Answer the following questions based on the p-T phase diagram of carbon dioxide as shown in the figure .
(i) At what temperature and pressure can the solid , liquid and vapour phases of `C0_(2)` co-exist in equilibrium?
(ii) What is the effect of decrease of pressure on the fusion and boiling point of `C0_(2)` ?
(iii) What are the critical temperature and pressure for `C0_(2)` ? what is their significance ?
(iv) Is `C0_(2)` solid , liquid, or gas at (a) `-70^(@)C `under 1 atm (b) `-60^(@)C` under 10 atm (c) `15^(@)C` under 56 atm ?

Answer

(i)`-56.6^(@)C, 5.11` atm (ii) both decrease (iii) `31.1^(@)C,73` atm (iv) (a)vapour (b)solid (c) liquid

Explanation

(i) At triple point (temperature =`-56.6^(@)C`) & (pressure = `5.11` atm ) , the solid , the liquid & the vapour phases of `CO_(2)` co-exist.
(ii) Fusion point & boiling point both decrease on decreasing pressure.
(iii) Critical temperature is `31.1 ^(@)C` and critical pressure is `73.0` atm. On temperature higher than critical temperature it can't be liquified.
(A) Vapour (B) Solid (C) liquid