Water’s volume increases when it transitions from a liquid to a solid state, a behavior highly unusual among common substances. Most materials contract and become denser upon freezing. This unique property means a specific volume of liquid water will occupy a noticeably larger space once it turns to ice. For a starting volume of \(200 \text{ cm}^3\) of water, determining the final volume requires understanding the molecular structure of ice and applying density calculations. This examination explains the science behind this phenomenon and determines the exact volume of ice created from \(200 \text{ cm}^3\) of liquid water.
The Unique Molecular Structure of Ice
The expansion of water upon freezing results directly from the structure of the \(\text{H}_2\text{O}\) molecule and hydrogen bonding. A water molecule is composed of one oxygen atom bonded to two hydrogen atoms, forming a bent, polar geometry. This polarity allows molecules to attract one another through hydrogen bonds.
In the liquid state, these hydrogen bonds constantly form, break, and reform as the molecules move randomly and pack closely together. This motion allows liquid water to achieve its maximum density near four degrees Celsius.
As the temperature drops toward the freezing point, the kinetic energy of the molecules decreases, and the hydrogen bonds become stable and fixed. The molecules are forced into a highly ordered, three-dimensional crystalline lattice. This hexagonal structure holds the molecules further apart than they are in the liquid state, creating open spaces within the crystal.
Since the same mass is spread over a larger volume, the resulting ice is less dense than the liquid water from which it formed. This density difference is the physical mechanism responsible for the volume expansion. The density of ice is approximately nine percent lower than the density of liquid water.
Determining the Final Ice Volume
Determining the final volume of ice requires a calculation based on the principle of mass conservation. When water freezes, the mass remains constant, while only its volume and density change. The calculation starts by establishing the mass of the initial water volume using the formula: Mass = Density \(\times\) Volume.
The density of liquid water at its freezing point is approximately \(1.0 \text{ g/cm}^3\). Given the starting volume of \(200 \text{ cm}^3\), the mass of the water is \(1.0 \text{ g/cm}^3 \times 200 \text{ cm}^3\), equaling \(200 \text{ grams}\). This mass is conserved, meaning the resulting ice will also have a mass of \(200 \text{ grams}\).
The next step uses the density of ice to find the final volume using the rearranged formula: Volume = Mass / Density. The density of ice at zero degrees Celsius is approximately \(0.9167 \text{ g/cm}^3\). Plugging the known mass and density into the equation yields \(200 \text{ grams} / 0.9167 \text{ g/cm}^3\).
Performing this division reveals that the final volume of the ice is approximately \(218.18 \text{ cm}^3\). Comparing this to the initial volume of \(200 \text{ cm}^3\) shows an absolute increase of \(18.18 \text{ cm}^3\). This represents a percentage expansion of approximately nine percent.
Everyday Implications of Water’s Expansion
The fact that water expands by about nine percent when it freezes has observable consequences across natural and engineered systems.
Aquatic Ecosystems
A result of this density difference is that ice floats on liquid water, which significantly impacts aquatic ecosystems. Ice forms a layer on the surface of bodies of water, insulating the liquid beneath and preventing entire lakes and rivers from freezing solid during winter. This allows fish and other organisms to survive in the deeper, unfrozen water.
Frost Wedging and Geology
In geology, the volume expansion of water is a powerful agent of physical weathering, known as frost wedging. When water seeps into cracks in rocks, freezing and expansion exert immense pressure on the surrounding material. Repeated cycles of freezing and thawing cause these cracks to widen over time, breaking down rock formations and contributing to the shape of the landscape.
Engineering and Infrastructure Damage
Engineers must account for this property when designing infrastructure in cold climates, especially water-carrying systems. The force generated by the volume increase can easily exceed the structural limits of common materials, leading to significant damage. This explains why water pipes burst when the water inside them freezes. It is also a factor in the development of potholes and road damage as trapped water freezes beneath the pavement. Furthermore, the expansion explains why a sealed glass container filled completely with liquid and placed in a freezer will often crack or shatter.