Chapter 5Chemical Reactions

The Nature of ReactionsTypes of Reactions

Oxidation-Reduction ReactionsBalancing Chemical Equations

Rates of change

Chemical Reactions Change Substances

•Production of gas and change in color are signs of chemical reactions

•Chemical reactions rearrange atoms– Reactant is a substance that

undergoes a chemical change.– Product is a substance that is the

result of a chemical change.

Energy and Reactions• Energy must be added to break

bonds• Forming bonds releases energy• Energy is conserved in chemical

reactions– Chemical Energy is stored energy

within atoms and molecules that can be released when a substance reacts

•Reactions that release energy are exothermic.–Exothermic reactions is a reaction that transfers energy from the reactants to the surroundings usually as heat.

Energy and Reactions

•Reactions that absorb energy are endothermic.–Endothermic reactions are those which energy is transferred to the reactants usually as heat from the surroundings

Energy and Reactions

Type of ReactionsChemical reactions are classified into four general types

Combination (Synthesis)

Decomposition

Single Replacement (Displacement)

Double Replacement (Displacement)• Play

Combination (Synthesis)

Two or more elements or simple compounds combine to form (synthesize) one product

A + B AB2Mg + O2 2MgO

2Na + Cl2 2NaCl

SO3 + H2O H2SO4

Decomposition

One substance is broken down (split) into two or more simpler substances.

AB A + B

2HgO 2Hg + O2

2KClO3 2KCl + 3 O2

• Electrolysis is the decomposition of a compound by an electric current.

Checking Your Understanding 1

Classify the following reactions as 1) combination or 2) decomposition:

___A. H2 + Br2 2HBr

___B. Al2(CO3)3 Al2O3 + 3CO2

___C. 4 Al + 3C Al4C3

Classify the following reactions as 1) combination or 2) decomposition:

_1_A. H2 + Br2 2HBr

_2_B. Al2(CO3)3 Al2O3 + 3CO2

_1_C. 4 Al + 3C Al4C3

Solution CYU 1

Single Replacement

One element takes the place of an element in a reacting compound.

A + BC AB + C

Zn + 2HCl ZnCl2 + H2

Fe + CuSO4 FeSO4 + Cu

Double Replacement

Two elements in reactants take the place of each other

AB + CD AD + CB

AgNO3 + NaCl

AgCl+NaNO3

ZnS + 2HCl ZnCl2 + H2S

Classify the following reactions as 1) single replacement 2) double replacement

__A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2

__B. Na2SO4 + 2AgNO3 Ag2SO4+2NaNO3

__C. 3C + Fe2O3 2Fe + 3CO

Checking Your Understanding 2

CYU Solution 2

Classify the following reactions as 1) single replacement 2) double replacement

1_A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2

2_B. Na2SO4 + 2AgNO3 Ag2SO4+2NaNO3

1_C. 3C + Fe2O3 2Fe + 3CO

Combustion

A reaction in which a compound (often carbon) reacts with oxygen

C + O2 CO2

CH4 + 2O2 CO2 + 2H2O

C3H8 + 5O2 3CO2 + 4H2O

C6H12O6 + 6O2 6CO2 +

6H2O

Redox till 19:55 First!

Oxidation and Reduction

Reactions that involve a loss or gain of electrons

Occurs in many of the 4 types of reactions and combustion

Important in food metabolism, batteries, rusting of metals

Nye part 1

Requirements for Oxidization-Reduction

Electrons are transferred

Two processes occur

Oxidation = Loss of electrons

Zn Zn2+ + 2e- (LEO)

Reduction = Gain of electronsCu2+ + 2e- Cu (GER)

Balanced Redox Equations

Combine the oxidation and reduction reactions to make

Loss of electrons = Gain of electrons

Zn + Cu2+ + 2e- Zn2+ + 2e- + Cu

Zn + Cu2+ Zn2+ + Cu

Gain/Loss of HydrogenIn organic and biological reactions

oxidation = Loss of Hreduction = Gain of H

Nye part 2

Checking Your Understanding

3Identify the following as an 1) oxidation or a 2 reduction process:

__A. Sn Sn4+ + 4e-

__B. Fe3+ + 1e- Fe2+

__C. Cl2 + 2e- 2Cl-

CYU Solution 3

Identify the following as an 1) oxidation or a reduction process:

1_ A. Sn Sn4+ + 4e-

2_ B. Fe3+ + 1e- Fe2+

2_ C. Cl2 + 2e- 2Cl-

Checking Your Understanding 4

In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction

Ag+ + Cl- Ag + ClA. Which reactant is oxidized

1) Ag+ 2) Cl- 3) AgB. Which reactant is reduced?

1) Ag+ 2) Cl- 3) Cl

CYU Solution 4In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction

Ag+ + Cl- Ag + ClA. Which reactant is oxidized

2) Cl- Cl- Cl + e-

B. Which reactant is reduced?1) Ag+ Ag+ + e- Ag

Nye Part 3 of 3