Question

physical and chemical changes
decide if each example is a physical or chemical change and write it on
the line.

1. folding a piece of paper
2. freezing juice into popsicles
3. burning wood
4. stretching a rubber band
5. baking cookies
6. melting an ice cube into water
7. an iron nail rusting
8. cooking an egg
9. shaping clay into a ball
10. photosynthesis in plants
11. mixing vinegar and baking soda
12. cutting a slice of bread
13. crushing a can
14. food digesting in our bodies
15. breaking a stick in half

Explanation:

• Physical change: A change in which the form or appearance of a substance changes, but its chemical composition remains the same. Examples include changes in state (e.g., freezing, melting), changes in shape (e.g., folding, stretching, crushing, cutting, breaking), and mixing without a chemical reaction.
• Chemical change: A change in which a new substance is formed. This often involves reactions such as burning, rusting, cooking (which can cause chemical reactions in food), baking (where ingredients undergo chemical changes), photosynthesis (a complex chemical process in plants), and reactions like mixing vinegar and baking soda (which produces carbon dioxide and other new substances), and digestion (where food is broken down chemically in the body).

1. Folding a piece of paper: Only the shape changes, no new substance. So, it's a physical change.
2. Freezing juice into popsicles: Change of state (liquid to solid), no new substance. Physical change.
3. Burning wood: Produces ash, smoke (new substances). Chemical change.
4. Stretching a rubber band: Shape change, no new substance. Physical change.
5. Baking cookies: Ingredients undergo chemical reactions (e.g., flour, sugar, etc. change chemically). Chemical change.
6. Melting an ice cube into water: Change of state (solid to liquid), no new substance. Physical change.
7. An iron nail rusting: Iron reacts with oxygen and moisture to form rust (a new substance - iron oxide). Chemical change.
8. Cooking an egg: Proteins in the egg undergo chemical denaturation (structure changes at a chemical level). Chemical change.
9. Shaping clay into a ball: Shape change, no new substance. Physical change.
10. Photosynthesis in plants: Carbon dioxide and water are converted into glucose and oxygen (new substances). Chemical change.
11. Mixing vinegar and baking soda: Produces carbon dioxide, water, and sodium acetate (new substances). Chemical change.
12. Cutting a slice of bread: Shape change, no new substance. Physical change.
13. Crushing a can: Shape change, no new substance. Physical change.
14. Food digesting in our bodies: Enzymes break down food chemically (e.g., proteins to amino acids). Chemical change.
15. Breaking a stick in half: Shape change, no new substance. Physical change.

Answer:

1. Physical change
2. Physical change
3. Chemical change
4. Physical change
5. Chemical change
6. Physical change
7. Chemical change
8. Chemical change
9. Physical change
10. Chemical change
11. Chemical change
12. Physical change
13. Physical change
14. Chemical change
15. Physical change