The Unique Density of Water in Its Liquid State

The density of pure water changes under different conditions. At the temperature and pressure where ice transforms to liquid water, the density is approximately 917 kg/m3. This transformation occurs at 0°C (273.15 K) and 1 atm (101.325 kPa).

Roughly 1 Gram Per Milliliter

Water's density is often described as approximately 1 gram per milliliter (g/mL) or equivalently 1.0 g/cm3. However, this density can vary with temperature or the presence of dissolved substances. In its solid form, ice has a lower density than liquid water, making ice cubes float in a glass of water.

Water's Density Under Standard Conditions

Under standard conditions, water has a convenient density of 1.0 g/mL. For ice, the density is even lower. This unusual property is the reason why ice floats in water, as most materials become denser when they freeze.

Not All Substances Behave Like Water

For most substances, the solid phase is denser than the liquid phase. However, water is an exception. Liquid water is denser than ice. At 4°C, water reaches its maximum density, which then decreases as it approaches the freezing point. This phenomenon is not a universal one and is unique to water.

Expansion Upon Freezing

When water turns into ice, it expands, taking up more space. This expansion is significant, which is why ice floats on water. In colder conditions, water at 0°C will freeze from the top down, and ice will form on the surface of lakes and oceans.

The Importance of Specific Heat and Heat of Vaporization

Water is remarkable for its specific heat, which is the highest of any common substance. This means that 1 calorie per gram per degree Celsius is equivalent to 4.186 J/g°C. This property plays a crucial role in maintaining the temperature stability of land and living organisms, including humans, as well as making water an efficient coolant for various applications. The heat of vaporization of water, which is also higher than most substances, allows for effective cooling through evaporation, extending the range of temperatures in which humans can survive.

Standard for Density

Water serves as the standard for density, with 1 gram per cm3 being the accepted value. This standard is crucial for numerous scientific and practical applications, from engineering to biological research.

In conclusion, the density of water, its expansion upon freezing, and the specific heat and high heat of vaporization are unique properties that make water an essential and exceptional substance, unique in comparison to most other materials.