Properties of Matter

Properties of Matter

Melting Point

The temperature at which solid and the liquid forms of the substance exist at equilibrium or both forms have same vapour pressure is called melting point. After adding impurities, the melting point decreases.

Boiling point

It is a temperature at which vapour pressure of a liquid becomes equal to atmospheric pressure and at which a substance converts from its liquid state to gaseous state. Atmospheric pressure usually decreases with height; hence, at high altitudes, the boiling point of the water is less than 100°C.

Freezing Point

The temperature at which the vapour pressure of its liquid is equal to the vapour pressure of the corresponding solid is called freezing point.

Evaporation

The process of conversion of a liquid into its vapours at room temperature is called evaporation. Evaporation causes cooling. Actually, during evaporation, the molecules having higher kinetic energy escape from the surface of the liquid. Therefore, average kinetic energy of (he rest of the molecules decreases. Therefore cooling takes place during evaporation because of temperature of liquid is directly proportional to average kinetic Energy.
Evaporation is affected by following factors :
(i) Nature of liquid
(ii) Temperature
(iii) Surface area.

Vapour pressure

(e) Vapour pressure The pressure exerted by the vapours of liquid in equilibrium with liquid at a given temperature is called vapour pressure. Vapour pressure depends upon —
(i) its nature
(ii) temperature.

Higher the vapour pressure of a particular liquid lesser will be the magnitude of intermolecular forces present in molecules. Vapour pressure of a liquid increases with increase in temperature.

Condensation

It is the process of conversion of gas into liquid. Solid, liquid, and gases are interconvertible by changing the condition of temperature and pressure.