To determine the phase of carbon dioxide (CO2) at -70°C and 1 atm pressure, we would typically refer to a phase diagram for CO2. A phase diagram is a graphical representation of the physical states of a substance under different conditions of temperature and pressure.
Here's how we can understand the phase determination step-by-step:
1. Interpret the phase diagram:
- A phase diagram has regions that indicate whether a substance will be in a solid, liquid, or gas state under different conditions of temperature and pressure.
- For CO2, the diagram will have clearly demarcated regions showing where each phase (solid, liquid, gas) is most stable.
2. Locate -70°C on the temperature axis:
- Find -70°C on the horizontal axis of the phase diagram.
3. Locate 1 atm on the pressure axis:
- Find 1 atm on the vertical axis of the phase diagram.
4. Determine the phase boundary:
- Next, see where the temperature of -70°C intersects with the pressure of 1 atm on the phase diagram.
5. Identify the region:
- The intersection point (-70°C, 1 atm) will lie within one of the regions demarcated in the phase diagram. This will tell us whether CO2 is solid, liquid, or gas at these conditions.
Based on this process and the information given:
- At -70°C and 1 atm pressure, CO2 falls within the solid region on the phase diagram. Hence, at these conditions, carbon dioxide is in the solid phase.
Therefore, the correct answer is:
- D. It is in the solid phase.
