Here's how it happens:

* Yeast: Bread dough typically uses yeast as a leavening agent. Yeast is a type of fungus that consumes sugar and releases carbon dioxide as a byproduct.

* Fermentation: The yeast's consumption of sugar is called fermentation. During this process, the yeast breaks down the sugar molecules into carbon dioxide and ethanol (alcohol).

* Trapped gas: The carbon dioxide gas is trapped within the dough, causing it to rise and become airy.

This process is essential for creating the texture and structure of bread. The trapped carbon dioxide creates tiny air pockets that give bread its fluffy and light texture.

So, the chemical changes involved in making bread do indeed produce a gas, which is essential for the bread's final form.