Name and describe the phase change that occurs when solid carbon dioxide (dry ice) is placed in an open container at room temperature

If you put a lump of solid carbon dioxide (dry ice) in a paper cup or

on a paper plate on the kitchen counter, it gets smaller and smaller

and finally it just disappears, but you never see a puddle around it

like you would with regular ice!

Carbon dioxide has no liquid phase when the pressure on it is less than

about 5 times normal atmospheric pressure. So in the kind of pressure

that we like to live in, dry ice goes straight to gas when it melts. That kind

of behavior is called "sublimation", and we say that the dry ice "sublimes".

Every substance has some pressure limit like that. For water, it's 0.006 of

normal atmospheric pressure. At any pressure lower than that, liquid water

can't exist, and an ice cube sublimes ... it melts directly into water vapor

without a puddle.