Answer the following question beased on tbhe 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 is equilibrium ? (b) What is the effect of decrease of pressure on the fusion and bolling point of `CO_2` ? (c ) What are the critical temperature and pressure for `CO_2` ? What is their significane ? (d) Is `CO_2` solid, liquid or gas at (a) ` -70^@C` under 1 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 triple point, i.e., temperature `= -56^@C` and pressure =5.11 atm. (b) With the decreases in pressure, both the fusion and boling point of carbon dioxide will decrease. (c ) For carbon dioxide, the critical temperature is `31.1^@C` critical pressure is 73.0 atm. If the temperature of carbon dioxide is more then `31.1 ^@C,` it can not be liquifend howsoever large pressure we may pressure we mat apply. (d) Carbon dioxide 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.