Is bread rising when yeast is added a physical or chemical change?

* Yeast consumes sugar: The yeast in bread dough consumes sugars, producing carbon dioxide gas and alcohol as byproducts.

* Gas expansion: The carbon dioxide gas gets trapped within the dough's structure, causing it to expand and rise.

* New substances formed: The original ingredients (flour, water, yeast, etc.) are transformed into new substances (bread with a different texture and taste).

Key points:

* Physical changes alter the form or appearance of a substance but don't create new substances. (e.g., melting ice)

* Chemical changes involve the formation of new substances with different chemical compositions. (e.g., burning wood)

Since the yeast's activity creates new substances (carbon dioxide and alcohol), it's a chemical change.