Question

explain why each of the following examples are not physical changes (you will have three answers): 1. digestion of food 2. sour milk 3. formation of a crystal

Explanation:

1. Digestion of food: Chemical reactions break down food into nutrients. Enzymes act on food substances, changing their chemical composition. For example, proteins are broken down into amino - acids.
2. Sour milk: Bacteria ferment lactose in milk, producing lactic acid. This is a chemical change as new substances (lactic acid) are formed.
3. Formation of a crystal: A chemical process occurs where dissolved substances come out of solution and arrange in an ordered, repeating pattern. Chemical bonds are involved in the crystal - lattice formation.

Answer:

1. Digestion of food: It is a chemical change due to enzyme - catalyzed reactions altering food's chemical makeup.
2. Sour milk: It is a chemical change as bacteria cause lactose fermentation to form lactic acid.
3. Formation of a crystal: It is a chemical change involving the arrangement of substances through chemical bonding in a lattice structure.