Using the phase diagram for CO2, what phase is carbon dioxide in at -70°C and 1 atm pressure?

A. It is in the liquid phase.

B. It is in the solid phase.

C. It is at its melting point.

D. It is in the gas phase.

A

Explanation:

The Phase Diagram of Carbon Dioxide

At 1 atm, therefore, solid CO2 sublimes directly to the vapor while maintaining a temperature of −78.5°C, the normal sublimation temperature. Solid CO2 is generally known as dry ice because it is a cold solid with no liquid phase observed when it is warmed.