Describe the conditions necessary for sublimation to occur.
a) Low pressure and high temperature b) High pressure and high temperature c) Low pressure and low temperature d) High pressure and low temperature
The Correct Answer and Explanation is:
The correct answer is: a) Low pressure and high temperature.
Explanation:
Sublimation is the process in which a solid changes directly into a gas without passing through the liquid phase. This phenomenon occurs under specific conditions of temperature and pressure, which influence the phase transitions of a substance.
- Low Pressure: In order for sublimation to occur, the pressure must be low. At low pressures, the vapor pressure of the solid increases, meaning the molecules have a greater tendency to escape directly into the gas phase rather than staying in the solid phase or transitioning to liquid. At higher pressures, the solid may melt into a liquid instead of sublimating.
- High Temperature: High temperatures provide the energy required to break the bonds or intermolecular forces holding the molecules in the solid phase. This thermal energy increases the kinetic energy of the molecules, allowing them to overcome the forces that keep them in the solid state and transition directly into the gas phase. At lower temperatures, the molecules do not have enough energy to escape the solid structure.
These conditions—low pressure and high temperature—are typical of environments such as the surface of dry ice (solid CO₂). Dry ice sublimates at room temperature (high temperature) under low atmospheric pressure because CO₂ has a sublimation point that is below its melting and boiling points, allowing it to transition directly from solid to gas.
Examples of Sublimation:
- Dry Ice (solid CO₂): Sublimates at room temperature, turning directly into carbon dioxide gas.
- Iodine crystals: At higher temperatures, iodine undergoes sublimation, where purple iodine gas forms directly from the solid phase.
- Snow and ice: Under certain low-pressure, high-temperature conditions, snow and ice can sublimate directly into water vapor, particularly in dry or desert climates.
In summary, sublimation is favored by low pressure and high temperature, as these conditions allow solids to bypass the liquid phase and transform directly into gas.