Thermodynamic vs Kinetic Control Forming Mercury(II) Iodide

On the left, dilute solutions of mercury(II) and iodide ions are mixed. The mixture immediately turns yellow, indicating the presence of yellow, rhombic mercury(II) iodide. Concentrated solutions of mercury(II) and iodide are in the beaker on the right. The concentrated mixture initially turns yellow, but almost immediately becomes bright orange, indicating the formation of the more thermodynamically stable orange, tetragonal mercury(II) iodide. Over time, the diluted solution turns from peach colored to bright orange, indicating a gradual transformation to tetragonal mercury(II) iodide.

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© 1997 Division of Chemical Education, Inc., American Chemical Society. All rights reserved.