When a sealed can of soda is left in a hot car, many believe the container will violently explode. While containers can fail and rupture under extreme heat, the process is not a random, catastrophic explosion. The forces at work are predictable physical and chemical reactions governed by thermodynamics and gas behavior. Understanding whether a soda container truly “explodes” involves examining the pressurized system inside, how temperature affects the dissolved carbon dioxide (CO2), and the precise design limits of the container itself.
Carbonation: The Science of Dissolved Gas
A freshly sealed soda is a pressurized system engineered to keep a large amount of carbon dioxide (CO2) gas dissolved within the liquid. This relies on Henry’s Law, which states that the amount of gas dissolved is directly proportional to the partial pressure of that gas above the liquid. During manufacturing, the beverage is saturated with CO2 under high pressure, far exceeding normal atmospheric pressure. This forces CO2 molecules into the liquid, creating a supersaturated solution stable only while the container remains sealed. The small volume of gas in the headspace—the gap between the liquid and the lid—maintains this pressure equilibrium. In a typical chilled can, the gauge pressure hovers around 30 to 40 pounds per square inch (PSI), which gives the beverage its characteristic fizz and bite.
How Heat Turbocharges Internal Pressure
Introducing heat to a sealed soda container triggers two compounding effects that rapidly increase the internal pressure. The first is a reversal of the solubility equilibrium. Temperature directly affects how well the liquid holds dissolved gas; carbon dioxide becomes significantly less soluble as the liquid warms up. This causes CO2 molecules to escape the solution more quickly. The second effect is the thermal expansion of the gases already present in the headspace, described by Charles’s Law. Since the volume of the sealed container is fixed, an increase in temperature causes the gas molecules to move faster and collide with the container walls with greater frequency and force. Both the CO2 escaping the liquid and the increased kinetic energy of the existing gas molecules contribute to a drastic spike in the total internal pressure. For instance, a container heated from 40°F (4°C) to 130°F (54°C)—a temperature easily reached inside a car—can see its internal pressure nearly double.
Explosion vs. Rupture: Container Integrity
Whether a container fails catastrophically or simply ruptures depends heavily on its design and material. The term “explosion” implies fragmentation and a release of stored energy as a pressure wave, but manufacturers design modern beverage containers to prevent this. Aluminum cans are thin-walled pressure vessels engineered to hold the initial internal pressure but are also designed with weak points. Instead of fragmenting, a can is more likely to deform and fail along a seam or at the thinner top or bottom dome when the internal pressure exceeds its burst threshold. This controlled failure releases the pressure by tearing the metal or separating a seal, resulting in a forceful spray rather than a shrapnel-producing explosion. Plastic bottles, particularly two-liter sizes, are stronger, capable of holding up to 170 PSI or more before failure. Their failure mode is typically a stretching and eventual tear in the plastic or a failure of the screw-on cap, which acts as a venting mechanism. This managed failure results in a rupture, not a true explosion of the container itself.
Why Hot Soda Fizzes Over
The most common result of heat exposure is the massive geyser that erupts when a hot soda is opened, not container failure. This occurs because the elevated temperature has already forced a substantial amount of carbon dioxide out of the liquid solution, making the liquid highly supersaturated. When the container is opened, the abrupt drop in pressure from the sealed internal level to the surrounding atmospheric pressure instantly destabilizes the solution. This rapid pressure release causes the CO2 barely held in the liquid to rush out immediately. The gas quickly forms bubbles around microscopic imperfections on the container’s inner surface, known as nucleation sites. The combination of heat-induced supersaturation and sudden depressurization triggers a massive, simultaneous bubble formation. This rapid formation of gas bubbles creates foam, displacing the liquid volume and forcefully pushing the beverage out of the opening.