CM 02.2 Changes in Matter

Lesson 2.2 Changes in Matter

• Define physical change and list several common

physical changes.

observation: orderly, direct information gathering
about a phenomenon

• Define chemical change and list several indications

that a chemical change has taken place.

• Apply the law of conservation of mass to chemical

reactions.

Lesson 2.2 Changes in Matter (cont.)

Matter can undergo physical and
chemical changes.

physical change

phase change

chemical change

law of conservation of mass

Physical Changes

• A change that alters a substance without

changing its composition is known as a
physical change.

Physical Changes

• A phase change is a transition of matter from

one state to another.

• Boiling, freezing, melting, and condensing all

describe phase changes in chemistry.

Chemical Changes

• A change that involves one or more

substances turning into new substances is
called a chemical change.

• Decomposing, rusting, exploding, burning, or

oxidizing are all terms that describe chemical
changes.

Conservation of Mass

• The law of conservation of mass states

that mass is neither created nor destroyed
in a chemical reaction, it is conserved.

• The mass of the reactants equals the mass of

the products.

massreactants = massproducts

1. Use the data in the table to answer the following questions.

a) How many grams of bromine reacted?
b) How many grams of compound were formed?

Practice Problems

Aluminum and Liquid Bromine Reaction

Substance

Before Reaction

After Reaction

Aluminum

10.3 g

0.0 g

Liquid Bromine

100.0g

8.2 g

Compound

0.0g

2. From a laboratory process designed to separate water into H2
and O2 gas, a student collected 10.0 grams of hydrogen and 79.4
g of oxygen.

a) How much H2O was originally involved in the process.

Practice Problems

3. A student carefully placed 15.6 g of Na in a reactor supplied with
an excess quantity of Cl2 gas. When the reaction was complete, the
student obtained 39.7 g of NaCl.
a) Calculate how many grams of Cl2 gas reacted.
b) How many grams of Na reacted?

Practice Problems

4. A 10.0-g sample of Mg reacts with O2 to form 16.6 g of MgO

(magnesium oxide). How many grams of O2 reacted?

Practice Problems

5. 106.5 g of HCl (g) react with an unknown amount of NH3 (g) to
produce 156.3 g of NH4Cl (s).

a) How many grams of NH3 (g) reacted?
b) Is the law of conservation of mass observed in the reaction?

Justify your answer.

Practice Problems

Key Concepts

• A physical change alters the physical properties of a

substance without changing its composition.

• A chemical change, also known as a chemical reaction,

involves a change in a substance’s composition.

• In a chemical reaction, reactants form products.

• The law of conservation of mass states that mass is

neither created nor destroyed during a chemical
reaction; it is conserved.

massreactants = massproducts