What is dry ice & Why does it steam when wet?

Asked by: Billy Hopkinson

Answer

Dry ice is nothing more than Carbon Dioxide (CO₂) which has reached the temperature at which it turns into its solid state, or what we would more commonly call its frozen state.

Carbon Dioxide is an interesting material because, at normal atmospheric pressures, it has no liquid state. It can only obtain a liquid state under very high pressure in a containment vessel.

So, when you have a frozen chunk of carbon dioxide out in the open where you can see it, it will transform directly from its solid state to a gas state with no intermediate liquid state. This process is known as 'sublimation'.

Dry ice does not really need to be wet with water to give off visible vapor, it will freeze water vapor in the air near it producing visible vapor all by itself, however adding water will also add substantial heat which will cause the solid CO₂ to sublimate at a greatly accelerated rate thus producing much more visible vapor.
Answered by: Evan Edwards, Ohio