Question

 

Open the phase diagram for CO2 given in the introduction again. Use the phase diagram for CO2 in the interactive activity and determine which of the following statements are correct.

Check all that apply.

CO2 is a gas under normal conditions of temperature and pressure.

When the pressure is 1 atm, there is no temperature at which the liquid phase of CO2 exists.

All three phases of CO2 exist simultaneously at the triple point.

CO2 forms a supercritical fluid at temperatures less than 31 degree C.

When the pressure is 4 atm and the temperature is more than - 56.7ºC, CO2 exists as a solid.

Movement across boundary line BO corresponds to a phase change.

Answer 1

A. Normal conditions of temperature and pressure are \(25^{\circ} \mathrm{C}\) and \(1.01\) bar pressure. From the phase diagram of \(\mathrm{CO}_{2}\), the area at the intersection of \(25^{\circ} \mathrm{C}\) and \(1.01\) bar pressure comes under gaseous phase. So \(\mathrm{CO}_{2}\) is a gas.

B. Pr essure of \(1 \mathrm{~atm}=1.01\) bar. The pressure of \(1.01\) bar is below the triple point of the phase diagram. So there is no temperature at which the liquid phase exists.

C. All three phases exist simultaneously at the triple point. This is the definition of the triple point.

D. \(\mathrm{CO}_{2}\) forms a supercritical fluid above the temperature of \(31^{\circ} \mathrm{C}\). So this statement is false.

\(\mathrm{E}\). When the pressure is \(4 \mathrm{~atm}\) and temperature is more than \(-56.7 \mathrm{C}\), the phase diagram indicates a gaseous state. So this statement is false.

F. A boundary line indicates the differnce between two phases. So movement across a boundary line corresponds to a phase change.

So \(\mathrm{A}, \mathrm{B}, \mathrm{C}\), and \(\mathrm{F}\) are true statements.