Diatomic Gases and Halogens
H, O, N, F, Cl occur as diatomic gases
Covalent bond, attain shared octet
H2 (g)
O2 (g)
N2 (g)
F2(g), Cl2 (g)
Remaining halogens also diatomic
Br2(l), I2(s)
Chapter 9 – Chemical Reactions
9.1 Reactions and Equations
9.2 Classifying Chemical Reactions
9.3 Reactions in Aqueous Solutions
Section 9.1 Reactions and Equations
Chemical reactions are represented by
balanced chemical equations.
• Recognize evidence of chemical change.
• Represent chemical reactions with equations.
• Balance chemical equations.
• Know which elements occur as diatomic molecules
and the states of these elements at room temperature;
correctly represent these elements when writing
chemical equations which involve them. [not in
chapter]
Section 9.1 Reactions and Equations
Key Concepts
• Some physical changes are evidence that indicate
a chemical reaction has occurred.
• Word equations and skeleton equations provide
important information about a chemical reaction.
• A chemical equation gives the identities and
relative amounts of the reactants and products that
are involved in a chemical reaction.
• Balancing an equation involves adjusting the
coefficients until the number of atoms of each
element is equal on both sides of the equation.
Chemical Reactions
Process by which atoms of one or more
substances are rearranged to form
different substances
Chemical Equations
Reactants are starting substances
Products are substances formed
reactant 1 + reactant 2  product 1 + product 2
+ separates 2 or more reactants or
products
 separates reactants from products
Read as “reacts to produce” or “yields”
Parts of Balanced Equation
Subscript - Shows how many atoms of an
element are present in a formula unit or
molecule of this substance
Coefficient – Shows how many formula
units or molecules are needed to balance
the equation
Chemical Equations
2 Li(s) + 2 H2O(l)  2 LiOH(aq) + H2(g)
(s) identifies solid state
(l) identifies liquid state
(g) identifies gaseous state
(aq) identifies solution in water =
aqueous solution
• LiOH(l) not the same as LiOH(aq)
Evidence of Chemical Reactions
Temperature change
Color change
Flame, smoke
Odor
Gas evolution (bubbles)
Appearance of new phase
(precipitate)
Word and Skeleton Equations
Word equation
Iron(s) + chlorine(g)  iron(III) chloride(s)
“Solid iron and chlorine gas react to
produce solid iron(III) chloride”
Skeleton equation
• Chemical formulas in place of words
Fe(s) + Cl2(g)  FeCl3(s)
Word and Skeleton Equations
Skeleton equation
Solid carbon reacts with solid sulfur to
form liquid carbon disulfide
C(s) + S(s)  CS2(l)
Note: CS2 is not an ionic compound
and ionic compound naming rules do
not apply
Practice
Write skeleton equations
Problems 1-3, page 284
Problems 67-72, p 312
Problems 1-2, page 980
Equations and Atoms
Fe(s) + Cl2(g)  FeCl3(s)
+
One iron atom
Two chlorine atoms

One iron atom
Three chlorine atoms
As written, 1 chlorine atom has been
“created” – matter not conserved
Balanced Chemical Equations
2Fe(s) + 3Cl2(g)  2FeCl3(s)
+

Both sides have:
Two iron atoms Six chlorine atoms
Balanced Chemical Equations
2Fe(s) + 3Cl2(g)  2FeCl3(s)
Skeleton equation has been balanced
by inserting correct coefficients in front
of reactants and/or products
Integers, not written if = 1
Lowest whole number ratio of amounts
of reactants and products
Balancing Chemical Equations
Steps (see table 9.2, p 286)
1 – Write skeleton equation
H2(g) + Cl2(g)  HCl(g)

+
Two H
atoms
Two Cl
atoms
One H atom
One Cl atom
Balancing Chemical Equations
2 – Count the atoms of elements in the
reactants
H2(g) + Cl2(g)  HCl(g)
2 atoms H
2 atoms Cl
Balancing Chemical Equations
3 – Count the atoms of elements in the
products
H2(g) + Cl2(g)  HCl(g)
1 atoms H
1 atoms Cl
Balancing Chemical Equations
4 – Change coefficients to make # of
atoms of each elements equal on both
sides of the equation
H2(g) + Cl2(g)  2HCl(g)
2 atoms H (both sides)
2 atoms Cl (both sides)
Balancing Chemical Equations
5 – Write the coefficients in their lowest
possible whole number ratio
H2(g) + Cl2(g)  2HCl(g)
Coefficients as written already in lowest
possible ratio
Balancing Chemical Equations
6 – Check your work.
Chemical formulas correctly written?
Number of atoms same on both sides
of equation?
All states specified?
Balancing Chemical Equations
Figure 9.6, p 288
Balancing Chemical Equations
When balanced, matter conserved
H2(g) + Cl2(g)  2HCl(g)

+
Two H
atoms
Two Cl
atoms
Two H atoms
Two Cl atoms
Balancing Equation Strategy
Balance elements that occur in only
one compound on each side first
Balance free elements last
Balance unchanged polyatomic ions as
groups (NO-3, etc)
Fractional coefficients are acceptable
as intermediate result; clear at end by
multiplication by common divisor
Balancing Chemical Equations
Combustion of propane
C3H8(g) + O2(g)  CO2(g) + H2O(g)
Count atoms on each side
C
H
O
C
H
O
3
8
2
1
2
3
Not balanced; try to balance C
Balancing Chemical Equations
C3H8(g) + O2(g)  3CO2(g) + H2O(g)
C
H
O
C
H
O
3
8
2
3
2
7
Not balanced; try to balance H
C3H8(g) + O2(g)  3CO2(g) + 4H2O(g)
C
H
O
C
H
O
3
8
2
3
8
10
Balancing Chemical Equations
C3H8(g) + O2(g)  3CO2(g) + 4H2O(g)
C
H
O
C
H
O
3
8
2
3
8
10
Not balanced; balance oxygen
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)
C
H
O
C
H
O
3
8
10
3
8
10
Done
Balancing Practice
NH3(g) + O2(g)  N2(g) + H2O(l)
?
Balance N: 2 1  1 1
Balance H: 2 1  1 3
Balance O: 2 3/2  1 3
Integers:
4326
4NH3(g) + 3O2(g)  2N2(g) + 6H2O(l)
Balancing Practice
C4H10(g) + O2(g)  CO2(g) + H2O(g)
Balance C: 1 1  4 1
Balance H: 1 1  4 5
Balance O: 1 13/2  4 5
Integers:
2 13  8 10
2C4H10(g) + 13O2(g) 
8CO2(g) + 10H2O(g)
Practice
Note: instruction to “write chemical
equation” is understood to mean “write
a balanced chemical equation”
Problems 4-6 page 287
Problems 3-8, page 980
Problems 13 page 283
Problems 64, 66, 73-75 page 312
Chapter 9 – Chemical Reactions
9.1 Reactions and Equations
9.2 Classifying Chemical Reactions
9.3 Reactions in Aqueous Solutions
Section 9.2 Classifying Chemical Reactions
There are 5 classes of chemical
reactions: synthesis, combustion,
decomposition, single replacement, and
double replacement. The replacement
reactions have subclassifications.
• Classify chemical reactions into one or more of 5
possible classes.
• Identify the characteristics of different classes of
chemical reactions, including any subclassifications
that may apply (redox, formation of hydrogen in acid,
etc.).
Section 9.2 Classifying Chemical Reactions
(cont.)
• Use the activity series for metals and for halogens to
correctly predict if a given pair of reactants will
undergo a single replacement reaction.
• Know that the products of the complete combustion of
any hydrocarbon or carbohydrate are carbon dioxide
and water.
Section 9.2 Classifying Chemical
Reactions
Key Concepts
• Classifying chemical reactions makes them easier
to understand, remember, and recognize.
• Activity series of metals and halogens can be used
to predict if single-replacement reactions will occur.
Five Classes of Reactions
Synthesis
Combustion
Decomposition
Single Replacement (4 types)
Double Replacement (3 types)
Synthesis Reactions
Two or more substances react to form
a single product A + B  C
2Na(s) + Cl2(g)  2 NaCl
CaO(s) + H2O(l)  Ca(OH)2(s)
2SO2(g) +O2(g)  2SO3(g)
Combustion Reaction
Oxygen combines with substance
A + O2(g)  C
or C + D
Energy released rapidly in form of heat
& light
2H2(g) + O2(g)  2H2O(g)
(Also a synthesis reaction)
Other reactions involve combination
with O2(g) but slow process (rusting)
Combustion
C(s) + O2(g)  CO2(g)
CH4(g) + 2 O2(g)  CO2(g) + 2H2O(g)
Combustion – Special Cases
Complete combustion of any hydrocarbon
yields CO2 & H2O as products
CH4(g) + 2 O2(g)  CO2(g) + 2H2O(g)
2C4H10(g) + 13O2(g)  8CO2(g) + 10H2O(g)
Same holds true for complete combustion of
a carbohydrate (contains CHO only)
C2H7OH = CH3CH2OH ethyl alcohol (ethanol)
4C2H7OH(l) + 13O2(g)  8CO2(g) + 14H2O(g)
Practice
Synthesis & Combustion
Problems 14-17, page 291 *
Problems 84-86 page 313
* Problem 17 has alternate accounting
system for aqueous system
Decomposition Reactions
Single compound breaks down into two
or more elements or new compounds
AB  A + B
Often require source of energy to start
• Heat, light, electricity
Decomposition Reactions
NH4NO3(s)  N2O(g) + 2H2O(g)
2NaN3(s)  2Na(s) + 3N2(g)
Practice
Problems 18-20 page 292
Problems 11-12 page 980
Problem 87, page 313
Replacement Reactions
Single-Replacement (SR)
Atoms of one element replace atoms of
another element
A + BC  AC + B
A has replaced B in compound BC
SR reactions are also redox (oxidation
reduction) reactions – will examine in
more detail in section 19.1
Single-Replacement Reactions
Categories (will discuss each in detail)
Metal replaces H atom in H2O
Metal replaces H atom in HX(aq)
One metal (solid) replaces 2d metal in
an aqueous ionic compound
Replacement of nonmetal in compound
by another nonmetal (halogens)
Single-Replacement Reactions
Metal replaces H atom in H2O
Think of H2O as HOH
2Li(s) + 2H2O(l)  2LiOH(aq) + H2(g)
Li has replaced H in HOH
Reaction occurs readily for active
metals – Li, Na, K, Rb, Ca, etc.
Elemental metal becomes a cation
Single-Replacement Reactions
Metal replaces H atom in HX(aq)
Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)
Zn has replaced H in HCl
Reaction occurs readily for more metals
than for reaction with water alone
• Depends upon T and acid strength
Elemental metal becomes a cation
Single-Replacement Reactions
One metal (solid) replaces 2d metal in
an aqueous ionic compound
M1(s) + M2X(aq)  M2(s) + M1X(aq)
M1 = metal # 1 – solid elemental
metal
M2 = metal # 2 – in ionic compound
Replacement only happens when M1
is more active (more reactive) than M2
Single-Replacement Reactions
M1(s) + M2X(aq)  M2(s) + M1X(aq)
M1 = metal # 1 – solid elemental
metal
M2 = metal # 2 – in ionic compound
M1 transformed from elemental metal
to being a cation in an ionic compound
M2 transformed from cation in an ionic
compound to being an elemental
metal
Single-Replacement Reactions
One metal (as solid) replaces another
metal in a compound dissolved in water
Cu(s) + 2AgNO3(aq) 
2Ag(s) + Cu(NO3)2(aq)
Cu has replaced Ag in AgNO3
Cu more active than Ag (see following)
Cu(s)  Cu+2 Ag+  Ag(s)
Note: Product could be CuNO3(aq)
Activity Series for Metals
Most
Active
Lithium
Rubidnium
Potassium
Calcium
Sodium
Magnesium
Aluminum
Least
Manganese
Active
Zinc
Iron
Nickel
Tin
Lead
Copper
Silver
Platinum
Gold
Single-Replacement Reactions
One metal (as solid) replaces another
metal in a compound dissolved in water
Ni(s) + NaNO3(aq)  NR
NR = no reaction
Nickel is less active than sodium (see
following slide)
Activity Series for Metals
Most
Active
Lithium
Rubidnium
Potassium
Calcium
Sodium
Magnesium
Aluminum
Least
Manganese
Active
Zinc
Iron
Nickel
Tin
Lead
Copper
Silver
Platinum
Gold
Practice – from Problem 9.2
Predict products and balance equation
Fe(s) + CuSO4(aq)  ???
Is Fe more active than Cu?
Yes
Fe(s) + CuSO4(aq)  FeSO4(aq) + Cu(s)
Balanced?
Yes
Fe(s)  Fe+2 Cu2+  Cu(s)
Practice – from Problem 9.2
Predict products and balance equation
Mg(s) + AlCl3(aq)  ???
Is Mg more active than Al?
Yes
Mg(s) + AlCl3(aq)  Al(s) +MgCl2(aq)
Balanced?
No
3Mg(s) + 2AlCl3(aq)  2Al(s) + 3MgCl2(aq)
Mg(s)  Mg+2 Al3+  Al(s)
Single-Replacement Reactions
Replacement of nonmetal in compound by
another nonmetal (halogens)
Most common for halogens
X21 + 2AX2  X22 + 2AX1
X1 = halogen number 1 X2 = halogen number 2
Replacement only happens when X1 is
more active (more reactive) than X2
X1 elemental halogen becomes anion
X2 anion halogen becomes an element
Single-Replacement Reactions
Replacement of one halogen by
another halogen
F2(g) + 2NaBr(aq)  2NaF(aq) + Br2(aq)
F has replaced Br in NaBr
Fluorine is more active than bromine
(see following slide)
Elemental fluorine has become fluoride
Bromide has become elemental bromine
Activity Series for Halogens
Most
Active
Least
Active
Fluorine
Chlorine
Bromine
Iodine
Single-Replacement Reactions
Replacement of one halogen by
another halogen
Br2(l) + MgCl2(aq)  ???
Is bromine more active than chlorine?
No
Br2(l) + MgCl2(aq)  NR
Activity Series for Halogens
Most
Active
Least
Active
Fluorine
Chlorine
Bromine
Iodine
Practice
Problems 21-24, page 295
Problem 88, page 313
Problems 13-15, pages 980-81
Single-Replacement Reactions
Summary
Active metal replaces H atom in H2O
Metal replaces H atom in HX(aq)
One metal (solid) replaces 2d metal in
an aqueous ionic compound
Replacement of nonmetal in compound
by an elemental nonmetal (halogens)
Double-Replacement Reactions
Exchange of ions between two compounds
in aqueous solution
In example shown above, hydroxide ion and
chloride ion have exchanged
Double-Replacement Reactions
One of the products is always:
• A gas
• Water
• Precipitate – solid that comes out of solution
Unlike single replacement reactions, no
elemental forms produced – elements start
as part of compound and also end that way
Double-Replacement Reactions
KCN(aq) + HBr(aq)  KBr(aq) + HCN(g)
Gaseous Product
Ca(OH)2(aq) + 2HCl(aq)  CaCl2(aq) +
2H2O(l)
Water is product
2NaOH(aq) + CuCl2(aq)  2NaCl(aq) +
Cu(OH)2(s)
Precipitate is product
Double-Replacement Reactions
Steps to determine balanced equation
See table 9.3, p 297
Step 1 – Write reactants in skeleton
Al(NO3)3(aq)
+
Na2CO3(aq)
Step 2 – Identify anions and cations
Al+3 NO3Na+ CO32Step 3 – Swap cations
Na+ NO3Al+3 CO32-
Double-Replacement Reactions
Step 4 – Write formulas for products
Al2(CO3)3(s) NaNO3(aq)
Step 5 – Write complete equation
Al(NO3)3(aq) + Na2 CO3(aq) 
Al2(CO3)3(s) + NaNO3(aq)
Step 6 – Balance equation
2Al(NO3)3(aq) + 3Na2 CO3(aq) 
Al2(CO3)3(s) + 6NaNO3(aq)
Practice
Problems 25-28, page 297
Predicting Products of Chemical Reactions
Table 9.4, p 298
Chapter 9 – Chemical Reactions
9.1 Reactions and Equations
9.2 Classifying Chemical Reactions
9.3 Reactions in Aqueous Solutions
Section 9.3 Reactions in Aqueous Solutions
Double-replacement reactions occur
between substances in aqueous
solutions and produce precipitates,
water, or gases.
• Describe aqueous solutions.
• Write complete ionic and net ionic equations for
chemical reactions in aqueous solutions.
• Predict whether reactions in aqueous solutions will
produce a precipitate, water, or a gas.
Section 9.3 Reactions in Aqueous Solutions
(cont.)
• Know the solubility rules for common cations and
anions and use them to predict the occurrence of and
formula for a precipitate.
Section 9.3 Reactions in Aqueous
Solutions
Key Concepts
• In aqueous solutions, the solvent is always water.
There are many possible solutes. Many molecular
compounds form ions when they dissolve in water.
When some ionic compounds dissolve in water, their
ions separate.
• When two aqueous solutions that contain ions as
solutes are combined, the ions might react with one
another. The solvent molecules do not usually react.
• Reactions that occur in aqueous solutions are
double-replacement reactions.
Aqueous Solutions
Water is solvent
Water-soluble substance is the solute
Solutes can be:
• Molecules (covalent) that remain intact

Sugar, ethanol
• Compounds that form ions


Ionic compounds – NaCl
Covalent compounds – HCl, NH3
Aqueous Solutions - Dissociation
NaCl(s)  Na+(aq) + Cl-(aq)
NaOH(s)  Na+(aq) + OH-(aq)
Ionic compound dissociates into
solvated (hydrated) ions that can
separate from each other
All soluble ionic compounds do this
Insoluble ionic compounds do not form
ions – otherwise, they would dissolve!
Hydration Process for Ionic NaCl
Hydrated
Ions
Na Ions
Cl Ions
H2O
Molecules
Crystal Lattice
Aqueous Solutions
HCl(g)  H+(aq) + Cl-(aq)
Despite being primarily a covalent
compound, HCl in water dissociates
into individual ions that can separate
Net Ionic Equations &
Aqueous Reactions
Three types of double replacement
reaction have a net ionic equation
Reactions that produce:
• A solid (precipitate)
• Water (neutralization)
• A gas
Reactions Forming a Precipitate
Solubility Rules
For certain common reactions, must
learn to predict when a precipitate will
form in aqueous solution
Possible to do if know solubility rules –
these are not in this chapter but are
listed on page 974 (Table R-8)
Are responsible for those rules on the
following slide [need to know all for AP]
Ionic Compounds: Solubility in H2O
Compounds of alkali metal ions and
ammonium ions are soluble
• NaCl(aq), LiOH(aq), (NH4)2CO3(aq)
Nitrates and bicarbonates compounds are
soluble
• Mg(NO3)2(aq), NaHCO3(aq)
Carbonates, phosphates, hydroxides, and
oxides are insoluble, except for compounds
with alkali metals or ammonium ion
• CaCO3(s), AlPO4(s) but Na2CO3(aq)
Ionic Compounds: Solubility in H2O
Soluble: Alkali metal, ammonium, nitrate, bicarbonate
Insoluble: Carbonate, phosphate, hydroxide, oxide
(except with cations above)
Na2S
?
Soluble (alkali)
NH4OH
?
Soluble (ammonium)
Ca3(PO4)2
?
Insoluble (phosphate)
K2CO3
?
Soluble (alkali)
MgCO3
?
Insoluble (carbonate)
(NH4)3PO4
?
Soluble (ammonium)
Ba(OH)2
?
Insoluble (hydroxide)
Precipitation Reactions
2NaOH(aq) + CuCl2(aq) 
2NaCl(aq) + Cu(OH)2(s)
Solubility rules tell you NaCl must be
soluble (alkali metal) and Cu(OH)2 must be
insoluble (hydroxide, not alkali or NH4+)
However, if you forgot hydroxide rule but
were told a precipitate forms, know the
hydroxide must be the insoluble compound
because NaCl can’t be (rule for alkali metal)
Precipitation Reactions
2NaOH(aq) + CuCl2(aq) 
2NaCl(aq) + Cu(OH)2(s)
Equation does not reveal ionic states
Use complete ionic equation to do this
This does not dissociate (it is not soluble)
2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl-(aq)

2Na+(aq) + 2Cl-(aq) + Cu(OH)2(s)
Net Ionic Equations
2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl-(aq)

2Na+(aq) + 2Cl-(aq) + Cu(OH)2(s)
Sodium and chloride ions are spectator
ions (don’t participate in reaction)
Dropping them leads to net ionic equation
2OH-(aq) + Cu2+(aq)  Cu(OH)2(s)
Practice
Problems 35-39, Page 302
Problems 99, 100 page 313
Problems 18-19, page 981
Reactions That Form Water
H+ and OH- ions can combine to form
H2O (covalent)
H+(aq) + OH-(aq)  H2O(l)
These reactions also known as acidbase or neutralization reactions
No new phase formed
• Already in aqueous phase
Reactions That Form Water
HnX type compounds are acids that
dissociate into nH+(aq) ions and Xn(aq) ions
•
•
•
•
•
X=SO4
X=Cl
X=PO4
X=NO3
X=CO3
sulfuric acid
hydrochloric acid
phosphoric acid
nitric acid
carbonic acid
n=2
n=1
n=3
n=1
n=2
Reactions That Form Water
Me(OH)m type compounds are bases
that dissociate into mOH-(aq) ions
(hydroxide) and Me+m(aq) metal ions
•
•
•
•
Me=Na
Me=K
Me=Ca
Me=Mg
sodium hydroxide m=1
potassium hydroxide m=1
calcium hydroxide m=2
magnesium hydroxide m=2
Reactions That Form Water
Equation
HBr(aq) + NaOH(aq)  H2O(l) + NaBr(aq)
Complete ionic equation
H+(aq) + Br-(aq) + Na+(aq) + OH-(aq) 
H2O(l) + Na+(aq) + Br-(aq)
Spectator ions are Na+(aq), Br-(aq)
Net ionic equation
H+(aq) + OH-(aq)  H2O(l)
Practice
Problems 40-44, page 304
Problems 100-102, page 313
Problems 20-21, page 981
Reactions That Form Gases
Carbon dioxide
CO2(g)
Hydrogen cyanide
HCN(g)
Hydrogen sulfide
H2S(g)
Carbon dioxide comes from the
decomposition reaction of carbonic
acid
H2CO3(aq)  CO2(g) + H2O(l)
Reactions That Form Gases
Equation
2HI(aq) + Li2S(aq)  H2S(g) + 2LiI(aq)
Complete Ionic Equation
2H+(aq) + 2I-(aq) + 2Li+(aq) + S2-(aq) 
H2S(g) + 2Li+(aq) + 2I-(aq)
Spectator ions are Li+(aq), I-(aq)
Net ionic equation
2H+(aq) + S2-(aq)  H2S(g)
Reactions That Form CO2
Occur when acid added to either a
bicarbonate or a carbonate
Equation 1 – double replacement
HCl(aq) + NaHCO3(aq) 
H2CO3(aq) + NaCl(aq)
Equation 2 – decomposition
H2CO3(aq)  H2O(l) + CO2(g)
Can construct overall equation by
combining individual equations
Double-Replacement Followed by
Decomposition for CO2
Reactions That Form CO2
Overall equation
HCl(aq) + NaHCO3(aq) + H2CO3(aq) 
H2CO3(aq) + NaCl(aq) + H2O(l) + CO2(g)
Cancel substances appearing on both
sides of the equation
Overall equation
HCl(aq) + NaHCO3(aq) 
NaCl(aq) + H2O(l) + CO2(g)
Reactions That Form CO2
Overall equation
HCl(aq) + NaHCO3(aq) 
NaCl(aq) + H2O(l) + CO2(g)
Complete ionic equation
H+(aq) + Cl-(aq) + Na+(aq) + HCO3-(aq) 
Na+(aq) + Cl-(aq) + H2O(l) + CO2(g)
Cancel to get net ionic equation
H+(aq) + HCO3-(aq)  H2O(l) + CO2(g)
CO2 from Carbonate
Equation 1 – double replacement
2HCl(aq) + Na2CO3(aq) 
H2CO3(aq) + 2NaCl(aq)
Equation 2 – decomposition
H2CO3(aq)  H2O(l) + CO2(g)
Can construct overall equation by
combining individual equations
CO2 from Carbonate
Overall equation
2HCl(aq) + Na2CO3(aq) + H2CO3(aq) 
H2CO3(aq) + 2NaCl(aq) + H2O(l) + CO2(g)
Cancel substances appearing on both
sides of the equation
Overall equation
2HCl(aq) + Na2CO3(aq) 
2NaCl(aq) + H2O(l) + CO2(g)
CO2 from Carbonate
Overall equation
2HCl(aq) + Na2CO3(aq) 
2NaCl(aq) + H2O(l) + CO2(g)
Complete ionic equation
2H+(aq) + 2Cl-(aq) + 2Na+(aq) + CO3-(aq) 
2Na+(aq) + 2Cl-(aq) + H2O(l) + CO2(g)
Cancel to get net ionic equation
2H+(aq) + CO32-(aq)  H2O(l) + CO2(g)
Practice
Problems 45 - 49, page 306