Transcript Chapter 5

Chapter 5
Chemical Quantities and Reactions
5.5
Types of Reactions
1
Type of Reactions
Chemical reactions can be classified as
• combination reactions.
• decomposition reactions.
• single replacement reactions.
• double replacement reactions.
2
Combination
In a combination reaction,
• two or more elements form one product.
• or simple compounds combine to form one product.
A
+
B
A
B
2Mg(s) + O2(g)
2MgO(s)
2Na(s) + Cl2(g)
2NaCl(s)
SO3(g) + H2O(l)
H2SO4(aq)
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Formation of MgO
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Decomposition
In a decomposition reaction,
• one substance splits into two or more simpler
substances.
2HgO(s)
2KClO3(s)
2Hg(l) + O2(g)
2KCl(s) + 3 O2(g)
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Decomposition of HgO
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Learning Check
Classify the following reactions as
1) combination or 2) decomposition.
___A. H2(g) + Br2(g)
2HBr(l)
___B. Al2(CO3)3(s)
Al2O3(s) + 3CO2(g)
___C. 4Al(s) + 3C(s)
Al4C3(s)
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Single Replacement
In a single replacement reaction,
• one element takes the place of a different element in
another reacting compound.
Zn(s) + 2HCl(aq)
ZnCl2(aq) + H2(g)
Fe(s) + CuSO4(aq)
FeSO4(aq) + Cu(s)
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Zn and HCl is a Single Replacement Reaction
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Double Replacement
In a double replacement,
• two elements in the reactants exchange places.
AgNO3(aq) + NaCl(aq)
AgCl(s) + NaNO3(aq)
ZnS(s)
ZnCl2(aq) + H2S(g)
+ 2HCl(aq)
10
Example of a Double Replacement
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11
Learning Check
Classify the following reactions as
1) single replacement or 2) double replacement.
A. 2Al(s) + 3H2SO4(aq)
Al2(SO4)3(s) + 3H2(g)
B. Na2SO4(aq) + 2AgNO3(aq)
Ag2SO4(s) + 2NaNO3(aq)
C. 3C(s) + Fe2O3(s)
2Fe(s) + 3CO(g)
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Learning Check
Identify each reaction as 1) combination, 2) decomposition,
3) single replacement, or 4) double replacement.
A. 3Ba(s) + N2(g)
Ba3N2(s)
B. 2Ag(s) + H2S(aq)
Ag2S(s) + H2(g)
C. SiO2(s) + 4HF(aq)
SiF4(s) + 2H2O(l)
D. PbCl2(aq) + K2SO4(aq)
2KCl(aq) + PbSO4(s)
E. K2CO3(s)
K2O(aq) + CO2(g)
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Learning Check
Each of the following reactions occur in the formation of
smog or acid rain. Identify the type of reaction and
balance each.
A. NO(g) + O2(g)
NO2(s)
B. N2(g)
+ O2(g)
NO(g)
C. SO2(g) + O2(g)
SO3(g)
D. NO2(g)
NO(g) + O(g)
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Chapter 5
Chemical Quantities and Reactions
5.6
Oxidation-Reduction Reactions
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15
Oxidation and Reduction
An oxidation-reduction reaction
• provides us with energy from food.
• provides electrical energy in
batteries.
• occurs when iron rusts.
4Fe(s) + 3O2(g)
2Fe2O3(s)
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Electron Loss and Gain
An oxidation-reduction reaction involves
• a transfer of electrons from one reactant to another.
• oxidation as a loss of electrons (LEO).
• reduction as a gain of electrons (GER).
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17
Oxidation and Reduction
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18
Zn and Cu2+
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Zn(s)
silver metal
Cu2+(aq) + 2eblue solution
Zn2+(aq) + 2e-
Cu(s)
orange
oxidation
reduction
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Electron Transfer from Zn to Cu2+
Oxidation: loss of electrons
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Reduction: gain of electrons
20
Learning Check
Identify each of the following as
1) oxidation or 2) reduction.
__A. Sn(s)
Sn4+(aq) + 4e−
__B.
Fe3+(aq) + 1e−
Fe2+(aq)
__C.
Cl2(g) + 2e−
2Cl-(aq)
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Writing Oxidation and Reduction Reactions
Write the separate oxidation and reduction reactions
for the following equation.
2Cs(s) + F2(g)
2CsF(s)
A cesium atom loses an electron to form cesium ion.
Cs(s)
Cs+(s) + 1e−
oxidation
Fluorine atoms gain electrons to form fluoride ions.
F2(s) + 2e2F−(s)
reduction
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Learning Check
In light-sensitive sunglasses, UV light initiates
an oxidation-reduction reaction.
uv light
Ag+ + Cl−
Ag +
Cl
A. Which reactant is oxidized?
B. Which reactant is reduced?
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Learning Check
Identify the substances that are oxidized and reduced in
each of the following reactions.
A. Mg(s) + 2H+(aq)
B. 2Al(s) + 3Br2(g)
Mg2+(aq) + H2(g)
2AlBr3(s)
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Chapter 5
Chemical Quantities and Reactions
5.7
Mole Relationships in
Chemical Equations
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25
Law of Conservation of Mass
The law of conservation of mass indicates that in an
ordinary chemical reaction,
• matter cannot be created or destroyed.
• no change in total mass occurs in a reaction.
• mass of products is equal to mass of reactants.
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Conservation of Mass
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2 moles of Ag + 1 mole of S
2 (107.9 g)
+
1(32.1 g) =
247.9 g reactants
=
=
1 mole of Ag2S
1 (247.9 g)
247.9 g product
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Reading Equations in Moles
Consider the following equation:
4 Fe(s)
+ 3 O2(g)
2 Fe2O3(s)
This equation can be read in “moles” by placing the
word “moles of” between each coefficient and formula.
4 moles of Fe + 3 moles of O2
2 moles of Fe2O3
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Writing Mole-Mole Factors
A mole-mole factor is a ratio of the moles for any two
substances in an equation.
4Fe(s)
+ 3O2(g)
Fe and O2
Fe and Fe2O3
O2 and Fe2O3
2Fe2O3(s)
4 moles Fe and 3 moles O2
3 moles O2
4 moles Fe
4 moles Fe and 2 moles Fe2O3
2 moles Fe2O3 4 moles Fe
3 moles O2 and 2 moles Fe2O3
2 moles Fe2O3 3 moles O2
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Learning Check
Consider the following equation:
3H2(g) + N2(g)
2NH3(g)
A. A mole-mole factor for H2 and N2 is
1) 3 moles N2
2) 1 mole N2
1 mole H2
3 moles H2
3) 1 mole N2
2 moles H2
B. A mole-mole factor for NH3 and H2 is
1) 1 mole H2
2) 2 moles NH3
3) 3 moles N2
2 moles NH3
3 moles H2
2 moles NH3
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Calculations with Mole Factors
How many moles of Fe2O3 can form from 6.0 moles of
O 2?
4Fe(s) + 3O2(g)
2Fe2O3(s)
Relationship: 3 mole O2 = 2 mole Fe2O3
Use a mole-mole factor to determine the moles of Fe2O3.
6.0 mole O2 x 2 mole Fe2O3 = 4.0 moles of Fe2O3
3 mole O2
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Learning Check
How many moles of Fe are needed for the reaction of
12.0 moles of O2?
4Fe(s)
+ 3O2(g)
2Fe2O3(s)
1) 3.00 moles of Fe
2) 9.00 moles of Fe
3) 16.0 moles of Fe
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Study Tip: Mole Factors
In a problem, identify the compounds given and needed.
How many moles of Fe are needed for the reaction of
12.0 moles of O2?
4Fe(s) + 3O2(g)
2Fe2O3(s)
The possible mole factors for the solution are
4 moles Fe
3 moles O2
and
3 moles O2
4 moles Fe
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Chapter 5
Chemical Quantities and Reactions
5.8
Mass Calculations for Reactions
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Moles to Grams
Suppose we want to determine the mass (g) of NH3
that can form from 2.50 moles of N2.
N2(g) + 3H2(g)
2NH3(g)
The plan needed would be
moles N2
moles NH3
grams NH3
The factors needed would be:
mole factor NH3/N2 and the molar mass NH3
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Moles to Grams
The setup for the solution would be:
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Learning Check
How many grams of O2 are needed to produce
0.400 mole of Fe2O3 in the following reaction?
4Fe(s)
+ 3O2(g)
2Fe2O3(s)
1) 38.4 g of O2
2) 19.2 g of O2
3) 1.90 g of O2
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Calculating the Mass of a Reactant
The reaction between H2 and O2 produces 13.1 g of water.
How many grams of O2 reacted?
2 H2(g)
+ O2(g)
2 H2O(g)
?g
13.1 g
The plan and factors would be
g H2O
mole H2O
mole O2
molar
mole-mole
mass H2O
factor
g of O2
molar
mass O2
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Calculating the Mass of a Reactant
The setup would be:
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Learning Check
Acetylene gas, C2H2, burns in the oxyacetylene torch
for welding. How many grams of C2H2 are burned if
the reaction produces 75.0 g of CO2?
2C2H2(g) + 5O2(g)
4CO2(g) + 2H2O(g)
1) 88.6 g of C2H2
2) 44.3 g of C2H2
3) 22.2 g of C2H2
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Calculating the Mass of Product
When 18.6 g of ethane gas, C2H6, burns in oxygen, how
many grams of CO2 are produced?
2C2H6(g) + 7O2(g)
18.6 g
4CO2(g) + 6H2O(g)
?g
The plan and factors would be
g C2H6
mole C2H6
molar
mass C2H6
mole CO2
mole-mole
factor
g of CO2
molar
mass CO2
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Learning Check
How many grams of H2O are produced when 35.8 g of
C3H8 react by the following equation?
C3H8(g) + 5O2(g)
3CO2(g) + 4H2O(g)
1) 14.6 g of H2O
2) 58.6 g of H2O
3) 117 g of H2O
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Chapter 5
Chemical Quantities and Reactions
5.9
Energy in Chemical Reactions
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Collision Theory of Reactions
A chemical reaction occurs when
• collisions between molecules have sufficient energy to
break the bonds in the reactants.
• bonds between atoms of the reactants (N2 and O2) are
broken and new bonds (NO) can form.
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Activation Energy
• The activation energy
is the minimum
energy needed for a
reaction to take place.
• When a collision
provides energy equal
to or greater than the
activation energy,
product can form.
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Exothermic Reactions
In an exothermic reaction,
• heat is released.
• the energy of the products is less
than the energy of the reactants.
• heat is a product.
C(s) + 2H2(g)
CH4(g) + 18 kcal
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Endothermic Reactions
In an endothermic reaction
• Heat is absorbed.
• The energy of the products
is greater than the energy of
the reactants.
• Heat is a reactant (added).
N2(g) + O2 (g) + 43.3 kcal
2NO(g)
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Learning Check
Identify each reaction as
1) exothermic or 2) endothermic.
A. N2 + 3H2
B. CaCO3 + 133 kcal
C. 2SO2 + O2
2NH3 + 22 kcal
CaO + CO2
2SO3 + heat
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Rate of Reaction
Reaction rate
• is the speed at which reactant is used up.
• is the speed at which product forms.
• increases when temperature rises because
reacting molecules move faster, providing
more colliding molecules with energy of
activation.
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Reaction Rate and Catalysts
A catalyst
• increases the rate
of a reaction.
• lowers the energy
of activation.
• is not used up
during the
reaction.
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Summary
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Learning Check
State the effect of each on the rate of reaction as:
1) increases
2) decreases 3) no change
A. increasing the temperature.
B. removing some of the reactants.
C. adding a catalyst.
D. placing the reaction flask in ice.
E. increasing the concentration of one of the reactants.
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Learning Check
Indicate the effect of each factor listed on the rate of the
following reaction as:
1) increases 2) decreases 3) none
2CO(g) + O2(g)
2CO2 (g)
A.
B.
C.
D.
raising the temperature
adding O2
adding a catalyst
lowering the temperature
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Summary of Factors That Increase Reaction Rate
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