solid melting point problem
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Asking for help from the physical chemistry experts in the forum, when I was collecting MSDS, I found that the boiling point of some solids is lower than its melting point. This does not mean that it sublimates more easily than melts. Why is this? Please give me some advice.
This post was last edited by Qingcheng Jun on 2022-4-20 11:14 You can understand it through the three-phase diagram of this substance. Taking water as an example, the area surrounded by BO273 in the diagram is the sublimation zone, which is in a low-pressure state below the melting point. Generally, the sublimation process used for metal purification requires a vacuum pump to maintain a vacuum state. High temperature and low pressure make sublimation easy. In the carbon dioxide diagram, the parallel line with the ordinate 1atm is connected. The point that intersects the curve is the boiling point (sublimation point). This point is to the left of the triple point, and the sublimation point is lower than the melting point. In the diagram of water, connecting the parallel line with the ordinate 1atm, the intersection point with the curve is approximately at point P, to the right of the triple point, so the boiling point is greater than the melting point.