What is the boiling point of water?

Explanation

The boiling point of water is the temperature at which water changes completely from the liquid state to the gaseous state. Under normal atmospheric pressure at sea level, pure water boils at 100°C. This value is considered the standard boiling point and is commonly used in schools, laboratories, and scientific measurements.

When water reaches this temperature, it forms bubbles throughout the liquid. These bubbles rise to the surface and release steam, showing that the water is turning into vapor.

What Happens During Boiling

• Water molecules absorb heat energy when heated.
• The absorbed energy increases their speed of movement.
• At lower temperatures, molecules escape only from the surface (evaporation).
• At boiling point, molecules escape from anywhere inside the water.
• Bubbles form throughout the liquid and rise upward, releasing vapor.

This is why boiling is faster and more active than simple evaporation.

Boiling and Atmospheric Pressure

When Pressure Is Low

At high altitudes or hill stations, air pressure is lower. Because of this, water boils at a lower temperature (around 90–95°C). This is why cooking takes longer in mountainous regions.

When Pressure Is High

In a pressure cooker, pressure increases as steam gets trapped. The boiling point rises above 100°C, making food cook faster. This is a common example of how pressure affects boiling.

Effect of Impurities

When substances like salt, sugar, or minerals dissolve in water, the boiling point increases slightly. This effect is called boiling point elevation. For example, salty water takes longer to boil than pure water.

Difference Between Boiling and Evaporation

• Evaporation happens only at the surface and at any temperature.
• Boiling happens throughout the liquid and only at the boiling point.
• Evaporation is slow, while boiling is fast and energetic.

Important Points

• Standard boiling point of pure water: 100°C
• Boiling point varies with atmospheric pressure
• Lower pressure → lower boiling point
• Higher pressure → higher boiling point
• Impurities increase the boiling point
• Boiling happens when vapor pressure equals atmospheric pressure