Hygrometry
Saturated and unsaturated vapour.
Saturated vapour
Can't hold more liquid molecules at a given condition and does not follow gas law.
Unsaturated vapour
can hold more liquid molecules at the given conditions which follow gas laws.
Effect of volume on saturated vapour
The saturated vapour at given volume then on increasing volume it becomes unsaturated and on decreasing volume vapour remains saturated giving out more liquid molecules.
Effect of temperature on saturated vapour
When the temperature of saturated vapour increases then it becomes unsaturated and on decreasing temperature, it remains saturated giving out more liquid.
Effect of pressure
a. On melting point
1. Melting point of a body decreases on increasing pressure if volume decreases on melting E.g. ice
2. Melting point of the body increases on increasing pressure if volume increases on melting E.g. Wax.
b. On boiling point
Liquid boil if the total pressure on its surface becomes equal to the saturated vapour pressure so the boiling point increases on increasing pressure.
Triple point
The point on the P-T diagram at which 3 states of matter i.e. solid, liquid and gaseous state coexist, fusion curve, sublimation curve & vaporization curve meet. It is the standard point in thermometry since it is unique. Its value is 4.58mm of Hg pressure & 273.15k temperature for water and 5.11 atm pressure & - 56.6° C temperature for carbon dioxide.
Evaporation
The process of escaping liquid molecules from its surface by taking energy from surrounding molecules cooling is observed after evaporation and takes place at all temperature and stop if the vapour is saturated.
Humidity
The presence of water vapour in the air is called humidity. It is divided as
a. Absolute humidity
The mass of water vapour present in the unit volume of air is called absolute humidity.
