Types of Reactions

Types of Reactions• Synthesis (Combination)• Decomposition• Single Displacement• Double Displacement• Combustion• Oxidation-Reduction (Redox)

Synthesis• In a synthesis reaction, two

substances react to form one new substance.

• A + B AB• A and B can be either an element

or a compound• 2 Na + Cl2 2 NaCl• CaO + CO2 CaCO3

Decomposition• In a decomposition reaction, one

compound breaks down into two or more simple substances.

• AB A + B• 2 HgO 2 Hg + O2

• 2 KClO3 2 KCl + 3 O2

Single Displacement• In a single displacement reaction, an

uncombined element replaces another element in a compound.

• Metals replace metals and nonmetals replace nonmetals.

• The uncombined element must be more chemically reactive than the element it is replacing in order for the reaction to occur.

• A + BC B + AC

Examples of Single Displacement Reactions• Zn + CuSO4 Cu + ZnSO4

• Cl2 + 2 NaBr 2 NaCl + Br2

• Na + H2O NaOH + H2

Double Displacement • In a double displacement reaction,

the positive and negative ions “change partners” and form two new compounds.

• Three types of products may result: a weak/nonelectrolyte, a precipitate, or a gas.

• AB + CD AD + CB

Formation of a Weak/Nonelectrolyte• HCl + NaOH NaCl + H2O• The above reaction is also referred

to as a neutralization reaction.• Neutralization reactions involve

the reaction of an acid and base to produce a salt and water.

Formation of a Precipitate• AgNO3 + NaCl AgCl + NaNO3

• The AgCl is an insoluble salt and will precipitate out of the solution.

Formation of a Gas

• 2HCl + CaCO3 CaCl2 + H2CO3

• The H2CO3 decomposes to H2O and CO2.

• 2HCl + CaCO3 CaCl2 + H2O + CO2

Another example• MnS + 2HCl MnCl2 + H2S

Combustion • In a combustion reaction, a

hydrocarbon reacts with oxygen to produce carbon dioxide and water.

• CxHy + O2 CO2 + H2O

Oxidation-Reduction (Redox) Reactions• Oxidation-reduction reactions are

those that involve the transfer of one or more electrons.

• All of the previous types of reactions except double displacement are also examples of redox reactions.

Oxidation States• Oxidation states (or oxidation numbers)

are a way to keep track of electrons in redox reactions.

• Oxidation states are obtained in covalent molecules by arbitrarily assigning the electrons to particular atoms.

• Actual charges on ions are written as n+ or n- while oxidation states (not actual charges) are written as +n or -n.

Rules for Assigning Oxidation States• The oxidation state of an atom in an element

is 0.• The oxidation state of a monatomic ion is the

same as its charge.• In compounds, fluorine is always -1.• Oxygen is usually -2.• Hydrogen is +1 if combined with nonmetals.• The sum of the oxidation states in a neutral

compound must be zero.• The sum of the oxidation states in an ion must

equal the charge on the ion.

Assigning Oxidation States• Assign the oxidation states to all atoms

in the following (Note: Check answers on following slide)CO2 COSF6 Na2S2O3

NO3- HAsO2

KMnO4 XeOF4

P4O6Na2C2O4

Answers• C=+4, O=-2• S=+6, F=-1• N=+5, O=-2• K=+1, Mn=+7, O=-2• P=+3, O=-2• C=+2, O=-2• Na=+1, S=+2, O=-2• H=+1, As=+3, O=-2• Xe=+6, O=-2, F=-1• Na=+1, C=+3, O=-2

Characteristics of Oxidation-Reduction Reactions• Redox reactions are characterized by a

transfer of electrons• Oxidation is an increase in oxidation

state or a loss of electrons.• Reduction is a decrease in oxidation

state or a gain of electrons.• OIL RIG• Oxidation is loss; Reduction is gain

Characteristics of Oxidation-Reduction Reactions (continued)• The oxidizing agent is the electron

acceptor and consequently undergoes reduction.

• The reducing agent is the electron donor and consequently undergoes oxidation.

Identifying Oxidizing and Reducing Agents.• Identify the oxidizing agent, reducing

agent, the species oxidized, and the species reduced for each of the following:

a) 2AgNO3 + Cu Cu(NO3)2 + 2Agb) 4KClO3(s) KCl(s) + 3KClO4(s)c) 3AgNO3(aq) + K3PO4(aq) Ag3PO4(s) + 3KNO3(aq)