Question

identify the following as physical (p) or chemical (c) changes. 1. nacl (table salt) dissolves in water. 2. ag (silver) tarnishes. 3. an apple is cut. 4. heat changes h₂o to steam. 5. baking soda reacts to vinger. 6. fe (iron) rusts. 7. alcohol evaporates. 8. ice melts. 9. milk sours. 10. sugar dissolves in water. 11. wood rots. 12. pancakes cook. 13. grass grows. 14. a tire is inflated. 15. food is digested. 16. paper towel absorbs water.

Explanation:

Step1: Recall physical - change criteria

Physical changes involve changes in size, shape, or state without forming a new substance. Chemical changes result in a new substance with different chemical properties.

Step2: Analyze each situation

1. NaCl (Table Salt) dissolves in water

It is a physical change (P) as only the state of salt changes from solid to dissolved in water without forming a new substance.

2. Ag (Silver) tarnishes

It is a chemical change (C) as silver reacts with sulfur - containing compounds in the air to form silver sulfide, a new substance.

3. An apple is cut

It is a physical change (P) as only the shape of the apple changes, no new substance is formed.

4. Heat changes H₂O to steam

It is a physical change (P) as water changes from liquid to gas state without forming a new substance.

5. Baking soda reacts to vinegar

It is a chemical change (C) as carbon - dioxide gas and other new substances are formed during the reaction.

6. Fe (Iron) rusts

It is a chemical change (C) as iron reacts with oxygen and water to form iron oxide (rust), a new substance.

7. Alcohol evaporates

It is a physical change (P) as alcohol changes from liquid to gas state without forming a new substance.

8. Ice melts

It is a physical change (P) as ice changes from solid to liquid state without forming a new substance.

9. Milk sours

It is a chemical change (C) as bacteria convert lactose in milk into lactic acid, a new substance.

10. Sugar dissolves in water

It is a physical change (P) as sugar disperses in water without forming a new substance.

11. Wood rots

It is a chemical change (C) as microorganisms break down wood into new substances.

12. Pancakes cook

It is a chemical change (C) as the heat causes chemical reactions in the batter to form new substances like cooked starches and proteins.

13. Grass grows

It is a chemical change (C) as plants use photosynthesis to convert carbon - dioxide, water, and sunlight into glucose and oxygen, new substances.

14. A tire is inflated

It is a physical change (P) as only the shape and size of the tire change due to the addition of air, no new substance is formed.

15. Food is digested

It is a chemical change (C) as enzymes break down food into smaller molecules, new substances.

16. Paper towel absorbs water

It is a physical change (P) as the water is absorbed by the paper towel without forming a new substance.

Answer:

1. P
2. C
3. P
4. P
5. C
6. C
7. P
8. P
9. C
10. P
11. C
12. C
13. C
14. P
15. C
16. P