Chapter 11
Chemical Reactions
Writing Chemical Equations
Reactants
Iron
→ Products
+ Oxygen → Iron (III)Oxide
Fe(s) + O2(g) → Fe2O3(s)
Symbols used in Equations
+
Used to separate two reactants/products
→
“Yields” separates reactants from products
↔
Used for reversible reactions
(s)
A substance in a solid state
(l)
A substance in a liquid state
(aq)
An aqueous solution, substance dissolved in
water
(g)
A substance in a gaseous state
∆ heat Heat is supplied to the reaction
→ →
Balancing Chemical Equations
 H2
+ O2 → H2O
 Each
side of the equation has the same number of
atoms of each element
 2H2
+ O2 → 2H2O
 Metals
and noble gases exist as a monoatomic molecule
 Certain
nonmetals can only exist bonded with itself in
nature: Br2, I2, N2, Cl2, H2,O2, F2 (these are diatomic
molecules)
Sample Exercise
Balance the equation.
__AgNO3 + __H2S → __ Ag2S + __ HNO3
2 AgNO3 + H2S → Ag2S + 2 HNO3
Sample Exercise
Balance the equation.
__Zn(OH)2
+ __H3PO4 → __Zn3(PO4)2 + __H2O
3 Zn(OH)2 + 2 H3PO4 → Zn3(PO4)2 + 3 H2O
Sample Exercise
Balance the equation.
__FeCl3
+ __NaOH → __Fe(OH)3 + __NaCl
FeCl3 + 3 NaOH → Fe(OH)3 + 3 NaCl
Sample Exercise
Balance the equation.
__CS2
+ __Cl2 → __CCl4 + __S2Cl2
CS2 + 3 Cl2 → CCl4 + S2Cl2
Sample Exercise
Iron
metal and chlorine gas react to form solid
iron (II) chloride
Fe (s) + Cl2 (g) → FeCl2 (s)
Sample Exercise
Iron (III) chloride + calcium hydroxide → iron (III) hydroxide +
calcium chloride
FeCl3 + Ca(OH)2 → Fe(OH)3 + CaCl2
2 FeCl3 + 3 Ca(OH)2 → 2 Fe(OH)3 + 3 CaCl2
Types of Reactions

There are 5 types of reactions
1.
Combination (synthesis) reactions
2.
Decomposition reactions
3.
Single replacement reactions
4.
Double replacement reactions
5.
Combustion reactions
1. Combination Reactions
 Two
or more substances react to form a single substance
 Also
known as synthesis reaction
 General
Equation R + S → RS
 Ex:
2S(s) + 3O2(g) → 2SO3(g)
 Ex:
Fe(s) + S(s) → FeS(s)
2. Decomposition Reactions
A
single compound is broken down into two or
more products
 General
 Ex:
Equation: RS → R + S
CaCO3 → CaO + CO2
3. Single – Replacement Reactions
 Atoms
of an element replace the atoms of a
second element in a compound
 General
 Ex:
Formula: T + RS → TS + R
Fe + CuSO4 → FeSO4 + Cu
 When
one metal displaces another metal from a
compound, it depends on the relative reactivities
of the two metals
Activity Series
 Table
 Lists
A
J
metals in order of decreasing activity
reactive metal will replace any metal listed
below it in the activity series
Sample Exercise
Write
a balanced chemical equation for the
single-replacement reaction
__Fe(s) + __ Pb(NO3)2(aq) →
Fe(s) + Pb(NO3)2(aq) → Fe(NO3)2(aq) + Pb (s)
Sample Exercise
Write a balanced chemical equation for the
single-replacement reaction
__
Cl2(g) + __ NaI(aq) →
Cl2(g) + 2 NaI(aq) → 2 NaCl + I2
Sample Exercise
Write
a balanced chemical equation for
the single-replacement reaction
__ Ca(s) + __ H2O(l) →
Ca(s) + H2O(l) → Ca(OH)2(aq) + H2(g)
4. Double – Replacement Reactions
 Involve
an exchange of positive ions between two
compounds
 General
 Ex:
Equation: RS + TU → RU + TS
Na2S(aq) + Cd(NO3)2(aq) → CdS(s) + 2Na2NO3(aq)
Sample Exercise
Write balanced chemical equations for these double –
replacement reactions
__
CaBr2(aq) + __ AgNO3(aq) →
CaBr2(aq) + 2 AgNO3(aq) → Ca(NO3)2(aq) + 2 AgBr(s)
Sample Exercise
Write balanced chemical equations for the
double – replacement reaction
__
FeS(aq) + __ HCl(aq) →
FeS(aq) + 2 HCl(aq) → FeCl2(aq) + H2S(g)
Sample Exercise
Write balanced chemical equations for the
double – replacement reaction
__
NaOH(aq) + __ Fe(NO3)3(aq) →
3 NaOH(aq) + Fe(NO3)3(aq) → 3 NaNO3(aq) + Fe(OH)3(s)
Sample Exercise
Write balanced chemical equations for the
double – replacement reaction
__
Ba(NO3)2(aq) + __ H3PO4(aq) →
3 Ba(NO3)2(aq) + 2 H3PO4(aq) → Ba3(PO4)2(s) + 6 HNO3(aq)
5. Combustion Reactions
 An
element or a compound
(usually a hydrocarbon – CnHn) reacts with oxygen
 General
 CxHy
equation:
+ O2 → CO2 + H2O
 Products
are usually carbon dioxide and water
 Ex:
CH4 + 2O2  CO2 + 2H2O
 Ex:
2Mg + O2 → 2MgO
Sample Exercise
Write
a balanced equation for the complete
combustion of these compounds:
Benzene
C6H6
Sample Exercise
Write
a balanced equation for the
complete combustion of the compound:
Methanol
CH3OH
Sample Exercise
Write
a balanced equation for the
complete combustion of the compound:
Glucose
C6H12O6