Final answer:
Toasting bread is a chemical change because it causes chemical reactions that create new substances with different properties than the original bread. The Maillard reaction during toasting forms new compounds, making this process irreversible.
Step-by-step explanation:
Toast is an example of a chemical change because the process of toasting bread results in the bread undergoing chemical reactions that change its chemical composition. When you heat bread in a toaster, the carbohydrates in the bread undergo a process called the Maillard reaction, which creates new compounds like melanoidins that give toast its distinctive flavor and color. The heat also causes starches to break down into simpler sugars. These changes are not reversible, creating new substances with different chemical properties than the original bread. Therefore, toasting bread is a chemical reaction and not a physical change.