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

What happens in a chemical reaction?

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.

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 _________

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.

Balancing a Chemical Equation • Write the unbalanced equation. • Count atom of each element in the reactants and in the products. • Add coefficients to balance the atoms. • Write the balanced chemical equation.

Reactants Elements Products

H

O

Balanced: 2Na + Cl2 => 2NaCl

Reactants Products

Coefficients

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