Changes in
Matter
Chapter 12
What are
chemical
changes?
Physical and Chemical Changes
• Matter is changing all the time.
– It can go through two different types of
changes: Physical and Chemical
• A material that goes through a
physical change will still be the
same type of material.
• Examples of physical changes:
– Changes in size, shape, volume, position
– Changes in phase of matter (solid, liquid, gas)
Physical and Chemical Changes
• Material that goes through a chemical
change becomes a different type of
matter.
• The changed matter has different
properties than the original material.
– Rust is iron that has undergone a
chemical change. It has different
chemical and physical properties
than iron has.
Evidence of Chemical Change
• In a chemical change, atoms are re-
arranged to form different kinds of
matter.
• Possible signs of a chemical change.
– A change in color
– The forming of a gas or solid
Chemical Changes and
Energy Changes
• Chemical changes affect the bonds between
atoms or molecules.
– Some types of chemical changes break the bonds
apart.
– Some types of chemical changes form new bonds.
• There is an exchange of energy anytime a
chemical bond forms or is broken.
– Some materials take in energy as they change.
– Some materials give off energy when they change.
Chemical Changes and
Energy Changes
• Combustion is a chemical process.
– A burning log gives off energy as it burns.
• We feel the heat energy.
• We see the light energy.
What are some kinds of
chemical reactions?
Chemical Equations
• One or more substances change when a
chemical reaction takes place.
– The new substances have different
chemical and physical properties.
• A reactant is a substance that is used in
a reaction.
• A new substance that forms in the
reaction is called the product.
Chemical Equations
• A chemical equation is a short way to write
what goes on in a chemical reaction.
– It looks similar to a math equation.
• The reactants are shown on the left.
• The products are shown on the right.
• An arrow points from the reactants to the
products. You say the word “makes” or
“yields” for the arrow.
• Aluminum + Oxygen Aluminum Oxide
Al + O2 AlO2
Chemical Equations
2 H2O 2 H2 + O2
water makes hydrogen + oxygen
(reactant) (products)
2 Mg + O2 Mg2O2
Magnesium + oxygen makes magnesium oxide
Matter is Always Conserved
• Law of Conservation of Mass: Matter is
not made or destroyed in a chemical
reaction.
• This means that the total mass of the
reactants is equal to the total mass of the
products.
Types of Chemical Reactions
• Decomposition reactions: compounds split apart
reactant---- product + product
C12H22O11 ----> 12C + 11H2O
• Combination reactions: Elements or compounds come
together
reactant + reactant -------> product
2H2 + O2 ----> 2H2O
• Replacement reactions: one or more compounds split
apart. When they split, the parts switch places.
Reactant + reactant --- product + product
Zn + H2SO4 ----> ZnSO4 + H2
•
How are chemical
properties used?
Separating Mixtures
• You can use physical methods to
separate mixtures.
• For example
A mixture of iron filings and sulphur
can be separated by using a magnet to
attract the iron.
Iron is a magnetic material but sulphur is
not.
Separating Metals
from Ores
• Ores are rocks that have metals in them.
• The metals are often mixed with other
substances.
• Chemical properties are used to release
the metals from their ores.
• Iron ore contains iron oxide.
– When you heat iron ore, you get the products
of pure iron and carbon dioxide.
Identifying Substances
• Scientists can use chemical properties to
decide what a substance is.
• Acids and bases are two common types of
substances.
– Lemon juice and vinegar contain acids.
– Some household cleaners contain bases.
Identifying Substances
• Acids and bases can be identified by their
chemical properties.
• Tests to identify substances:
– Universal indicator paper: Acids and bases react with
chemicals to make the paper change its color.
• Strong acids turn the paper red
• Strong bases turn the paper purple
• Weaker acids and bases produce other colors
– Flame test: Material is heated in an open flame and
certain colors are seen in the flame.
• Different substances burn in different colors.
Identifying Substances
How is chemical technology
used in our lives?
Chemistry and Health
• Antibiotics: In 1928, Alexander Fleming
discovered penicillin. He was growing bacteria
and discovered that bacteria near a mold died.
Scientists then learned ways to make this mold
to create antibiotics.
– Antibiotics are medicines that kill bacteria.
• Vitamins: Chemists found that certain diseases
could be stopped if people ate certain foods.
They found that chemicals in the foods, vitamins,
cured the diseases.
Chemistry and New Materials
• Many substances, such as cotton in jeans
or wool, come from nature.
• Scientist have also invented new
materials.
• Silk is a strong, soft, smooth fiber.
– It is costly and slow to make.
• An American chemist made a fiber like
silk. He called it nylon.
Chemistry and New Materials
• Nylon is a polymer.
• A polymer is a large molecule of many
identical units linked in long chains.
– A polymer may have thousands or even
millions of units in one chain.
Chemistry and New Materials
• Plastic is another type of polymer.
– There are many types of plastics.
– Many plastics are made from chemicals found
in petroleum.
• Why plastics are useful:
– Lightweight
– Last for a long time
– Resist decay
– Not costly to make
Chemistry and New Materials
• Concrete: The main ingredient of concrete
is cement, which is a human-made
material.
– To make concrete, you mix cement with
gravel, sand, and water. A chemical reaction
takes place as the cement sets.
• Scientists have learned to
make different types of concrete.
Chemistry and Transportation
• Chemistry has given us rubber, which is very
useful for transportation.
• Rubber is used to make tires and the soles of
shoes.
• Natural rubber comes from plants.
– Pros: It bends easily and is waterproof.
– Cons: In cold temperatures, it becomes stiff and
cracks. In warm temperatures, it melts and gets
gooey.
• Scientists learned how to produce human-
made rubber.
– They heated rubber and added sulfur to it. This
man-made rubber does not bend or crack in cold
weather and does not melt in warm weather.
Chemistry and Transportation
• Chemistry also helps transportation in
other ways.
• Scientists get many products from
petroleum (crude oil).
– It contains many compounds, such as
gasoline, kerosene, and motor oil.
– Scientists have learned how to turn crude oil
into all of these materials.
Important Discoveries
• 1839: Charles Goodyear discovers a process
that makes rubber stronger.
• 1859: The first oil well in the United States is
drilled.
• 1889: Karl Benz develops one of the first cars
that runs on gasoline.
• 1909: Ammonia is first made with nitrogen from
the air. It would later be used as a fertilizer.
• 1911: The word vitamin is first used.
• 1928: Alexander Fleming discovers penicillin.
• 1935: The first nylon fiber is made.
Chemicals and Safety
• Some chemicals make life safer for us.
– Scientists have learned how to use them to
kill germs in drinking water since, in the past,
many people got sick from contaminated
drinking water.
• Chemicals such as chlorine make water safer.
Chemicals and Safety
• Chemicals can be harmful if they are used in the
wrong way.
• You should always read the warning labels on
chemicals.
• Most cleaning supplies give directions for safe use.
– You might have to wear gloves to protect your skin
or goggles to protect your eyes.
– You might have to open windows to let out strong
fumes.
• Never mix cleaners. It could lead to dangerous
chemical reactions.
– Reactions could include lung damage, burns, or
explosions.