Physical vs. Chemical Changes Quiz

Physical Changes

• Affects physical properties of a substance without altering its chemical composition.
• Typically reversible, meaning the original state can be restored.
• No new substances are formed during the change.
• Observable changes can include state (solid, liquid, gas), size, shape, or color.
• Example: Melting of ice transforms solid to liquid while maintaining its chemical identity as H₂O.
• Example: Dissolving salt in water results in a solution where sodium chloride (NaCl) remains unchanged.
• Example: Chopping wood alters its physical form, but it remains wood.

Chemical Changes

• Involves transformation of substances into new substances with differing chemical properties.
• Usually irreversible, meaning the original substances cannot be restored.
• New substances are formed as a result of the change.
• Often accompanied by energy changes such as heat, light, or sound.
• Example: Combustion of wood produces new substances like ash, carbon dioxide (CO₂), and water (H₂O).
• Example: Rusting of iron involves a reaction with oxygen, resulting in iron oxide (rust).
• Example: Baking a cake represents a chemical reaction where ingredients transform to create new substances.

Key Differences

• Chemical Composition:

  • Physical Change: No change in the chemical structure of the substance.
  • Chemical Change: Results in the formation of new substances with altered chemical compositions.

• Reversibility:

  • Physical Change: Often reversible processes, like freezing and melting water.
  • Chemical Change: Typically irreversible under standard conditions, exemplified by baking a cake.