The boiling point of a liquid is the temperature at which its vapor pressure becomes equal to the external pressure (usually atmospheric pressure). At this point, bubbles of vapor form inside the liquid and rise to the surface.
Key points:
- Definition: The fixed temperature at which a liquid changes to gas (boils) throughout its bulk, not just at the surface.
- Normal boiling point: The boiling point measured at 1 atmosphere (760 mmHg) pressure.
- Effect of pressure:
- At higher pressure (like in a pressure cooker), the boiling point increases.
- At lower pressure (like on mountains), the boiling point decreases.
Examples:
- Water boils at 100 °C (373 K) at 1 atm pressure.
- At the top of Mount Everest, water boils at around 70 °C due to low air pressure.
Importance:
- Used in cooking (pressure cookers), distillation, and identifying substances.
In short: The boiling point is the temperature at which a liquid changes into vapor throughout its volume, when vapor pressure equals external pressure.