Download Chapter 4

Chapter 3 Reactions
Combustion
Decomposition
Combination
Chapter 4 Reactions
Exchange reactions (Metathesis)
• Formation of a precipitate
• Formation of a gas
• Formation of a week or non-electrolyte
Single Displacement Reactions
• Redox reactions
• Oxidation numbers
Mary J. Bojan
Page 1
Chapter 4
Balancing Equations
Law of conservation of mass: matter
cannot be lost in any chemical reaction
Mary J. Bojan
Page 2
Chapter 4
Patterns of reactivity
Know how to balance a chemical reaction
• (Complete) Combustion reactions (Chapter 3)
C3H8(g) + 5O2 (g) → 3CO2 (g) + 4H2O(g)
• Combination reactions (Chapter 3)
2Mg(s) + O2(l) → 2MgO(s)
• Decomposition reactions (Chapter 3)
PbCO3(s) →PbO(s) + CO2(g)
• Exchange reactions (Chapter 4)
Precipitation
Pb(NO3)2(aq) + 2KI(aq) → PbI(s) ↓ + 2KNO3(aq)
Neutralization
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
Gas formation
2HCl(aq) + Na2S(aq) → H2S(g) ↑ + 2NaCl(aq)
• Single displacement reactions (Chapter 4)
2Ca(s) + O2(g) → 2CaO(s)
Mary J. Bojan
Page 3
Chapter 4
Write balanced reactions for
The combustion of ethanol CH3CH2OH
The decomposition of lead carbonate PbCO3
The combination of nitrogen and hydrogen to
form ammonia (NH3)
Mary J. Bojan
Page 4
Chapter 4
Exchange reaction
(Double Displacement)
Exchange positive ions to get products
AD + XZ → AZ + XD
Example:
Reactants:
Pb(NO3)2 + KI
Pb(NO3)2 + KI → PbI2 + KNO3
Balance the reaction.
Pb(NO3)2 +
KI → PbI2 +
KNO3
Does anything happen?
Do you have to do the reaction to know?
Mary J. Bojan
Page 5
Chapter 4
Metathesis Reactions
(Double Displacement)
Given reactants: exchange positive ions
to get products
Requires a driving force (otherwise
nothing happens)
Driving Forces
1. Precipitate forms
2. Weak or nonelectrolyte forms
3. Gas forms
How do you know what is happening?
Net Ionic Equation
Mary J. Bojan
Page 6
Chapter 4
Example: Precipitation Reaction
Mix silver nitrate and sodium chloride.
What happens?
1. Molecular Equation
2. Ionic Equation
Spectator ions:
3. Net Ionic Equation
Mary J. Bojan
Page 7
Chapter 4
SOLUBILITY RULES FOR COMMON
IONIC COMPOUNDS IN WATER
1. Almost all ammonium and alkali
metal salts are soluble.
2. Most nitrates, acetates, chlorides,
bromides, and sulfates are soluble.
Exceptions: silver halides
sulfates of Ca, Ba, Pb
3. Most sulfides, carbonates, phosphates
and hydroxides are insoluble.
Exceptions: alkali salts
ammonium salts.
(See #1 above.)
See Table 4.1 of Brown, LeMay, and Bursten for a
more comprehensive listing.
Mary J. Bojan
Page 8
Chapter 4
Formation of Weak or Nonelectrolyte
(neutralization reaction)
Acid + base → salt + water
Molecular Equation
Ionic Equation
Spectator ions:
Net Ionic Equation
Mary J. Bojan
Page 9
Chapter 4
Examples:
What is the net ionic equation for the reaction
between sodium hydroxide and acetic acid?
What is the net ionic equation for the reaction
between sodium chloride and potassium iodide?
Mary J. Bojan
Page 10
Chapter 4
GAS FORMATION
• Direct production of a gas
CO2, H2S, NO2, SO2
• Production of weak acid which decomposes.
Example:
Molecular Equation
NaHCO3(aq)+HCl(aq) → H2CO3(aq)+NaCl(aq)
↓
CO2(g)+ H2O(l)
Ionic Equation
Na+(aq) + HCO3− (aq) + H+(aq) + Cl− (aq) →
H2CO3 (aq)+ Na+(aq)+Cl− (aq)
↓
Na+(aq)+Cl− (aq)+CO2(g)+ H2O(l)
Net Ionic Equation
H+(aq) + HCO3− (aq) → CO2(g)+ H2O(l)
Mary J. Bojan
Page 11
Chapter 4
Single Displacement reactions
(Oxidation-Reduction)
Zn(s) + CuSO4(aq) → ZnSO4(aq) +Cu(s)
What is oxidized?
What is reduced?
What is the oxidizing agent?
What is the reducing agent?
Ionic equation:
Net ionic equation
Rules for determining Oxidation States
Mary J. Bojan
Page 12
Chapter 4
1. Oxidation state of atom in elemental form is zero.
e.g.
Cl2
O2
P4
C(s)
S8
2. The oxidation number of a monatomic ion equals its
charge.
3. Some elements have “common” oxidation numbers
that can be used as reference in determining the
oxidation numbers of other atoms in the compound.
Alkali metals
+1
Alkaline earth metals
+2
Fluorine
–1
Cl, Br, I
almost always
–1
O
usually –2
peroxides (–1) & superoxides possible
H
usually
+1
Hydrides: metal-H compounds (–1)
4. Sum of oxidation numbers is equal to overall
charge of molecule or ion:
• For a neutral compound the sum of oxidation
numbers equals zero.
• For a polyatomic ion, the sum of the oxidation
numbers is equal to the charge on the ion.
5. Shared electrons are assigned to the more
electronegative atom of the pair:
more electronegative atom will have a negative
oxidation number.
Mary J. Bojan
Page 13
Chapter 4
ActivitySeries
Table 4.5
Will the metal element displace the atom from its
compound in a reaction?
Na(s) + H2O(l) →
Au(s) + H2O(g) →
Zn(s) + AgNO3(aq) →
Active metals
(groups IA, IIA, Al)
very reactive!
Inactive (inert metals): jewelry metals
Do not react readily
Other metals in between
Mary J. Bojan
Page 14
Chapter 4