Final answer:
Considering the phase diagram of CO2 and a pressure of 2 atm, no phase change occurs for carbon dioxide as it increases in temperature from -40°C to 80°C since it remains in the gaseous state throughout this temperature range.
Step-by-step explanation:
The question involves understanding the phase changes of carbon dioxide (CO2) with a change in temperature under a constant pressure of 2 atm. From the phase diagram of CO2, we know that the substance directly sublimes from a solid to a gas at 1 atm pressure without passing through a liquid phase. CO2 sublimes at a temperature of −78.5°C. However, at 2 atm and -40°C, CO2 is likely already in the gaseous state. As the temperature is increased to 80°C, there would be no phase change since it remains a gas throughout this range of temperatures at 2 atm pressure. Thus, the correct answer here, considering the specified conditions, would be that no phase change occurs.