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) No, as the temperature `-60^@C` lies to the left of `-56.6^@C` , carbon dioxide will condense to solid directly.
(b ) It condenses to solid directly without passing through the liquid phase.
( c) It turns to liquid phase and then to vapour phase. The fusion and boiling points are when the horizontal line on P-T diagram at constant pressure of 10 atm intersects the fusion and vaporisation curves.
(d) As `70^@C` is much higher than the critical temperature `CO_2` , will not exhibit any clear phase transition to liquid phase. It will remain in vapour phase but will depart more and more from ideal gas behaviour with increase in pressure.