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Solids Or Gases In Liquids And General Characteristics Of Physical Equilibria

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Solids Or Gases In Liquids And General Characteristics Of Physical Equilibria - Lesson Summary

When a physical process, like dissolution, is taking place, it is possible to achieve a state of equilibrium.

There are two types of dissolution - gas in liquids and solid in liquids.

Sugar in water is a classic example of solid in liquid equilibrium

Sugar is added to a glass of water and stirred. It dissolves, forming a sugar solution. Then, as more and more sugar is added, it initially dissolves, but eventually reaches a stage where no matter how long you wait or how vigorously you stir, the sugar does not dissolve. The solution thus obtained is said to be saturated at the given temperature.

In a saturated solution, a dynamic equilibrium exists between the solute particles in undissolved state and the solute particles in the solution.

The equilibrium involving the dissolution of gases in liquids:

At a given pressure, equilibrium exists between the gas molecules in the gaseous state and those in the dissolved state in the liquid.

This equilibrium is governed by Henry's Law

Henry's Law:

'The mass of a gas dissolved in a given amount of a liquid at any temperature is directly proportional to the pressure of the gas present in equilibrium with the liquid'.

All carbonated drinks are bottled under pressure to increase the solubility of carbon dioxide in the solution.

General Characteristics of Physical Equilibrium:

· At atmospheric pressure, a solid exists in equilibrium with a liquid only at one temperature,

· At a given temperature, vapour pressure remains constant for equilibrium.

· At a given temperature, solubility remains constant for the dissolution of solids in liquids

· At a given temperature, the concentration of a gas in a liquid is directly proportional to the pressure of the gas over the liquid.

· At a given temperature, equilibrium can only be achieved in a closed system.

· At equilibrium, both the opposing tendencies occur at the same rate, and hence, a dynamic yet stable status is established.

· At a given temperature, the attainment of equilibrium for a physical process is characterised by constant value of one of its parameters such as vapour pressure, melting point, solubility or concentration.

At equilibrium, all the measurable properties of the system remain constant.


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