Carbonated water, often called sparkling water or seltzer, is water infused with pressurized carbon dioxide (\(\text{CO}_2\)) gas. This process creates a solution of carbonic acid, which gives the water its characteristic fizz and tart taste. Introducing this dissolved gas fundamentally changes the physics and chemistry of the freezing process. Understanding what happens when this pressurized liquid is subjected to freezing temperatures reveals a complex interplay of solubility, volume expansion, and internal pressure.
How Cold Temperatures Affect Dissolved Carbon Dioxide
The presence of dissolved carbon dioxide causes the freezing point of the water to be slightly lower than that of pure water, a phenomenon known as freezing point depression. This means the carbonated water must reach a temperature below 0 degrees Celsius to begin solidifying. Gases are far less soluble in solids than they are in liquids. As the water molecules begin to align and crystallize into ice, the dissolved \(\text{CO}_2\) molecules are physically excluded from the solid structure. This exclusion forces the gas out of the liquid solution and back into its gaseous state. The gas is forced out of solution and collects in the remaining liquid volume or the container’s headspace, leading to a rapid increase in the number of free gas molecules.
Why Containers May Burst When Freezing Carbonated Water
The main safety concern and most dramatic outcome of freezing carbonated water in a sealed container is the significant pressure buildup that can cause the container to rupture. This pressure is generated by two distinct physical forces acting simultaneously.
Water Expansion
The first force is the expansion of water as it transitions into ice. Unlike most substances, water expands in volume when it freezes, increasing its volume by approximately 9%. In a rigid container, this volume increase creates immense internal stress on the container walls. This force alone is often enough to crack or split the vessel.
Gas Release
The second force is the sudden release of the dissolved carbon dioxide gas. As the water freezes and expels the \(\text{CO}_2\) molecules, the gas is pushed into the remaining liquid volume and the headspace. This gaseous \(\text{CO}_2\), now confined, causes a major spike in pressure. The combination of water expansion and gas pressure subjects the container to a much greater internal force than it was designed to withstand, leading to a high risk of rupture or explosion.
The Characteristics of Carbonated Water Ice
The resulting solid is not a clear, pristine block of ice like that made from regular water. Ice formed from carbonated water often has a white, cloudy, or opaque appearance. This visual characteristic is caused by the large volume of \(\text{CO}_2\) gas that was expelled from the solution and became trapped within the forming ice structure.
The texture of the ice is also notably different; it is typically more brittle, fragmented, and porous compared to standard ice. The trapped gas creates numerous tiny pockets throughout the ice matrix, which weakens the overall structural integrity.
If the frozen carbonated water is allowed to thaw, the resulting liquid will be noticeably flat. Since the freezing process forced the \(\text{CO}_2\) out of the solution, the carbonation is lost to the atmosphere when the container is opened. In carbonated soft drinks, freezing can cause water to freeze first, concentrating the sweeteners and flavorings in the remaining liquid, which can lead to an uneven flavor profile in the final thawed beverage.