What is sublimation curve ? With the help of this curve explain in which condition and how a solid can be directly converted to gas.

Looking at the phase diagram of carbon dioxide, Fig. 18.8 (b), answer the following questions :

 At what temperature and pressure can the solid, liquid and vapour phases of ${\mathrm{CO}}_2$ co-exist in equilibrium ?

Looking at the phase diagram of carbon dioxide, Fig. 18.8 (b), answer the following questions :

What is the effect of decrease of pressure on the fusion and boiling point of ${\mathrm{CO}}_2$?

Looking at the phase diagram of carbon dioxide, Fig. 18.8 (b), answer the following questions :

 (c) What are the critical temperature and pressure for ${\mathrm{CO}}_2$? What is their significance?

Looking at the phase diagram of carbon dioxide, Fig. 18.8 (b), answer the following questions :

 Is ${\mathrm{CO}}_2$ solid, liquid or gas at (i)$-70°\mathrm{C}$  under $1 \mathrm{atm}$ pressure, (ii) $-60°\mathrm{C}$ under $10$ atm pressure, (c) $15°\mathrm{C}$ under $15$ atm pressure ?

Looking at the phase diagram of carbon dioxide, Fig. 18.8 (b), answer the following questions :

${\mathrm{CO}}_2$ at $1$ atm pressure and temperature $-60°\mathrm{C}$ is compressed isothermally. Does it go through a liquid phase?

Looking at the phase diagram of carbon dioxide, Fig. 18.8 (b), answer the following questions :

 What happens when ${\mathrm{CO}}_2$ at $4$ atm pressure is cooled from room temperature at constant pressure ?

Looking at the phase diagram of carbon dioxide, Fig. 18.8 (b), answer the following questions :

Describe qualitatively the changes in a given mass of solid ${\mathrm{CO}}_2$ at $10 \mathrm{atm}$ pressure and temperature $-65°\mathrm{C}$ as it is heated up to room temperature at constant pressure.