* Exothermic reactions release heat. The formation of bubbles in soda is actually an example of a physical change, not a chemical change.
* Physical changes involve a change in state or form, not a change in chemical composition. The bubbles in soda are formed by the release of dissolved carbon dioxide gas. This is driven by a decrease in pressure (when you open the bottle or can) and a change in temperature (the warmer the soda, the faster the gas escapes).
* No new substances are formed. The carbon dioxide was already dissolved in the soda; it just changes from a dissolved state to a gaseous state.
In summary: While the bubbles forming in soda might make it feel like something is happening "energetically," the process is simply a physical change of carbon dioxide going from dissolved to gaseous form, and not a chemical reaction that releases heat.
