-H 2 O dominance map, if the presence of Fe 2 + is neglected, the horizontal line separating the Fe 3 + and Fe 2 + regions disappears, and the line separating the Fe 3 + and Fe 2 O 3 regions extends to The boundary line of Fe 2 O 3 and Fe 3 O 4 then changes the slope to separate the Fe 3 + and Fe 3 O 4 regions.
The correctness of the map of the dominant area is also limited by how the thermodynamic data is selected. Some free energy data can be obtained from various standard sources, but for detailed studies, the data for solution components must be calculated from the stability constant of the reaction. The stability constant needs to be chosen very carefully based on reproducibility and similarity to the medium (ionic strength and electrolyte composition) of the system under study. In many cases the stability constant needs to be corrected for the ionic strength and the activity of the substances involved in the reaction, and these ionic strengths and activities may not be known. Therefore, the advantage zone map should be updated periodically based on new or more accurate data.
The free energy data of many solution materials at high temperatures is unknown. The most common way to solve a problem is to use the Crist-Cobble correspondence principle to estimate the entropy and indirectly obtain the free energy value. This method is considered feasible for four ions: simple cation simple anion, oxyanion and oxyacid anion. However, it does not apply to certain substances, such as coordination ions, uncharged substances, and multi-plant matter.
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