A sample of solid iodine is placed in a sealed flask and heated. The solid turns directly into a purple vapor without passing through the liquid phase. When the vapor is cooled, it deposits as solid iodine on the cooler walls of the flask. Which pair of terms correctly describes these two changes of state?
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Correct answer
B. Sublimation and deposition
Principle or equation
Sublimation is the direct transition from solid to gas; deposition is the direct transition from gas to solid.
Why this answer is correct
Iodine is a classic substance that sublimes at moderate heating. The solid to vapor change is sublimation; the vapor to solid change is deposition. Melting/freezing involve liquid, evaporation/boiling involve liquid to gas, condensation is gas to liquid.
Example
Dry ice (solid CO2) changes directly to CO2 gas at room temperature; frost forming from water vapor is deposition.
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