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 temperature ` -60^@V` lies to the left of `56.6^@C` on the curve i.e. lies in the region of vapour and solid phase, so carbon dioxide will condens directily into solid without becoming liquid. (b) Since the pressure 4 atm. Is less then 5.11 atm. the carbon dioxide will condense directly into solid without becoming liquid. (c ) When a solid `CO_2` at 10 atm. pressure and `-65^@C` temperature is heated it is first converted into a liquid. A further increases in temperature brings it into the vapour phase. At = P = 10 atm, if a horzontal line is drawn parallel to the T -axis , then the points of intersection of this line with the fusion and vaporization curve will give the fusion and boiling points of `CO_2` at 10 atm. (d) Since `70^@C` is higher then the critical temperature of `CO_2`, so the `CO_2` gas can not be converted into liquid state on being compressed isothermally at `70^@C` it will remain in the vapour state. However, the gas will depart more and more form its perfect gas behaviour with the increase in pressure.