AB
46 Unit: Matter and Energy
INFER The bust of Abraham
Lincoln is made of bronze.
Why is the nose a different
color from the rest of the
head?
Chemical properties describe how
substances form new substances.
If you wanted to keep a campfire burning, would you add a piece
of wood or a piece of iron? You would add wood, of course, because
you know that wood burns but iron does not. Is the ability to burn a
physical property of the wood? The ability to burn seems to be quite
different from physical properties such as color, density, and shape.
More important, after the wood burns, all that is left is a pile of ashes
and some new substances in the air. The wood has obviously changed
into something else. The ability to burn, therefore, must describe another
kind of property that substances have—not a physical property but a
chemical property.
Chemical Properties and Changes
describe how substances can form new sub-
stances. Combustibility, for example, describes how well an object
can burn. Wood burns well and turns into ashes and other substances.
Can you think of a chemical property for the metal iron? Especially
when left outdoors in wet weather, iron rusts. The ability to rust is a
chemical property of iron. The metal silver does not rust, but eventually
a darker substance called tarnish forms on its surface. You may have
noticed a layer of tarnish on some silver spoons or jewelry.
The chemical properties of copper cause it to become a
blue-green color when it is exposed to air. A famous example
of tarnished copper is the Statue of Liberty. The chemical
properties of bronze are different. Some bronze objects tarnish
to a dark brown color, like the bust of Abraham Lincoln in the
photograph on the left.
Chemical properties can be identified by the changes they
produce. The change of one substance into another substance
is called a A piece of wood burning, an iron
fence rusting, and a silver spoon tarnishing are all examples of
chemical changes. A chemical change affects the substances
involved in the change. During a chemical change, combina-
tions of atoms in the original substances are rearranged to
make new substances. For example, when rust forms on iron,
the iron atoms combine with oxygen atoms in the air to form
a new substance that is made of both iron and oxygen.
A chemical change is also involved when an antacid
tablet is dropped into a glass of water. As the tablet dissolves,
bubbles of gas appear. The water and the substances in the
tablet react to form new substances. One of these substances
is carbon dioxide gas, which forms the bubbles that you see.
chemical change.
Chemical properties