Experiment:
i) Take around 100ml of water in a glass beaker and arrange it on a tripod stand with the burner below it.
ii) Suspend a thermometer in the beaker in such a way that the bulb is in contact with the water. A clamp stand could be used to hold the thermometer and shown in the diagram.
iii) Switch on the flame of the burner and keep checking the readings on the thermometer.
iv) Record the initial temperature when the water is just beginning to heat up.
v) Keep monitoring the temperature change in the thermometer while the water is heating up further.
vi) After a while, notice the vapours coming out of the boiling water. Record the temperature till half of the water has evaporated.
vii)Notice that the temperature in the thermometer will not rise above 100°C.
Diagrammatic Representation:
Explanation: The boiling point of water is the temperature at which the liquid water gets converted into its gaseous form of water vapour. The energy for this conversion is provided in the form of heat and is known as the latent heat of vaporisation.
As the temperature increases gradually, the water starts heating as the kinetic energy is increasing along with the rise in temperature. This rise in kinetic energy keeps on increasing the intermolecular space between the water molecules and they start to move about freely. At a certain temperature, the intermolecular space increases up to such an extent that the water molecules break free from each other and vaporise. This temperature is called the boiling point of water.
The temperature at which the water in the beaker was seen to evaporate is 100°C or 373.15K. This is the boiling point of water.
