## 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 CO2 co-exist in equilibrium? (b) What is the effect of decrease of pressure on the fusion and boiling point of CO2? (c) What are the critical temperature and pressure for CO2? What is their significance? (d) Is CO2 solid, liquid or gas at (a) –70 °C under 1 atm, (b) –60° C under 10 atm, (c) 15 °C under 56 atm? | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter

### Q.16:- 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 CO2 co-exist in equilibrium? (b) What is the effect of decrease of pressure on the fusion and boiling point of CO2? (c) What are the critical temperature and pressure for CO2? What is their significance? (d) Is CO2 solid, liquid or gas at (a) –70 °C under 1 atm, (b) –60° C under 10 atm, (c) 15 °C under 56 atm?

Answer:-

The PT phase diagram for CO2 is shown in the following figure:

(a) The solid, liquid and vapour phase of carbon dioxide exist in equilibrium at the triple point, i.e., temprature = – 56.6° C and pressure = 5.11 atm.
(b) With the decrease in pressure, both the fusion and boiling point of carbon dioxide will decrease.
(c) For carbon dioxide, the critical temperature is 31.1° C and critical pressure is 73.0 atm. If the temprature of carbon dioxide is more than 31.1° C, it can not be liquified, however large pressure we may apply.
(d) Carbon dioxide will be (a) a vapour, at =70° C under 1atm. (b) a solid, at -6° C under 10 atm (c) a liquid, at 15° C under 56 atm.