Decide whether a physical or chemical change has occurred and give evidence for your decision. The first one has been done for you to use as an example.

Question

In a fireworks show, the fireworks explode giving off heat and light.

Answer 1

In the fireworks show example, a chemical change has occurred. The evidence for this decision includes:

1. Formation of new substances: When fireworks explode, they undergo a chemical reaction that produces gases, metals, and other compounds that were not present before the reaction.

2. Heat and light production: The explosion releases heat and light energy, which are typical indicators of chemical changes, as they often involve the breaking and forming of bonds between atoms.

3. Irreversibility: Once the fireworks have exploded, the reaction cannot be reversed to return to the original materials (e.g., gunpowder, metal salts).

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Here's another example for you:

Rusting of Iron: When iron is exposed to oxygen and moisture over time, it forms rust (iron oxide).

• Type of change: Chemical change.
• Evidence:
  1. Formation of a new substance: Rust is a different compound than the original iron.
  2. Color change: The iron changes from metallic gray to reddish-brown rust, indicating a chemical transformation.
  3. Irreversibility: Once iron has rusted, it cannot be converted back to pure iron without a chemical process.