Juice:

* Juice does not turn into gas in the typical sense. Juice is a liquid, and while some of the water in it might evaporate and become water vapor (a gas), the juice itself doesn't transform into gas.

* Fermentation: Some fruit juices, like apple juice, can undergo fermentation. This process, caused by yeast, converts sugars in the juice into alcohol and carbon dioxide gas. This is how hard cider is made.

Soda:

* Soda is already carbonated. That means it contains dissolved carbon dioxide gas.

* Carbon dioxide gas escapes. When you open a soda can or bottle, the pressure inside decreases, and the carbon dioxide gas starts to come out of solution, creating the bubbles you see and hear.

In summary:

* Juice doesn't normally turn into gas.

* Soda is already gassified, and the gas escapes when you open the container.