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When the atoms in molecules
rearrange to form new kinds of
molecules, we say a chemical
reaction has taken place.
Chemical reactions often
lead to a dramatic change.
Reactions and changes
Physical change
Not all dramatic changes are caused by
chemical reactions. When ice lollies melt,
the atoms in the water molecules do not
get rearranged into new molecules –
they remain water molecules. Melting is
simply a physical change.
What chemical reaction makes silver objects slowly turn grey and dull?
Science and technology
Escaping energy
Chemical reactions can
release energy as heat
and light. A sparkler
contains chemicals that
release a lot of energy as
light to create a dazzling
shower of sparks.
Melting is not a
chemical reaction.
Chemical change
Fire is caused by a chemical
reaction. When wood burns, the
atoms in wood are rearranged
to form new kinds of molecules.
This process releases
energy as light and
heat, producing
glowing flames.
Burning is
a chemical
reaction.
