Question

classify the following as chemical or physical changes.
match the words in the left column to the appropriate blanks in the sentences on the right.
is unchanged
several pieces of graphite from a mechanical pencil are broken into tiny pieces. this change is
a physical change
because the matter
changes its molecular
composition
the pile of graphite is ignited with a hot flame. this change is
a chemical change
because the matter
changes its appearance but
not its molecular composition
not a change

Explanation:

• First sentence: Breaking graphite into tiny pieces is a physical change. In a physical change, the matter changes its appearance (from larger pieces to tiny pieces) but not its molecular composition. Graphite is still graphite at the molecular level.
• Second sentence: Igniting graphite with a hot flame is a chemical change. When graphite (which is carbon) burns, it reacts with oxygen (in the air) to form carbon - based compounds like carbon dioxide. So, the matter changes its molecular composition.

Answer:

• First blank (left): a physical change; Second blank (right): changes its appearance but not its molecular composition
• Third blank (left): a chemical change; Fourth blank (right): changes its molecular composition