What is sublimation and is it a physical or chemical change?

Sublimation is a physical change where a substance transitions directly from a solid to a gas, bypassing the liquid state.

Sublimation is a fascinating process that occurs when a substance changes its state from solid to gas without passing through the intermediate liquid phase. This is a physical change, not a chemical one, because the substance maintains its original properties throughout the process.

The process of sublimation is driven by temperature and pressure. When the temperature and pressure of a substance drop below its triple point (the specific temperature and pressure at which it can exist in all three states: solid, liquid, and gas), it can sublimate. This means that the particles in the solid phase have enough energy to overcome the forces of attraction between them and move directly into the gas phase.

A common example of sublimation is dry ice, which is solid carbon dioxide. When dry ice is exposed to room temperature, it doesn't melt into a liquid. Instead, it sublimates, turning directly into carbon dioxide gas. Another example is the process of freeze-drying, where water in food is frozen and then sublimated, removing the moisture and preserving the food.

Remember, sublimation is a physical change because it only involves a change in the state of the substance, not its chemical identity. The substance before and after sublimation is the same, only its form has changed. This is different from a chemical change, where a substance undergoes a reaction to become a new substance with different properties.