text: Sodas are carbonated, meaning that they have Carbon Dioxide gas dissolved in the liquid.  When a soda goes "flat", almost all the Carbon Dioxide has escaped.\n\nCarbon Dioxide is a gass at any normal pressure/temperature we would deal with soda at (refrigerator, store shelf, ...), and being a gas, its solubility in water depends greatly on two things, the temperature of the solution and the pressure above the solution.\nA lower temperature or higher pressure makes CO2 gas more soluble in water, thus it is always best to keep your botttles closes and in the refrigerator in order to keep the soda from going flat.\n\nThe carbon Dioxide gass dissolved in the water reaches an equilibrium with CO2 that has gotten out of solution and has become trapped inside the bottle above the liquid, when this happens, the amount of CO2 in solution is constant.  When you open the bottle and relieve the pressure above the liquid, the equilibrium is disturned and the gas dissolved in the liquid comes out of solution to try to re-establish the equilibrium.  That is why you see a bunch of bubbles when you open a soda bottle/can, it is the CO2 gas coming out of solution due to the decrease in pressure.