Examine an unopened bottle of soda from the outside.
Look at the liquid before you open the bottle. You will not see very many bubbles, if any. The closed bottle is keeping the solution of soda and gas at a high pressure. This high pressure makes the gas soluble in the soda solution. As soon as you open the bottle and release the pressure however, the gas molecules start to come out of the solution. Bubbles form, rise to the surface of the liquid, and leave the solution. The solubility decreases as the gas pressure goes down, and the soda will taste more and more “flat.”
