Sublimation
7 Minutes
Sublimation explained for students, showing how solids like naphthalene balls and dry ice turn straight into gas. A science lesson in English.
- Why naphthalene balls disappear and leave a smell on clothes
- How dry ice sublimates into carbon dioxide gas in air and water
- Changing dry ice into a liquid using temperature and pressure
What this lesson teaches
Sublimation (padangamudal) is the process where a solid turns directly into a gas without melting into a liquid first. While common solids like ice cubes must first melt into water and then boil into gas, sublime substances change straight from solid to gas at normal room temperature and pressure.
How dry ice turns into gas
Dry ice is the solid form of carbon dioxide gas, created by cooling carbon dioxide inside a container to minus 78 degrees Celsius. At this freezing temperature, the attraction force between molecules is very strong, and they lack the kinetic energy to escape. When dry ice is placed in room air at 25 degrees Celsius and 1 atmospheric pressure, warmer air molecules collide with it. The carbon dioxide molecules absorb this heat energy, turn it into kinetic energy, and escape directly into gas as white smoke.
Why dry ice sublimates faster in water
- Dry ice placed in water at 25 degrees Celsius forms bubbles and turns into gas much faster than it does in air at the same temperature.
- Molecules in liquid water are packed much closer together than molecules in air.
- Because of this closer arrangement, water molecules collide with the dry ice much more frequently than air molecules do.
- These frequent collisions cause greater heat transfer to the dry ice, speeding up the sublimation process.
Why naphthalene balls disappear
Naphthalene balls are kept with clothes to prevent insects. At ordinary room temperature and pressure, the attraction force between naphthalene molecules is very weak. The molecules absorb heat from the surrounding air, which increases their kinetic energy and causes them to escape layer by layer as gas. As the solid ball gradually shrinks and disappears, some invisible molecules remain stuck to the fabric, which is why clothes keep the smell.
Turning sublime substances into liquid
- A substance that usually sublimates can be converted into a liquid under specific conditions.
- Dry ice can be turned into a liquid by applying a temperature of minus 56 degrees Celsius and 5 atmospheric pressure.
- Applying the appropriate temperature and pressure allows any subliming substance to enter the liquid state instead of skipping it.