Question

1. when a substance melts or boils, is it a physical or chemical change? explain your choice.
2. use what you have learned about chemical and physical changes to identify the type of change that occurs in each of the following. circle the correct answer.

a. digestion of food within the digestive system: physical or chemical change?
b. the yellowing of the pages of an old book: physical or chemical change?
c. the evaporation of perfume from an open bottle: physical or chemical change?
d. the cutting of a piece of paper: physical or chemical change?
e. silver tarnishing: physical or chemical change?
f. instant ice tea mix dissolving in water: physical or chemical change?
g. condensing air (turning air from a gas to a liquid): physical or chemical change?

1. which type of change can be more easily reversed: chemical or physical? please explain in detail with an example of each.

Explanation:

Step1: Define physical and chemical changes

Physical change: No new substances are formed, only the state or appearance changes. Chemical change: New substances are formed with different chemical properties.

Step2: Answer question 3

Melting or boiling a substance only changes its state (solid - liquid, liquid - gas). No new substances are formed. So it is a physical change.

Step3: Answer 4a

Digestion of food involves breaking down complex molecules into simpler ones through chemical reactions. New substances are formed. So it is a chemical change.

Step4: Answer 4b

The yellowing of old - book pages is due to chemical reactions like oxidation of paper components. New substances are formed. So it is a chemical change.

Step5: Answer 4c

The evaporation of perfume from an open bottle is a change of state from liquid to gas. No new substances are formed. So it is a physical change.

Step6: Answer 4d

Cutting a piece of paper only changes its shape and size. No new substances are formed. So it is a physical change.

Step7: Answer 4e

Silver tarnishing is a chemical reaction between silver and sulfur - containing substances in the air to form silver sulfide. New substances are formed. So it is a chemical change.

Step8: Answer 4f

Instant ice - tea mix dissolving in water is a physical process of solvation. No new substances are formed. So it is a physical change.

Step9: Answer 4g

Condensing air (gas to liquid) is a change of state. No new substances are formed. So it is a physical change.

Step10: Answer 5

Physical changes are generally more easily reversed. For example, melting ice (physical change) can be reversed by freezing the water again. Chemical changes are usually more difficult to reverse. For example, burning wood (chemical change) forms ash and other substances, and it is very difficult to turn the ash back into wood.

Answer:

1. Physical change

4a. Chemical change
4b. Chemical change
4c. Physical change
4d. Physical change
4e. Chemical change
4f. Physical change
4g. Physical change

1. Physical changes are more easily reversed. Example of physical change: Melting ice can be reversed by freezing. Example of chemical change: Burning wood is difficult to reverse as ash cannot be easily turned back into wood.