Why water freezes at 0°C?

Water freezes at 0°C (32°F) because the Celsius scale was designed around the behavior of water. When water cools, its molecules slow down until they form a crystal structure we call ice. This phase change happens at a specific temperature under normal atmospheric pressure.

The Celsius scale and water

Anders Celsius based his temperature scale on two key reference points:

• 0°C – the freezing point of water
• 100°C – the boiling point of water

This made temperature easy to understand and compare in everyday life, science, and weather measurements.

Why water doesn’t always freeze at exactly 0°C

In real conditions, water doesn’t always freeze at exactly 0°C. It can behave differently when:

• It contains impurities like salt or minerals
• It is under higher or lower pressure
• It is extremely pure and becomes supercooled below 0°C

Despite these variations, 0°C remains the standard reference point for freezing in the Celsius scale.

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