Question

unit review - matter and change
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which of these changes is an example of a physical change?
paper turns black and creates smoke when heated with a flame
an indicator changes color when it is added to an acid
dry ice changes from solid into a gas when heated
sodium creates an explosion when added to water

Explanation:

A physical change is a change in matter that does not produce a new substance, only altering its state or appearance.

• Burning paper creates new carbon-based substances (chemical change).
• An indicator changing color in acid involves a chemical reaction (chemical change).
• Dry ice (solid CO₂) subliming to gas is a state change with no new substance formed (physical change).
• Sodium reacting with water produces new substances like sodium hydroxide and hydrogen (chemical change).

Answer:

dry ice changes from solid into a gas when heated