1. Section 3.2: Changes in Matter
Chapter 3
Section 3.2: Changes in Matter

2. Objectives
Define physical change and list several common physical changes.
Define chemical change and list several indications that a chemical change has taken place.
Apply the law of conservation of mass to chemical reactions.

3. Physical Changes
A physical change is a change that alters a substance without changing its composition.
Cutting your hair or crumpling a sheet of paper are examples of physical changes.
Verbs describing a physical change include: TEAR, BREAK, BEND, SPLIT, CRUSH, BOIL, FREEZE, MELT.
Note: Changes in state and ability to dissolve are physical changes.

4. Chemical Changes
A chemical change is the change of one substance into a new, different substance.
A chemical change is more commonly referred to as a chemical reaction.
Examples of chemical
changes are the
fermentation of grapes,
the rusting of iron,
and the changing color
of leaves in the fall.
Verbs describing a
chemical reaction would include…?

5. A Closer Look
Iron reacts with oxygen in the air to form a new, different substance – rust. Rust is really a compound called iron oxide.
Iron & rust have different compositions and different physical & chemical properties.
In the reaction, iron and
oxygen, the starting
substances, are called
the reactants. The new
substances produced are
called the products.

6. Evidence of a Chemical Reaction
A color change – The formation of rust is an excellent example of this.
Production of a gas – Bubbles or a change in odor indicate a gas was produced.
Formation of a precipitate –
An example of the production
of a solid in a liquid is seen in
the photo to the right.
An energy change – A change
in temperature indicates that
energy was absorbed or
released.

7. Law of Conservation of Mass
Following the invention of
the analytical balance,
scientists, like Antoine
Lavoisier, observed many
chemical reactions and
always found that the
mass before and after a
reaction did not change.

8. Law of Conservation of Mass
They summarized this phenomenon in a law: mass is neither created or destroyed during a chemical reaction – it is conserved.
Massreactants = Massproducts

9. Practice Problems
10.00 g of mercury (II) oxide is heated until it is converted to liquid mercury and oxygen gas. If the mercury has a mass of 9.26 g, what is the mass of the oxygen formed?
10.3 g of Al are allowed to react with g of Br. After the reaction, no Al remains but 8.5 g of Br remains unreacted. How many grams of the compound aluminum bromide were formed?