The maximum density of water occurs at approximately 277 K (4°C).
Explanation:
Water's behavior is unusual compared to most liquids. Instead of continuously increasing in density as it cools towards its freezing point, water reaches its maximum density at approximately 4°C (277 K). This phenomenon is due to the unique hydrogen bonding structure of water molecules.
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Hydrogen Bonding: Water molecules are polar, meaning they have a slightly positive end (hydrogen atoms) and a slightly negative end (oxygen atom). This allows water molecules to form hydrogen bonds with each other.
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Structure at Lower Temperatures: As water cools towards its freezing point (0°C or 273.15 K), the hydrogen bonds become more rigid, forming a crystal-like lattice structure. This structure increases the spacing between water molecules, thus decreasing the density. This is why ice is less dense than liquid water.
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Maximum Density Point: At 4°C (277 K), there's a balance between the decreasing thermal motion of the water molecules (which tends to increase density) and the increasing formation of ice-like structures (which tends to decrease density). At this specific temperature, the balance results in the highest possible density for liquid water. Above and below this temperature, water is less dense.
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Impact of Temperature Changes: As the temperature increases from 277 K (4°C), the clusters begin to deform and break, but the density is already decreasing because the thermal expansion dominates.
| Temperature (°C) | Temperature (K) | Density (kg/m³) |
|---|---|---|
| 0 | 273.15 | 999.84 |
| 4 | 277.15 | 999.97 |
| 10 | 283.15 | 999.70 |
| 20 | 293.15 | 998.20 |
Importance:
This property of water is crucial for aquatic life. During winter, the surface water cools and eventually freezes, but the water at the bottom of lakes and rivers remains at around 4°C, allowing aquatic organisms to survive.
