Answer the following questions based on the P-T phase diagram of carbon dioxide :
(a) At what temperature and pressure can the solid, liquid and vapour phases of `CO_(2)` co-exist in equilibrium ?
(b) What is the effect of decrease of pressure on the fusion and boiling point of `CO_(2)` ?
(c ) What are the critical temperature and pressure for `CO_(2)` ? What is their siginificance ?
(d) Is `CO_(2)` solid liquid or gas `70^(@)C` under1 atm, (b)-`60^(C)` under `10` atm, (c ) `15^(@)C` under 56 atm ?

Explanation

(a) The solid liquid and vapour phase of carbon dioxide exist in equilibrium at the point i.e., temperature `=-56.6^(@)C` and pressure `=5.11`atm.
(b) With the decrease in pressure both the fusion and boiling point of carbondioxide will decrease.
(c ) For carbondioxide the critical temperature is `31.1^(@)C` and critical pressure is `73.0` atm. If the temp of `CO_(2)` is more than `31.1^(@)C`. It cannot be liquified however large pressure we may apply.
(d) Carbondioxide will be (a) a vapour at - `70^(@)C` under 1 atm (b) a solid at `6^(@)C` under 10 atm (c ) a liquid at `15^(@)C` under 56 atm.