Explain the process of melting of ice with explanation of freezing, melting and melting point.

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 sıgnificance ?

$(d)$ Is $CO _{2}$ solid, liquid or gas at $(a)\;-70\,^{\circ} C$ under $1\; atm$, $( b )\;-60\,^{\circ} C$ under $10 \;atm,$ $(c)$ $15\,^{\circ} C$ under $56$ atm ?

A thermally insulted vessel contains $150\, g$ of water at $0\,^oC$. Then the air from the vessel is pumped out a adiabatically. A fraction of water turns into ice and the rest evaporates at $0\,^oC$ itself. The mass of evaporated water will be closes to ……. $g$ (Latent heat of vaporization of water $= 2.10 \times10^6\, Jkg^{-1}$ and Laten heat of Fusion of water $ = 3.36 \times10^5\,Jkg^{-1}$ )

What is sublimation ? Give name of sublimation substances.

A closed bottle containing water at $30^{\circ} C$ is open on the surface of the moon. Then,