Give the general characteristics of equilibrium involving physical processes.

Explanation

General characteristics of equilibria involving physical processes are
1. In the case of liquid `hArr` gas equilibrium, the vapour pressure of the liquid is constant at equilibrium at a particular temperature.
eg. `H_(2)O(l)hArrH_(2)O(g)`
Vapour pressure of water `PH_(2)O` is constant at a given temperature.
2. For solid `hArr` liquid equilibrium there is only one temperature at which two phases can co-exist at a particular pressure. This temperature is known as melting point.
eg.: `H_(2)O(s)hArrH_(2)O(l)`
Ice `hArr` water
exist at 273 K at 1.0 atmosphere. At the melting point the masses of the two phases remain constnat provided no exchange of heat takes place between the system and the surroundings.
3. For dissolution of solid in liquids, the solubility (concentration of solid solute in solution) is constant at a given temperature.
e.: Sugar (s) `hArr` Sugar (aq)
Concentration of sugar in solution is constant at a given temperature.
4. For dissolution of gases in liquids the concentration of a gas in liquid, at a given temperature, is directly proportional to the pressure of the gas over the liquid.
eg: `CO_(2)(g)hArrCO_(2)(aq)`
`CO_(2)(aq) alpha PCO_(2)` or `[CO_(2)g]`
or `([CO_(2)(aq)])/([CO_(2)(g)])` is constant at a given temperature.