Nick is researching why baking powder is a common baking ingredient. He learns that baking powder contains tartaric acid and sodium hydrogen carbonate. He also learns that when water is added to cake ingredients, a reaction occurs. It causes bubbles to form that make the cake rise. What gas is in the bubbles, and why do they form?

carbon dioxide gas

Explanation:

Leavening may be achieved by the process of fermentation, which releases carbon dioxide gas. Bakers' yeast, composed of living cells of the yeast strain Saccharomyces cerevisiae, is available as a pressed cake and in a powdered form.

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.