Fizzing, scientifically known as effervescence, is the rapid formation and release of gas bubbles when a substance interacts with water or another liquid. This bubbly action results from gas escaping the liquid solution. This occurs through one of two primary mechanisms: the physical release of gas already dissolved in the liquid, or the chemical generation of a new gas through a reaction.
The Science of Gas Release
The foundational element in most common fizzing is Carbon Dioxide (\(\text{CO}_2\)). Water molecules naturally form a network of hydrogen bonds, and for a gas to dissolve, its molecules must fit into the spaces within this network. When a liquid is saturated with a gas, the system is in equilibrium, where the rate of gas molecules dissolving equals the rate of them escaping.
Fizzing begins when this equilibrium is disrupted, causing the dissolved gas to form bubbles and escape, a process called nucleation. Pure water can hold a gas in a state of supersaturation, meaning it holds more gas than it normally should at a given pressure and temperature. However, the energy required to spontaneously create a bubble from scratch is very high.
Bubbles rarely form randomly in the liquid itself. Instead, dissolved gas molecules gather at a “nucleation site,” which acts as a starting point. These sites are tiny imperfections, such as scratches on a glass or microscopic impurities suspended in the liquid. These rough surfaces allow gas molecules to cluster and form a bubble large enough to float to the surface.
Physical Fizzing: Releasing Dissolved Gas
Physical fizzing occurs when a gas is deliberately dissolved into a liquid under high pressure, a process called carbonation. Carbonated beverages, such as soda and seltzer water, are the clearest examples of this mechanism. The gas, usually \(\text{CO}_2\), is forced into the liquid at a pressure much higher than the surrounding atmosphere. This high pressure forces more gas molecules to remain dissolved than would naturally be possible.
The solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid. When a sealed bottle of soda is opened, the pressure above the liquid immediately drops to atmospheric pressure. This sudden decrease in external pressure drastically reduces the amount of \(\text{CO}_2\) the water can hold. The excess dissolved gas rapidly comes out of solution.
Temperature also plays a significant role in this physical process; gas solubility decreases as the liquid’s temperature increases. A warm soda will lose its fizz much faster than a cold one because the increased thermal energy makes it easier for the gas molecules to escape the water’s molecular network. The combination of reduced pressure and higher temperature accelerates the formation of bubbles at nucleation sites, producing the characteristic rush of fizz.
Chemical Fizzing: Generating Gas through Reaction
The second primary method of fizzing involves a chemical reaction that actively generates a gas upon contact with water. This mechanism is common in products like effervescent tablets, bath bombs, and certain cleaning powders. These products contain two main components that are stable when dry but react vigorously once dissolved in water: a solid acid and a solid carbonate or bicarbonate compound.
The most common reactants are a powder containing a bicarbonate, such as sodium bicarbonate, and a solid organic acid, like citric acid or tartaric acid. When the tablet or powder is dropped into water, the water acts as a solvent, dissolving the solid acid and the bicarbonate. Once dissolved, the acid releases positively charged hydrogen ions, and the bicarbonate releases negatively charged bicarbonate ions.
These ions then react in the solution, resulting in the formation of water and Carbon Dioxide gas (\(\text{CO}_2\)). This new gas is created within the liquid, causing it to become highly supersaturated almost instantly. The \(\text{CO}_2\) molecules quickly cluster together to form the bubbles that produce the visible fizzing. This acid-base reaction is efficient at generating gas, which is why effervescent tablets dissolve quickly.