High School Physical Science: Matter and Change - Sublimation

Concept Summary

• Sublimation is the transition of a substance from the solid to the gas phase without going through the liquid phase.
• This process occurs when the intermolecular forces between the molecules of the substance are weak, allowing the molecules to escape into the gas phase directly.
• Sublimation is an endothermic process, requiring energy to break the bonds between the molecules.
• Sublimation is a common phenomenon in nature, observed in substances such as dry ice (solid carbon dioxide), iodine, and naphthalene.
• The rate of sublimation is influenced by factors such as temperature, pressure, and the surface area of the substance.

Questions

WHAT (definitional)

1. What is sublimation?
2. Answer: Sublimation is the transition of a substance from the solid to the gas phase without going through the liquid phase.
3. Real-world example: Dry ice, the solid form of carbon dioxide, sublimates at room temperature, producing a gas that can be seen as a white fog.
4. Misconception cleared: Sublimation is not the same as evaporation, which involves the transition from liquid to gas.
5. What are the conditions necessary for sublimation to occur?
6. Answer: Sublimation occurs when the intermolecular forces between the molecules of the substance are weak, allowing the molecules to escape into the gas phase directly.
7. Real-world example: Iodine crystals sublimate when heated, producing a purple gas.
8. Misconception cleared: Sublimation does not require the substance to be heated to a high temperature; it can occur at room temperature if the intermolecular forces are weak enough.
9. What is the energy requirement for sublimation?
10. Answer: Sublimation is an endothermic process, requiring energy to break the bonds between the molecules.
11. Real-world example: The energy required for sublimation can be provided by heating the substance or by increasing the temperature of the surroundings.
12. Misconception cleared: Sublimation is not an exothermic process, releasing energy as it occurs.

WHY (causal reasoning)

1. Why does sublimation occur in some substances but not others?
2. Answer: Sublimation occurs in substances with weak intermolecular forces, allowing the molecules to escape into the gas phase directly.
3. Real-world example: Iodine crystals sublimate because the intermolecular forces between the molecules are weak, allowing them to escape into the gas phase.
4. Misconception cleared: Sublimation is not solely dependent on the temperature of the substance; the strength of the intermolecular forces also plays a crucial role.
5. Why is sublimation an important process in nature?
6. Answer: Sublimation is an important process in nature because it allows substances to change phase without going through the liquid phase, which can be energetically favorable.
7. Real-world example: The sublimation of dry ice is an important process in the Earth's atmosphere, contributing to the formation of clouds and precipitation.
8. Misconception cleared: Sublimation is not just a laboratory phenomenon; it occurs naturally in many substances and plays a crucial role in the Earth's climate system.
9. Why is the rate of sublimation influenced by temperature and pressure?
10. Answer: The rate of sublimation is influenced by temperature and pressure because these factors affect the intermolecular forces between the molecules and the energy available for the process.
11. Real-world example: The rate of sublimation of iodine crystals increases with temperature and decreases with pressure.
12. Misconception cleared: The rate of sublimation is not solely dependent on the temperature of the substance; pressure also plays a crucial role in determining the rate of sublimation.

HOW (process/application)

1. How can sublimation be used in industrial applications?
2. Answer: Sublimation can be used in industrial applications such as the production of dry ice for cooling and the manufacture of iodine crystals for use in photography.
3. Real-world example: Dry ice is used in the food industry to keep food cold during transportation and storage.
4. Misconception cleared: Sublimation is not just a laboratory phenomenon; it has many practical applications in industry and everyday life.
5. How can the rate of sublimation be controlled?
6. Answer: The rate of sublimation can be controlled by adjusting the temperature and pressure of the surroundings.
7. Real-world example: The rate of sublimation of iodine crystals can be controlled by adjusting the temperature and pressure of the container.
8. Misconception cleared: The rate of sublimation is not solely dependent on the temperature of the substance; pressure also plays a crucial role in determining the rate of sublimation.
9. How can sublimation be used to purify substances?
10. Answer: Sublimation can be used to purify substances by allowing the impurities to remain in the solid phase while the pure substance sublimes.
11. Real-world example: Iodine crystals can be purified by sublimation, allowing the pure substance to be collected and used in applications such as photography.
12. Misconception cleared: Sublimation is not just a laboratory phenomenon; it has many practical applications in the purification of substances.

CAN (possibility/conditions)

1. Can sublimation occur at room temperature?
2. Answer: Yes, sublimation can occur at room temperature if the intermolecular forces between the molecules of the substance are weak enough.
3. Real-world example: Iodine crystals sublimate at room temperature, producing a purple gas.
4. Misconception cleared: Sublimation does not require the substance to be heated to a high temperature; it can occur at room temperature if the intermolecular forces are weak enough.
5. Can sublimation be used to separate mixtures?
6. Answer: Yes, sublimation can be used to separate mixtures by allowing the components to sublime at different rates.
7. Real-world example: Iodine crystals can be separated from other substances by sublimation, allowing the pure substance to be collected and used in applications such as photography.
8. Misconception cleared: Sublimation is not just a laboratory phenomenon; it has many practical applications in the separation of mixtures.
9. Can sublimation be used to store substances?
10. Answer: Yes, sublimation can be used to store substances by allowing them to sublime and re-solidify, reducing the risk of contamination and spoilage.
11. Real-world example: Dry ice is used to store food and other substances by allowing them to sublime and re-solidify, reducing the risk of contamination and spoilage.
12. Misconception cleared: Sublimation is not just a laboratory phenomenon; it has many practical applications in the storage of substances.

TRUE/FALSE (misconception testing)

1. Statement: Sublimation is an exothermic process.
2. Answer: FALSE
3. Real-world example: Sublimation is an endothermic process, requiring energy to break the bonds between the molecules.
4. Misconception cleared: Sublimation is not an exothermic process, releasing energy as it occurs.
5. Statement: Sublimation only occurs at high temperatures.
6. Answer: FALSE
7. Real-world example: Sublimation can occur at room temperature if the intermolecular forces between the molecules of the substance are weak enough.
8. Misconception cleared: Sublimation does not require the substance to be heated to a high temperature; it can occur at room temperature if the intermolecular forces are weak enough.
9. Statement: Sublimation is not an important process in nature.
10. Answer: FALSE
11. Real-world example: The sublimation of dry ice is an important process in the Earth's atmosphere, contributing to the formation of clouds and precipitation.
12. Misconception cleared: Sublimation is an important process in nature, allowing substances to change phase without going through the liquid phase, which can be energetically favorable.