Chapter 9 Lesson 1 covers the fundamentals of chemical reactions, including key vocabulary such as reactants, products, and the law of conservation of mass. It explains the processes of how atoms rearrange to form new substances, the significance of chemical equations, and the importance of balancing these equations. The lesson highlights the signs of chemical reactions and the principles governing the conservation of mass during such transformations.

1. Chapter 9 Lesson 1: Understanding Chemical Reactions – p 300-310 – page 1
Vocabulary
• Chemical reaction (301) – a process in which atoms of one or more substances rearrange to form one
or more new substances
• Chemical equation (304) – a description of a reaction using element symbols and chemical formulas
• Reactant (305) – the starting substances in a chemical reaction
• Product (305) – the substances produced by the chemical reaction
• Law of Conservation of mass (306) – The law of conservation of mass states that the total mass of
the reactants before a chemical reaction is the same as the total mass of the products after the
chemical reaction
• Coefficient (308) – a number placed in front of an element symbol or chemical formula in an equation
Changes in Matter
Physical Changes
Chemical Changes
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• What are chemical changes called? ______________________________________________
• A chemical reaction is a process in which atoms of one or more substances rearrange to form one or
more new substances.
Signs of a Chemical Reaction
• Changes in the physical properties of color, state of matter, and odor are all signs that a
___________________ might have occurred
• A change is ____________ is another sign.
Changes in Physical Properties
Changes in Energy
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What happens in a chemical reaction?

2. Chapter 9 Lesson 1: Understanding Chemical Reactions – p 300-310 – page 2
• Atoms rearrange to form new substances
– There are 2 types of substances: ___________________ and ______________________
– Substances have a fixed ___________________________ of atoms
– A drop of water each water molecule will have one oxygen atom bonded to two hydrogen atoms
– If this arrangement changes the substance is no longer water and a __________________
substance has formed
– The new substance will have ____________________ chemical and physical properties
– This is what happens during a chemical reaction
• Bonds break and bonds form
– Atoms rearrange when chemical _____________________ between the atoms break
– Particles are moving in all substances, even in _________________
– These particles ___________________ , or run into one another.
– If particles collide with enough energy, the bonds between the atoms can_____________,
separate, rearrange, and ______________ new bonds.
Chemical Equations
• A chemical _____________________ is a description of a reaction using element symbols and
chemical formulas
• Element symbols represent _________________________
• Chemical formulas represent ________________________
Elemental Symbols
• Each element can exist as just one atom
– C = carbon
Cu = Copper
• _______________ elements exist in nature as diatomic molecules – two atoms of the same
element bonded together.
– This is shown by a _________________________.
– H2 = hydrogen
O2 = oxygen
Chemical Formulas
• A chemical formulas uses elements’ symbols and subscripts to describe the number of atoms in a
compound
• If an element does not have a subscript, the compound contains only _____ atom of that element
Writing Chemical Equations
• A chemical equation included both the substances that react and the substances that are formed
in a chemical equation.

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Chapter 9 Lesson 1: Understanding Chemical Reactions – p 300-310 – page 3
The starting substances in a chemical reaction are the
__________________________
The substances produced by the chemical reaction are
_________________________
The arrow shows the direction of the reaction
Reactants are written _____________of the arrow and
products are written to the _________
Balanced: 2Na + Cl2 => 2NaCl
Conservation of Mass
• French chemist Antoine Lavoisier found that the total mass of the reactants _____________
equaled the total mass of the products.
• This is the law of conservation of mass, which states that the
___________________________________________ before the reaction must equal the
___________________________________________ after the chemical equation.
Atoms are conserved
• Mass is conserved because __________________ are conserved
• Bonds break and new bonds form during a chemical reaction
• However, atoms are neither______________ nor _______________________
Balance the equations
• An equation is written so that the number of atoms of each element is the_______________, or
balanced, on each side of the arrow <= IMPORTANT!
• Add________________________!
• A coefficient is a number placed in ________________of an element symbol or chemical formula
in an equation.
• ______________ coefficients can be changed when balancing an equation.
• Do not change subscripts!!! Changing subscripts changes the identities of the substances that are
in the reaction.
Coefficients
Reactants
Elements Products
H
Reactants
O
Balancing a Chemical Equation
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Write the unbalanced equation.
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Count atom of each element in the reactants and in the products.
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Add coefficients to balance the atoms.
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Write the balanced chemical equation.
Products

4. Chapter 9 Lesson 1: Understanding Chemical Reactions – p 300-310 – page 4
Balance
•____ N2 + ____ H2 → ____ NH3
•____ Al + ____ HCl → ____ AlCl3 + ____ H2 (g)
Lighting a Candle
• Lab