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Q & A: Boiling points of liquids and solids

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Most recent answer: 10/22/2007
Q:
Is the boiling point of a material which is liquid at room temperature (specifically H2O) less than the boiling point of a material which is solid at room temperature (specifically PbI2)?
- Anonymous
A:

Water is a liquid at room temperature and boils at 100 °C. Lead di-iodide is a solid at room temperature. It melts at 402 °C and boils at 954 °C. In this case, the substance which is a liquid at room temperature has a lower boiling point than the substance which is a solid at room temperature.

This is not a general rule, however. For example, mercury is a liquid at room temperature, with a melting point of -38.87 °C. Mercury boils at 357 °C. On the other hand, mercury bromide, HgBr2, is a solid at room temperature with a melting point of 236 °C, and a boiling point of 322 °C, which is less than that of pure mercury.

A warning, however. All of these materials (except water) are poisonous. Boiling them makes them even more dangerous because of the poisonous vapors released. Fortunately, melting and boiling points can be found tabulated in books.

The melting and boiling temperatures here come from the CRC Handbook of Chemistry and Physics.

Tom


(published on 10/22/2007)

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