Final answer:
Sublimation is the direct transition of a substance from the solid to the gas phase, observed in materials such as dry ice and iodine, and is characterized by the enthalpy of sublimation. It is also used in vacuum sublimation to purify substances followed by melting point analysis to gauge purity.
Step-by-step explanation:
Sublimation is a process where a solid directly transitions into a gas without passing through the liquid state. This phenomenon can be observed in everyday life, such as when dry ice (solid CO2) produces fog-like smoke as it sublimes or when snow vanishes without melting. Some substances, such as iodine and naphthalene, undergo sublimation at room temperature, which can be demonstrated in a laboratory setting. The energy change associated with sublimation is called the enthalpy of sublimation (AHsub), which is the sum of the heat of fusion (AHfus) and the heat of vaporization (AHvap), as outlined by Hess's law.
Sublimation is not only a fascinating concept in phase changes, but it's also practical; it's used to purify solids in a process called vacuum sublimation. After sublimation, melting point analysis can confirm the purity of the product, as impurities typically lower the melting point and broaden the melting point range. The process of sublimation and the criteria for purity assessment are important basic tools for anyone studying or working in the field of chemistry.