at . bar pressure. For any pure liquid at one atmospheric pressure ( . bar), the temperature at which the liquid and vapours are at equilibrium is called normal boiling point of the liquid.
Boiling point of the liquid depends on the atmospheric pressure. It depends on the altitude of the place; at high altitude the boiling point decreases. . .
Solid – Vapour Equilibrium Let us now consider the systems where solids sublime to vapour phase. If we place solid iodine in a closed vessel, after sometime the vessel gets filled up with violet vapour and the intensity of colour increases with time. After certain time the intensity of colour becomes constant and at this stage equilibrium is attained. Hence solid iodine sublimes to give iodine vapour and the iodine vapour condenses to give solid iodine.
The equilibrium can be represented as, I (solid) I (vapour) Other examples showing this kind of equilibrium are, Camphor (solid) Camphor (vapour) NH Cl (solid) NH Cl (vapour) Fig. . Measuring equilibrium vapour pressure of water at a constant temperature . .
Equilibrium Involving Dissolution of Solid or Gases in Liquids Solids in liquids We know from our experience that we can dissolve only a limited amount of salt or sugar in a given amount of water at room temperature. If we make a thick sugar syrup solution by dissolving sugar at a higher temperature, sugar crystals separate out if we cool the syrup to the room temperature. We call it a saturated solution when no more of solute can be dissolved in it at a given temperature. The concentration of the solute in a saturated solution depends upon the temperature.
In a saturated solution, a dynamic equilibrium exits between the solute molecules in the solid state and in the solution: Sugar (solution) Sugar (solid), and the rate of dissolution of sugar = rate of crystallisation of sugar. Equality of the two rates and dynamic nature of equilibrium has been confirmed with the help of radioactive sugar. If we drop some radioactive sugar into saturated solution of non-radioactive sugar, then after