Post on 28-Dec-2015
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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