Question

what do these two changes have in common?
sauce burning on a stove
saliva breaking down a piece of bread
select all that apply.
both conserve mass. both are only physical changes.
both are caused by cooling. both are chemical changes.

Explanation:

• Law of conservation of mass: In any chemical reaction (which these are), mass is conserved. The total mass of reactants equals the total mass of products.
• Chemical change:
• Sauce burning on a stove: Involves a reaction with oxygen (combustion), forming new substances (e.g., carbon - dioxide, water vapor, and charred residues).
• Saliva breaking down bread: Saliva contains enzymes (like amylase) that chemically react with starch in bread to form simpler sugars.

Answer:

Both conserve mass. Both are chemical changes.