(a) Give two characteristic features of boiling (b) What will be the effect of the following on the boiling point of water: (i) addition of crystals of sodi...

(a) Two characteristic features of boiling: it takes place at a definite, fixed temperature (the boiling point) for a given external pressure, and the temperature stays constant while boiling continues; bubbles of vapour form and rise throughout the whole (bulk) of the liquid.

(b) Effect on the boiling point of water:

• (i) Addition of sodium chloride crystals: the boiling point is raised (the dissolved salt causes an elevation of boiling point).
• (ii) Reduction of the atmospheric pressure: the boiling point is lowered (water boils at a lower temperature when the pressure above it is reduced).

(c) Two ways boiling differs from evaporation: boiling occurs only at a fixed temperature (the boiling point), whereas evaporation occurs at all temperatures below the boiling point; boiling takes place throughout the whole body of the liquid (with bubble formation), whereas evaporation takes place only at the surface of the liquid.