Chapter 4: Changes in matter

What is happening to matter in these pictures?

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What is happening to matter in these pictures?

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Physical Changes• No change in the properties of the matter• Atoms and molecules of the substance do

not change• Often changes in state or form

What is happening to matter in these pictures?

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Chemical Changes• Change the properties of the matter• Bonds between atoms are rearranged,

and new molecules are formed

What is happening to matter in these pictures?

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Nuclear Transformation• Changes happen in the nucleus of the

atom• New elements are formed

Chemical changes

How do we know that a chemical change has occurred?

• Release of a gas

• Emission or absorption of heat• Emission or absorption of light

How do we know that a chemical change has occurred?

How do we know that a chemical change has occurred?

• Change in color• Formation of a precipitate

We write out chemical changes or CHEMICAL REACTIONS in equations

CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O(g)

“Methane reacts with oxygen to form carbon dioxide and water vapor.”

“1 molecule of methane reacts with every 2 molecules of oxygen to form 1 molecule of carbon dioxide and 2 molecules of water vapor.”Before the chemical reaction

Reactants: CH4 + 2 O2 After the chemical reactionProducts: CO2 + 2 H2O

Number of atoms

Number of atoms

Rules for balancing chemical equations

1. Coefficients must be whole numbers (no fractions)

2. Coefficients have to be as small as possible3. New substances must never be added and

existing substances must never be removed4. It is easier to save oxygen and hydrogen until

last5. Check the final equation

Example #1

H2 (g) + O2 (g) H2O (l)

Before the chemical reactionReactants: H2 + O2

After the chemical reactionProducts: H2O

Number of atoms

Number of atoms

Practice #1

K2O + H2O KOH

Before the chemical reactionReactants: K2O + H2O

After the chemical reactionProducts: KOH

Number of atoms

Number of atoms

Practice #2Na + H2O NaOH + H2

Before the chemical reactionReactants: Na + H2O

After the chemical reactionProducts: NaOH + H2

Number of atoms

Number of atoms

Practice #3

The following reaction is the unbalanced equation for a chemical reaction involving iron (Fe) and water (H2O):

Fe + H2O Fe2O3 + H2

In its reduced form, what is the coefficient of hydrogen gas (H2) in the balanced equation for this reaction?

Practice #4CO2 + H2O C6H12O6 + O2

Before the chemical reactionReactants: CO2 + H2O

After the chemical reactionProducts: C6H12O6 + O2

Number of atoms

Number of atoms