Some Types of Chemical Reactions: An Introduction

Activity 8
Some Types of Chemical Reactions:
An Introduction
Why?
Some common types of chemical reactions are ionization, dissociation, and precipitation.
Specific reactions corresponding to these general reaction types are associated with health issues,
environmental problems, and manufacturing processes. In order to use chemical reactions or
evaluate their effects, you need to be able to identify the type of reaction and write a balanced
equation for it.
Learning Objective
• Recognize the characteristics of some different types of chemical reactions
Success Criteria
• Identify and differentiate types of chemical reactions
• Write and balance reaction equations for each type of reaction
Prerequisites
• Activity 3: Molecular Representations
• Activity 4: Alkane Nomenclature
• Activity 5: Balanced Chemical Reaction Equations
Activity 8 —Some Types of Chemical Reactions: An Introduction 47

Model:
Types of Reactions
Table 8.1
Reaction Type / Characteristic
Ionization in water
substance reacts with water to produce ions
HCl(g) + H 2 O(l)
NH 3 (aq) + H 2 O(l)
Example
H 3 O + (aq) + Cl – (aq)
NH 4 + (aq) + OH – (aq)
Dissociation in water
substance dissociates in water to produce
ions
NaCl(s)
Co(NO 3 ) 2 (s)
Na + (aq) + Cl – (aq)
Co 2+ (aq) + 2NO 3 – (aq)
Neutralization
an acid and a base react to produce water
and a salt
Precipitation in water
a solid forms from ions in aqueous solution
Substitution reaction
one chemical species displaces another
Addition reaction
a chemical species adds to a double bond
Elimination reaction
a proton is removed, an ion leaves, and a
double bond is formed
KOH(s) + HNO 3 (aq) H 2 O + KNO 3 (aq)
Ag + (aq) + Cl – (aq) AgCl(s)
CH 3 CH 2 Br + CN – CH 3 CH 2 CN + Br –
CH 2 =CH 2 + Br 2 CH 2 Br-CH 2 Br
CH 2 Br-CH 3 + OH – CH 2 =CH 2 + H 2 O + Br –
aq = aqueous, g = gas, s = solid, l = liquid
Key Questions
1. What are the characteristics of the reactions that are described in the model that you can use to
identify the reaction? (You need to remember these characteristics; writing them will help you
remember.)
a) ionization
The substance reacts with water to form ions.
b) dissociation
The substance dissociates in water to form ions.
c) neutralization
An acid and a base react to produce water and a salt.
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Foundations of Chemistry

d) precipitation
Ions in aqueous solution react to form a solid.
e) substitution
One chemical species displaces another.
f) addition
A chemical species adds to a double bond.
g) elimination
A proton is removed, an ion is eliminated, and a double bond is formed.
Exercises
1. Balance the following reactions and identify the reaction type.
Ca(NO 3 ) 2 (s)
Ca 2+ (aq) + NO 3
– (aq)
Ca(NO 3 ) 2 (s) Ca 2+ (aq) + 2 NO 3
- (aq) dissociation
H 2 PO 4 – (aq) + H 2 O(l)
HPO 4 2– (aq) + H 3 O + (aq)
Balanced
ionization
Al 3+ (aq) + OH – (aq)
Al(OH) 3 (s)
Al 3+ (aq) + 3 OH - (aq) Al(OH) 3 (s) precipitation
NaOH(s) + HCl(aq)
H 2 O(l) + NaCl(aq)
Balanced
neutralization
2. Write two ionization reactions that occur when carbonic acid H 2 CO 3 , a diprotic acid, is added
to water. Diprotic means that two protons are acidic and can react with water and ionize.
H 2 CO 3 (aq) + H 2 O(l)
HCO 3 - (aq) + H 3 O + (aq)
HCO 3 - (aq) + H 2 O(l)
CO 3 2- (aq) + H 3 O + (aq)
Activity 8 —Some Types of Chemical Reactions: An Introduction 49

3. For the reaction between calcium nitrate and sodium sulfate in aqueous solution:
a) Write the dissociation reaction equations for calcium nitrate and sodium sulfate when they
dissolve in water.
Ca(NO 3 ) 2 (s)
Ca 2+ (aq) + 2 NO 3 - (aq)
Na 2 SO 4 (s)
2 Na + (aq) + SO 4 2- (aq)
b) Using only the ions that are actually involved, write the precipitation reaction that forms
CaSO 4 (s).
Ca 2+ (aq) + SO 4 2- (aq)
CaSO 4 (s)
Information
Your answer to Exercise 3(b) is a net ionic equation. Net ionic equation means that only the ions
that react are included. The ions that do not react are omitted from the equation even though they
are present in solution. The ions that do not react are called spectator ions.
4.
Label each of the following reactions as substitution, addition, or elimination.
+ HBr
H
Br
addition
H H
Br
I
Br
I
substitution
Br
+ NaOH + H 2 O + NaBr
elimination
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Foundations of Chemistry

Problems
1.
Label each of the following reactions as substitution, addition, or elimination. Complete the
reaction equation by filling in the boxes with the missing compounds.
+
HBr
Br
addition
Cl
CN
+ KCN
+
KCl
substitution
2. Sodium methoxide (NaOCH 3 ) dissociates to produce OCH – 3 , which reacts like OH – .
2-Bromopentane
20
and sodium methoxide can react together to form three different elimination
products and one substitution product. Draw these four possible products. Two of the elimination
products are isomers.
15
luminescence intensity
SI( x)
SII( x)
SIII( x)
10
Elimination products
trans-2-pentene
Substitution product
O
5
cis-2-pentene
0
75 80 85 90 95 100 105 110 115 120 125
1-pentene
x
wavelength in nm
Activity 8 —Some Types of Chemical Reactions: An Introduction 51

3. Identify the type of reaction and write the reaction equation for each of the following situations.
a) Ammonium chloride, NH 4 Cl, dissolves in water to produce ions.
NH 4 Cl(s) NH 4 + (aq) + Cl - (aq) dissociation
b) A solid forms when sodium hydroxide, NaOH, is added to a solution of magnesium nitrate,
Mg(NO 3 ) 2 . Write the net ionic equation for this reaction.
Mg 2+ (aq) + 2OH - (aq) Mg(OH) 2 (s) precipitation
c) Sodium hydroxide, NaOH, reacts with acetic acid, CH 3 COOH. The proton attached to
oxygen is the one that is acidic.
NaOH(aq) + CH 3 COOH(aq) NaCH 3 COO (aq) + H 2 O(l) neutralization
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Foundations of Chemistry