Unit 10:
Chemical Equations
Chapter Objectives
• 1. To learn to write
chemical equations
• 2. To correctly interpret
chemical equations
• 3. To balance chemical
equations
Chapter Objectives
• 4. To classify chemical reactions
• 5. To predict products of chemical
reactions
• 6. To write ionic and net ionic
equations
Chemical Reactions
• In a chemical reaction, substances join
together to form new substances
• The original substances present are
called REACTANTS
• The new substances formed are called
PRODUCTS
Discussion of Chemical Reactions
• The general form of an equation is:
• Reactants  Products
• The  is read as “yields” or “reacts to
produce”
Discussion of Chemical Reactions
• A+BC
• Substance “A” and “B” react to
produce substance “C”
Additional Symbols in Chemical
Reactions
• + used to separate reactants or
products
• (s) means chemical is in solid
state
• (l) means chemical is in liquid
state
Additional Symbols
in Chemical Reactions
• (g) means chemical is in gas state
• (aq) means chemical is dissolved in
water
• *See Table 10-1 in book (page 278)
Other Symbols
•  means something is added to the
reaction
–Usually this is heat
Pt
•
means a catalyst (Pt) is
added
Skeleton Equations
• Skeleton (Formula) Equationthe rough form of an equation
• It only shows the framework
for the chemical reaction
Write Skeleton Equations
• Sodium metal reacts with Oxygen gas to
form solid Sodium Oxide
• Solid sulfur reacts with Fluorine gas to
form gaseous Sulfur Hexafluoride when
heated
• Nitrogen reacts with Hydrogen to form
Ammonia (NH3) gas. Heat is required.
Review-Write Skeleton Equations
• 1. Magnesium metal reacts with
Chlorine to form solid Magnesium
Chloride.
• 2. Aqueous Silver Nitrate reacts with
aqueous Sodium Chloride to form
solid Silver Chloride and aqueous
sodium nitrate
Law of Conservation of Mass
• The Law of Conservation of Mass
states that mass is neither created
or destroyed in a chemical reaction
• Because of this Law, it is necessary
to balance chemical equations
Balancing Chemical Equations
• In balanced chemical equations,
each side of the equation has the
same number of atoms of each
element
• Coefficients are used to balance
chemical equations
Question
• What is the difference between a
coefficient and subscript?
• Coefficients are written before the
formulas
• Subscripts are part of the formula
• Never use SUBSCRIPTS to balance an
equation!!
Rules for Balancing Equations
• 1. Determine the correct formulas for
the reactants and products
• 2. Write the formulas for the reactants
on the left side of the arrow. Write the
formulas for the products on the right
side of the arrow
Rules Continued
• 3. Count the number of atoms of each
element present on both sides of the
equation
• 4. Balance the elements one at a time by
placing coefficients in front of the formula.
• 5. Check to make sure each atom is
balanced
Additional Rules
• 6. Check to make sure that all
coefficients are in the lowest possible
ratio
• **If no coefficient is written, the
coefficient is assumed to be “1”
Examples
•
•
•
•
Balance the following
H2 (g) + O2 (g)  H2O (l)
Na (s) + Br2 (g)  NaBr (aq)
AgNO3 (aq) + Cu(s)  Cu(NO3)2 (aq) +
Ag(s)
Classwork
• Complete Worksheet
Review-balance the
following
• 1. Fe + O2  Fe2O3
• 2. Al2O3 + H2  Al + H2O
Quiz Review - Balance
• 1. FeCl3 + NaOH  Fe(OH)3 +
NaCl
• 2. CuCl2 + NaI  CuI2 + NaCl
• 3. H2O2  H2O + O2
QUIZ
•1) C6H6 + O2  CO2 + H2O
•2) Mg + O2  MgO
• 1.QUIZ
SolidREVIEW
sulfur reacts with
gaseous fluorine to produce
aqueous sulfur hexafluoride
• 2. Magnesium metal reacts with
chlorine gas to make solid
magnesium chloride
Additional Questions
• Pb(NO3)2 + 2 NaOH  Pb(OH)2 + 2
NaNO3
• How many oxygen atoms are on the
reactant side?
• How many oxygen atoms are in 2
NaNO3?
Balancing Equations Determining Formulas
• To Balance Equations, you
must remember how to
write correct chemical
formulas
Example
• Write the balanced equation for solid
aluminum reacting with oxygen gas to
form solid aluminum oxide
• **Remember that the diatomic
elements (Mr. BrINClHOF) appear
with a subscript of two when alone
Additional Examples
• 1. Carbon reacts with Chlorine to form
Carbon Tetrachloride
• 2. Magnesium metal reacts with solid
Zinc (II) Carbonate to form solid
Magnesium Carbonate and Zinc metal
• 3. Nitrogen gas reacts with Hydrogen
gas to form Ammonia (NH3) gas
Types of Reactions
• There are five general types of
reactions:
• Synthesis
• Decomposition
• Single Displacement
• Double Displacement
• Combustion
Synthesis Reactions
• Synthesis reactions are also
called combination reactions
• A synthesis reaction occurs when
two substances combine to form a
new compound
Synthesis Reaction
Continued
• The general form of a synthesis
reaction is:
•
A + X  AX
• Substance “AX” is the only
substance formed
Examples of Synthesis Reactions
• 2 Mg (s) + O2 (g)  2 MgO (s)
• Fe (s) + Cl2 (g)  FeCl2 (s)
• U (s) + 3 F2 (g)  UF6 (g)
Decomposition Reaction
• In decomposition reactions, one
substance breaks down
(decomposes) into two or more
simpler substances
Decomposition Reactions
Cont.
• General Form of Decomposition
Reaction:
•
AX  A + X
Examples of Decomposition
Reactions

• 2 HgO (s)  2 Hg (l) + O2 (g)

• Ca(OH)2  CaO (s) + H2O (g)
• H2SO4 (aq)  SO3 (g) + H2O (l)
Write Correct Balance Equations
• 1. The synthesis of KCl
• 2. The decomposition of magnesium
oxide
• 3. The decomposition of hydrogen
peroxide (H2O2) into oxygen and water
Write Correct Balance Chemical Equations for the
following reactions
• 1. The synthesis of barium fluoride
• 2. The decomposition of Mg(OH)2 into
magnesium oxide and water
• 3. The decomposition of water
Review-Write Balanced Equations
• 1. Gaseous hydrogen reacts with
gaseous chlorine to form aqueous
hydrogen chloride
• 2. Carbon monoxide gas reacts
with gaseous oxygen to form solid
carbon dioxide
Write balanced equations
• 1. The synthesis of Iron (III) oxide
• 2. The decomposition of cobalt (IV)
oxide
• 3. The decomposition of calcium
hydroxide into calcium oxide and
water
Write Balanced Equations
• 1) Na + Cl2 
• 2) HgCl2 
• 3) Fe(OH)3 
Single Replacement Reaction
• In a single replacement reaction
(also called a displacement
reaction), an element reacts with
a compound
• A + BX  AX + B
Examples of Single
Replacement Reactions
• Mg + Zn(NO3)2  Mg(NO3)2 + Zn
• Mg + 2 AgNO3  Mg(NO3)2 (aq) +
2 Ag
Rules for Single
Replacement Reactions
• Not all single replacement
reactions occur
• You can determine if a reaction
will occur by knowing the
activity series of metals (See
Handout)
Rules for Single Replacement
• The activity series tell you if one
metal can replace another metal in a
reaction
• The Activity Series is ordered
• Any metal that is above another metal
in the activity series WILL REPLACE
the less reactive metal
Activity Series
•
•
•
•
•
•
•
Li
K
Ca
Na
Mg
Al
Zn
•
•
•
•
•
•
Fe
Pb
H*
Cu
Hg
Ag
Predict if the following
reactions will occur
• 1. Fe + H2O
• 2. Mg + LiNO3
• 3. Na + AgCl
Write balanced equations for
the following reactions
•
•
•
•
1.
2.
3.
4.
Mg + O2 
FeCl3 
Fe + ZnO 
Br2 + MgI2 
Review
•
•
•
•
•
Predict the products and balance:
1) Mg + O2 
2) HCl 
3) Na + H2SO4 
4) Ag + ZnCl2 
Double Displacement Reactions
• In a double displacement reaction,
two compounds react
• The compounds swap elements with
each other
Double Displacement Cont
• Compounds contain a positive and
negative part
• In a double displacement, the positive
parts swap places with each other as
do the negative parts
Examples
• PbCl2 (s) + Li2SO4 (aq) 
PbSO4 (s) + 2 LiCl (aq)
• ZnBr2 (aq) + 2 AgNO3 (aq) 
Zn(NO3)2 (aq) + 2 AgBr (s)
Predict the Products of the following
reactions and balance
• BaCl2 (aq) + KClO3 (aq) 
• HCl (aq) + NaOH (aq) 
• RbBr (aq) + AgCl (aq) 
Combustion Reactions
• In a combustion reaction, a
Hydrocarbon (compound
containing Hydrogen and
Carbon) reacts with Oxygen (O2)
• The products are CO2 and H2O
Example
• 2 C6H6 + 15 O212 CO2 + 6 H2O
• *Combustion Reactions commonly
require large coefficients
Guided Practice
• Write the balanced equation for the
following combustion reactions:
• a. C4H8
• b. C6H12O6
• c. C7H16
Independent Practice- Predict the
products for the following reactions
•
•
•
•
•
1.
2.
3.
4.
5.
Hf + N2  (Hf takes a +4 charge)
Mg + H2SO4 
C2H6 + O2 
Pb(NO3)2 + NaI 
Fe + O2  (Fe takes a +3 charge)
Ionic Equations
• Most ionic compound dissociate (or
break apart) when dissolved in water
to form its component ions
• For example: NaCl (aq) really looks
like Na+(aq) and Cl- (aq)
Soluble Vs. Precipitate
• Soluble means that the compound breaks down
into its ions in water
• Ex) NaCl is soluble so it forms Na+ and Cl• Insoluble means that the compound doesn’t
break down in water
Precipitate Reactions
• In double replacement reactions,
often one of the product will be
insoluble
• The insoluble product is referred to
as a precipitate
Practice
•
•
•
•
•
Determine if soluble or insoluble:
A) NaCl
B) K2O
C) Fe(NO3)3
D) AgCl
E) BaS
F) Cd(OH)2
G) FeCl3
H) PbCO3
Ionic Equations Continued
• To write a Complete Ionic Equation:
• Write the aqueous substances as ions
(leave any substances in gas, liquids, &
solids alone)
• Example:
• AgNO3 (aq) + NaCl (aq)  AgCl (s) +
NaNO3 (aq)
Writing Ionic Equations
• 1. (NH4)2S (aq) + Cd(NO3)2 (aq)
 NH4NO3 (???) + CdS (???)
• 2. Zn(NO3)2 (aq) + (NH4)2S (aq)
 ZnS (???) + NH4NO3 (???)
Spectator Ions
• Spectator Ions-Ions that are not
directly involved in a reaction
• Spectator ions show up on both
sides of the equation
• Spectator Ions cancel out
NET Ionic Equations
• Net Ionic Equation-Indicate the
particles that actually take part in a
reaction
• The Net Ionic Equation does NOT
include spectator ions
• Net Ionic Equations must be balanced
according to atoms and charge
Write Net Ionic Equations
• 1. (NH4)2S (aq) + Cd(NO3)2 (aq) 
• 2. Zn(NO3)2 (aq) + (NH4)2S (aq) 