Chemcal Equilibrium and Kinetics

Chemical Equilibrium

Solid−Liquid Equilibria

• A perfectly insulated thermos flask is taken in which ice and water are kept at 273 K and atmospheric pressure.

• Observation − There is no change of mass of ice and water. (Despite being at the boundary between ice and water, molecules from the liquid water collide against ice and adhere to it. Similarly, some molecules of ice also escape into the liquid phase.)

• Reason: At 273 K and atmospheric pressure, the rate of transfer of molecules from ice to water is equal to that of transfer of molecules from water to ice.

• This state is known as equilibrium state.

H₂O_(s) H₂O_(l)

• It may be noted that ice and water are in equilibrium only at particular temperature and pressure.

• Normal melting point or normal freezing point − Temperature at which the solid and liquid phases of the substance are at equilibrium at atmospheric pressure

• Conclusion:

• Both the opposing processes occur simultaneously.

• Both the processes occur at the same rate so that the amount of ice and water remains constant.

  Liquid-Vapour Equilibrium

• Experimental set up

• 

• Anhydrous CaCl₂ is taken for few hours.

• Anhydrous CaCl₂ is removed and a dish of water is quickly placed.

• Observation

• Mercury level in the right limb of the manometer slowly increases and attains a constant value. That is, pressure inside the box increases and reaches …