Chemical Reactions

Which of the following are examples of chemical change?

• Digestion• Melting an ice cube• Running a car• Decomposition• Dissolving sugar in water• Boiling water• Photosynthesis• Cellular Respiration• A nail rusting

Chemical Reaction (or Chemical Change)

• The process by which the atoms of one or more substances are REARRANGED to form different substances

Evidence of a Chemical Reaction

1. Temperature change

Exothermic Reaction-heat is given off

Endothermic Reaction-heat is absorbed

Endothermic Reaction Exothermic Reaction

Classify each of the following as endothermic or exothermic.

• A log burning in the fireplace.• A chemical ice pack• Baking soda is added to vinegar causing the test

tube to become cold to the touch.• A hand warmer• Drain cleaner is added to a clogged pipe causing the

pipes to become warm.• Photosynthesis• Cellular respiration• Baking a cake

Evidence of a Chemical Reaction

2. Color Change

Evidence of a Chemical Reaction

3. Production of an Odor

Evidence of a Chemical Reaction

4. Production of a gas (bubbles)

Evidence of a Chemical Reaction

5. Formation of a solid called a precipitate

Evidence of a Chemical Reaction

6. Production of other forms of energy such as light.

Chemical equation

A written expression of a chemical reaction

Reactant Product(Starting Substance) (New substance

that forms)

Symbols used in chemical equations

+ Separates 2 or more reactants

or products

Separates reactants from

products

(s) Solid state

(l) Liquid state

(g) Gaseous State

(aq) Dissolved in water

∆ Heat is added

Chemical Equations

Reaction: Solid aluminum reacts with liquid bromine to produce solid aluminum bromide.

Word Equation-the description of a reaction is written according to the following format:

Reactant 1 + Reactant 2 Product 1

Aluminum (s) + Bromine (l) Aluminum Bromide (s)

Chemical Equations

Word Equation

Aluminum (s) + Bromine (l) Aluminum Bromide (s)

Skeleton Equation-formulas/symbols are used to represent names of compounds and elements.

Al (s) + Br2(l) AlBr3 (s)

Practice writing word and skeleton equations:

• Write the equation for the reaction observed in lab.

• Write the equation for the endothermic reaction that was observed.

Chemical Equations

• A complete chemical equation is a statement that uses chemical formulas, states of matter and coefficients to represent the substances involved and how much is needed to fully react.

Balancing Chemical Equations

A chemical equation is not complete until the atoms on the reactant side equal the atoms on the product side. COEFFICIENTS (NUMBERS IN FRONT OF THE FORMULA) are used to balance equations.

___Al (s) + ___Br2(l) ___AlBr3 (s)

Why must we balance equations?

• Law of conservation of mass-during chemical equations, matter cannot be created or destroyed. Atoms are only rearranged.

• Therefore, the number and kinds of atoms making up the reactants must be the same as those making up the products.

• Mass of reactants = Mass of products

Types of Chemical Reactions

Synthesis Reactions-

Two or more substances combine to form a single product

• General Form: A + B AB

• Example

N2 (g) + 3H2(g) 2NH3 (g)

Na2O + H2O 2NaOH

Types of Chemical Reactions

Decomposition Reactions-

A single reactant breaks down into two or more elements or new compounds

• General Form: AB A + B

• Example:

NH4NO3 (s) N2O (g) + 2H2O (g)

2HgO 2Hg + O2

Types of Chemical Reactions

Single Replacement reactions-

Atoms of one element replace atoms of another element in a compound

• General Form: A + BC B + AC

• Metals replace metals and nonmetals replace nonmetals

• Example:

Cu(s) + AgNO3(aq) 2Ag(s) + Cu(NO3)2(aq)

Cu (metal) replaces Ag (metal) in the compound because it is more reactive.

Cl2 + NaBr Br2 + NaCl

Cl2 (nonmetal) replaces Br2 (nonmetal) because it is more reactive.

Types of Chemical Reactions

How do I know if an one atom can replace another?

There is a table of reactivity. It ranks metals from most reactive (at the top) to least reactive (at the bottom)

Reactivity TableMost Active Metals Li

RbKCaNaMgAlMnZnFeNiSnPbCuAg

Least Active Metals PtAu

Most Active Nonmetals

FClBrI

Least Active Nonmetals

Which of the following reactions can take place?

• I2 + NaF F2 + NaI

• Mg + HCl MgCl2 + H2

• Cu + MgSO4 CuSO4 + Mg

• K + NaOH KOH + Na

Types of Chemical Reactions

Double Replacement Reactions-

Atoms in one compound replace atoms in another compound

General Form: AB + CD AD + CB

NaOH (aq) + CuCl2(aq) 2NaCl(aq) + Cu(OH)2 (s)

Types of Chemical Reactions

Combustion Reaction-

Combustion reactions occur when oxygen combines with a substance and energy is released (exothermic)

• General Form: CxHy + O2 CO2 + H2O

• Examples:

C (s) + O2 (g) CO2(g)

CH4 + O2 CO2 + H2O

For each of the following, identify the type of reaction

• Fe + H2SO4 Fe2(SO4)3 + H2

• C2H6 + O2 H2O + CO2

• Al + O2 Al2O3

• KClO3 KCl + O2

• KNO3 + H2CO3 K2CO3 + HNO3

Specific Rules for Reactions

• Decomposition– Metallic Carbonates, when heated,

breakdown to form metallic oxides and carbon dioxide

ZnCO3 (s) ZnO (s) + CO2 (g)

Specific Rules for Reactions

• Decomposition– Many Metallic Hydroxides when heated,

decompose into metallic oxides and water

Mg(OH)2 (s) MgO(s) + H2O (g)

Specific Rules for Reactions

• Decomposition– Metallic chlorates, when heated, decompose

into metallic chlorides and oxygen gas.

KClO3 (s) KCl (s) + O2 (g)

Specific Rules for Reactions

• Single Replacement Reaction– Replacement of hydrogen in acids by metals

2Al (s) + 6HCl (aq) 2AlCl3 (aq) + 3H2 (g)

Specific Rules for Reactions

• Single Replacement– Replacement of hydrogen in water by metals

Fe (s) + 2H2O (l) Fe(OH)2 (s) + H2 (g)

Specific Rules for Reactions

• Double Replacement Reaction– Neutralization Reaction is a type of

chemical reaction that occurs between an acid and base to produce a salt and water.

Ca(OH)2 (aq) + 2HCl (aq) CaCl2(aq) + 2H2O (l)