At what temperature does liquid water reach its highest density?

Liquid water reaches its highest density at 4°C. This phenomenon occurs due to the unique molecular structure and hydrogen bonding of water. As water cools from higher temperatures, its molecules move closer together, increasing density. However, as it approaches 0°C, water begins to form a crystalline structure due to hydrogen bonding, which causes it to expand and lose density.

At 4°C, the balance between the kinetic energy of the water molecules and the attractive forces of hydrogen bonds results in the maximum packing of water molecules, leading to the highest density. This characteristic is crucial in various natural processes, such as ice formation on lakes, where the less dense ice floats on top of the water, allowing aquatic life to thrive beneath the ice in winter conditions.

Understanding this thermodynamic property is fundamental in hydrodynamics and environmental science, as it influences water's behavior in ecosystems and its physical characteristics in engineering applications.