Question

Q1)Why do liquids have onle one free surface?

Q2)Why solid CaCl2 spreads on road in cold countries during winter season?

Q3)Why only specific solids like napthalene balls undergo sublimation?

Q4)Why cool sensation is observed when alcohol is poured on palm?

Answer 1

1) That's because the rest of the surfaces assume the shape of the container.
Check the definition of a liquid - a state of matter that is able to flow and occupies the shape of its confining container.

2) CaCl₂ is spread on roads in cold countries to decrease the melting point of ice. Addition of calcium chloride over the ice results in depression in the freezing point of the ice.
Calcium chloride dissociate into 3 ions.
CaCl₂ ----> Ca²⁺ + 2Cl^-
Ions formed interfere with the network of H₂O molecules in ice and causes depression in the freezing point due to which ice melts readily on addition of CaCl2

Depression in freezing point on addition of non volatile solute to liquid.
Addition of a non-volatile solute, in the pure liquid, the freezing point of the liquid is lowered as, the vapour pressure of the liquid is decreased, due to presence of non volatile solute particles at the surface of the liquid. Consequently, the vapour pressure of the solid phase of pure liquid will be lowered.

3)The vapor pressure of any substance increases as temperature rises. Solids too, not just liquids. Sublimation happens when the total pressure of the atmosphere is less than the vapor pressure of compound, and melting has not happened yet because it is not hot enough. Different compounds have different vapor pressures.

4) When they arepoured on the palm, they evaporate readily and for this change of state they take the energy from thepalm and we get a cooling sensation.