Question

Classify each of the following changes as chemical or physical; explain your answer for each

1. Carving a piece of wood.

2. Melting a popsicle.

3. Digestion of food.

4. Condensation of water vapor o precipitation. (rain)

Answer 1

General rule: a physical change alters the form or state of a substance without making new substances; a chemical change produces one or more new substances (usually accompanied by color change, gas, heat/light change, precipitate formation, or irreversibility).

1. Carving a piece of wood — Physical change.
You are changing the shape/size of the wood but not changing its chemical identity (cellulose, lignin remain). Cutting produces sawdust but not new chemical substances.

2. Melting a popsicle — Physical change.
Melting is a phase change (solid → liquid). The composition (water and dissolved sugars/ flavors) stays the same; no new substances are formed.

3. Digestion of food — Chemical change.
Enzymes and acids break large molecules (proteins, fats, carbohydrates) into different, smaller molecules (amino acids, fatty acids, sugars). New substances and energy changes are involved.

4. Condensation of water vapor to precipitation (rain) — Physical change.
Condensation is a phase change (gas → liquid). The chemical identity (H2O) stays the same, though latent heat is released during the process.