Changes of State of Matter
Like evaporation and condensation you see every day, and the weird ones like sublimation
Kids Talk Science
I'm melting, Marko!
Want me to turn on the AC?
You just don’t get it, do you?
Mark: You said you're melting. I know substances can change their state—usually when we heat or cool them. We do it all the time. To get ice, we put water in the freezer.
Sara: And when we boil water for tea, it turns into a gas called water vapor?
Mark: Exactly. We see substances change their state every day. And these changes have names: evaporation, condensation, melting, freezing…
Sara: Of course I know all that, Marko. Condensation, for example, happens when a gas becomes a liquid. Like when the warm air from our room hits the cold window in winter.
Mark: Right. We know those ones. But do you know what sublimation is?
Sara: Sublimation? Sounds familiar.
Mark: It’s when a substance goes straight from solid to gas. Kinda weird, right?
Sara: Wait, can that even happen? 😏
Mark: It can! Take iodine, for example. It's solid at room temperature, but when you heat it, it doesn't melt—it turns directly into a purple gas.
Sara: I love purple! You’ll show me someday, right? 😍
Mark: Promise.
Key Science Concepts
We’ve learned that substances can change state, and each type of change has a name. Sara says she understands it best when she draws how they’re connected—so she shared her diagram with us.
- Melting
- Changing from a solid to a liquid. Example – ice melting in a glass.
- Freezing
- Changing from a liquid to a solid. Example – water freezing into ice in the freezer.
- Evaporation
- Changing from a liquid to a gas. Example – boiling water in a kettle.
- Condensation
- Changing from a gas to a liquid. Example – water droplets forming on windows in winter.
- Sublimation
- Changing directly from a solid to a gas without melting first. Example – heating iodine to produce purple gas.
- Deposition
- Changing directly from a gas to a solid without becoming liquid first. Example – iodine gas turning back into solid crystals when cooled.
Science Fun Fact
There’s a gas that freezes by evaporating—it’s carbon dioxide (CO₂)! When CO₂ changes
from gas to solid at normal pressure, it skips the liquid phase. That’s sublimation!
But something really cool can happen: if gas CO₂ is cooled quickly, some of it can both sublimate and
condense at once. This makes a snowy fog made of tiny solid CO₂ particles. It looks like white smoke,
but it’s actually dry ice turning back into gas! That’s why dry ice is used in theaters
and concerts—to make fog that doesn’t leave any water behind.
Quick Science Quiz
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