Question

Nio conducts a science experiment. He puts yeast into a bottle with water and sugar, and then caps the bottle with a balloon. He returns two hours later and notices there are bubbles on the surface of the mixture in the bottle and that the balloon has inflated, but there are no other apparent changes.

What most likely happened?

a non-chemical change, because there are no indicators of chemical changes taking place
a chemical change, because the mixture changed color
a chemical change, because a gas was produced
a non-chemical change, because the changes that occurred are reversible

Answer 1

A chemical change, because a gas was produced.

Yeast ferments the sugar in water, producing new substances (notably carbon dioxide gas and ethanol). The CO2 forms bubbles and inflates the balloon — evidence of a chemical reaction. The lack of a color change or easy reversibility doesn't mean no chemical change occurred.