Question

Stirring dry yeast into a bowl of hydrogen peroxide

causes bubbles to form. Blowing air into a glass of milk
with a straw also causes bubbles to form. One of these is
a physical change, and the other is a chemical change.

Answer 1

Answer: If the reaction is a chemical change, new substances with different properties and identities are formed. This may be indicated by the production of an odor, a change in color or energy, or the formation of a solid.

Answer 2

PHYSICAL CHANGE: Blowing air into a glass of milk with a straw
This is physical because someone is causing the change

CHEMICAL CHANGE: stirring dry yeast into a bowl of hydrogen peroxide
This is a chemical change because chemicals are changing the subject. So it’s being chemically changed!