Question

1. which activity is an example of a chemical change? *

a. dissolving table salt in water
b. hammering aluminum into thin sheets
c. melting gold to make jewelry
d. burning wood to produce ashes

1. phase changes of matter (evaporation, melting) are examples of

____________________ changes.
a. physical
b. chemical
c. atmospheric
d. mass

Explanation:

• Question 20:
• A chemical change involves the formation of new substances.
• Dissolving table salt in water (A) is a physical change as salt can be recovered by evaporation.
• Hammering aluminum into thin sheets (B) is a physical change (change in shape).
• Melting gold (C) is a physical change (change in state).
• Burning wood (D) produces new substances (ashes, carbon - dioxide, etc.), so it is a chemical change.
• Question 5:
• Phase changes (like evaporation, melting) do not change the chemical composition of the substance.
• Physical changes involve changes in state or shape without forming new substances. Chemical changes form new substances.
• Atmospheric and mass are not relevant categories for phase - change classification.

Answer:

1. D. burning wood to produce ashes
2. A. physical