Answer the following questions based on the P-T phase diagram of `CO_(2)` :
(a) `CO_(2)` at 1 atm pressure and temperature - `60^(@)C` is compressed isothermally. Does it go through a liquid phase ?
(b) What happens when `CO_(2)` at 4 atm pressure is cooled from room temperature at constant pressure ?
(c ) Describe qualitatively the changes in a given mass of solid `CO_(2)` at `10` atm pressure and temperature- `65^(@)C` as it is heated up to room temperature at constant pressure.
(d) `CO_(2)` is heated to a temperature`70^(@)C` and compressed isothermally. What changes in its properties do you expect to observe ?

Explanation

(a) Since the temp- `60^(@)C` lies to the left of `56.6^(@)C` on the curve i.e. lies in the region of vapour and solid phase. So `CO_(2)` will condense directly into solid with out becoming liquid.
(b) Since the pressure 4 atm is less than `5.11` atm. The carbondioxide will condenses directly into solid without becoming liquid.
(c ) When a solid `CO_(2)` at 10atm. Pressure and `-65^(@)C` temp is heated, it is first converted into a liquid. A further increase in temperature brings it to the vapour phase. At `P=10atm`. If a horizontal line is drawn parallel to the T-axis. Then the points of intersection of this line with the fusion and vapourisation curve will give the fusion and boiling point of `CO_(2)` at 10atm.
(d) Since `70^(@)C` is higher than the critical temperature of `CO_(2)`. So the `CO_(2)` gas on being compressed isothermally at `70^(@)C`. It will remain in the vapour state. Nowever the gas will depart more and more now its perfect gas behavious with the increase in pressure.