Answer the following questions based on the P–T phase diagram of CO2: (a) CO2 at 1 atm pressure and temperature – 60 °C is compressed isothermally. Does it go through a liquid phase? (b) What happens when CO2 at 4 atm pressure is cooled from room temperature at constant pressure? (c) Describe qualitatively the changes in a given mass of solid CO2 at 10 atm pressure and temperature –65 °C as it is heated up to room temperature at constant pressure. (d) CO2 is heated to a temperature 70° C and compressed isothermally. What changes in its properties do you expect to observe? | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter



Q.17:- Answer the following questions based on the P–T phase diagram of CO2:
(a) CO2 at 1 atm pressure and temperature – 60 °C is compressed isothermally. Does it go through a liquid phase?
(b) What happens when CO2 at 4 atm pressure is cooled from room temperature at constant pressure?
(c) Describe qualitatively the changes in a given mass of solid CO2 at 10 atm pressure and temperature –65 °C as it is heated up to room temperature at constant pressure.
(d) CO2 is heated to a temperature 70° C and compressed isothermally. What changes in its properties do you expect to observe?

 

 

Answer:-

The Pphase diagram for COis shown in the following figure:

(a) Since the temprature -60° C lies to the left of 56.6° C on the curve i.e. lies in the region vapour and solid phase, so carbon dioxide will condense directly into the solid without becoming liquid.



(b) Since the pressure 4 atm is less than 5.11 atm the carbon dioxide will condense directly into solid without becoming liquid.

(c) When a solid COat 10 atm pressure and -65° C temprature is heated, it is first converted into liquid. A further increase in temprature brings it into the vapour phase. At P = 10 atm, if a horizontal 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 COat 10 atm.

(d) Since 70° C is higher than the critical temprature of CO2, so the COgas 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 from its perfect gas behaviour with the increase in pressure.