What happens when co2 is heated

Answer 1

What happens to CO₂ when heated will ultimately depend on the pressure. You can look at a phase diagram for CO₂ and see exactly what happens at different pressures and temperature. If you are asking about heating CO₂ at standard atmospheric pressure (1 atm), you would see that below -78.5ºC it is a solid, and above that temperature it is a gas. At atmospheric pressure it does not exist as a liquid.

At a pressure of 5.11 atm, CO2 is a solid below -56.4ºC, then as you heat it, it becomes a liquid and then a gas.