Heat and change of physical state - Concept of Boiling (Vaporization)

Boiling is the process where a liquid turns into vapour when it reaches a specific temperature called the boiling point. At this point, bubbles form throughout the liquid, and it changes to gas rapidly.

Water naturally evaporates all the time, even without heating. For example, when water is spilt on the floor, it dries up slowly because it evaporates from the surface. Evaporation occurs from the surface of the water, and it’s a slow process.

When water vapour (steam) cools, it turns into liquid water. This process is called condensation. Interestingly, condensation occurs at the same temperature as boiling-100°C. So, the temperature at which water boils and the temperature at which it condenses are the same.

1. Aim: To observe the boiling of water and determine its boiling point.

2. Requirements: beaker, water, burner or stove, tripod stand and wire gauze, and thermometer.

3. Procedure

• Take some water in a beaker and place it on a tripod stand.
• Insert a thermometer into the beaker without touching the bottom.
• Start heating the water using a burner.
• Note the temperature as bubbles begin to form.
• Continue heating until rapid boiling occurs and observe the temperature.

Boiling

4. Observation

• Small bubbles form at lower temperatures.
• As heating continues, water boils rapidly and bubbles rise from all parts of the liquid.
• The thermometer shows a constant temperature at 100°C during rapid boiling (at sea level).

5. Conclusion
Water boils at a fixed temperature known as the boiling point (100°C at sea level).
At this point, evaporation occurs throughout the liquid, not just at the surface.