Chemical
Equation
Chemical Equation
• Includes the substances being reacted (reactants),
the substances being formed (products), the phases
of each of the substances, the number of moles of
each substance, and the resultant energy change.
Reactants  Products
• Coefficients are placed in front of the substance
symbols to denote a mole ratio that is in accordance
with the Law of Conservation of Mass.
HCl (aq) + Zn (s)  H2 (g) + ZnCl2 (aq)
(reactants)
(products)
• This says that hydrochloric acid reacts with zinc
metal to form hydrogen gas and zinc chloride.
Word Equations
• A WORD EQUATION describes chemical change using the
names of the reactants and products.
Write the word equation for the reaction of methane gas with
oxygen gas to form carbon dioxide and water.
methane + oxygen
Reactant
CH4 + 2 O2
carbon dioxide + water
Product
+
2 H2O
CO2
Checking for understanding
Write the word equation:
Zn + HCl  ZnCl2 + H2
Ca(OH)2 + H3PO4  Ca3(PO4)2 + H2O
6HCl + Fe2O3  2FeCl3 + 3H2O
Click Below for the Video Lectures
Symbolic Representation
Balancing
Equation
The Law of Conservation of Mass
Mass cannot be created or destroyed by physical or
chemical change.
• The elements found in the reactants can be the only
elements found in the products, and there must be equal
numbers of moles of those elements on both sides.
HCl (aq) + Zn (s)  H2 (g) + ZnCl2 (aq)
• Balancing equations involves placing coefficients that act
as multipliers in front of a substance's formula.
2 HCl (aq) + Zn (s)  H2 (g) + ZnCl2 (aq)
• This shows that 2 moles of HCl are required to react with
1 mole of Zn.
Visualizing a Chemical Reaction
2 Na
10 mole Na
___
+
Cl2
5 mole Cl2
___
2 NaCl
10
? mole NaCl
___
Visualizing a Chemical Reaction
2 Na
+
Cl2
2 NaCl
Tips for Balancing Equation
2 Cl
2 Cl means that
there are TWO
ATOMS of
chlorine.
vs
Cl2
Cl2 means that
there is one
molecule of
diatomic
chlorine.
Diatomic molecules (Br2, I2, N2, Cl2, H2, O2, F2) exist
whenever these elements are not in a compound with
another element.
Tips for Balancing Equation
• NEVER CHANGE THE CHEMICAL FORMULA!!!
• You can ONLY write coefficients to balance!
3PO4
COEFFICIENT
CHEMICAL FORMULA
Separation of NaCl
• In NaCl, there is one Cl-1 ion (since Na is
charged +1), but if that chlorine is
separated from that compound:
NaCl  Na + Cl
• Then the Cl’s thus formed will pair up
diatomically, which throws off the
balancing:
NaCl  Na + Cl2
Ex.1: carbon reacts with oxygen gas to produce carbon
dioxide:
C
O
C
1
+
O2 
2
CO2
1
2
already balanced- 1: 1: 1
Ex.2: hydrogen gas reacts with oxygen gas to produce water:
2H2 +
H 2x2=4
O
balanced ratio-
2: 1: 2
O2  2H2O
2x2 =4
2
2x1=2
Balance the following equations
• ZnS + O2  ZnO + SO2
2ZnS + 3O2  2ZnO + 2SO2
• Br2 + FeI3  I2 + FeBr3
3Br2 + 2FeI3  3I2 + 2FeBr3
<Even and Odd rule>
Start off by putting an even number
on the elements that are odd.
1.
2
3
___NaClO

___NaCl
+
___O
2
3
2
2.
4
3
4
___Fe3O4 + ___H

___Fe
+
___H
2
2O
(Fe Single element)
Sample Problems:
1. Hydrogen + oxygen  water
2 H2
+ O2
2 H2O
2. Zinc + hydrochloric acid  zinc chloride + hydrogen
Zn + 2 HCl
ZnCl2
+ H2
3. Copper + silver nitrate  cupric nitrate + silver
Cu
+ 2 AgNO3
Cu(NO3)2
+ 2Ag
(Keep NO3 together)
4. Ferric hydroxide  iron (III) oxide + water
2 Fe(OH)3
Fe2O3
+ 3 H2O
(O in multiple comp)
Click Below for the Video Lectures
Conservation of Atoms
5. Ethane (C2H6) + oxygen  carbon dioxide + water
2 C2H6
+ 7 O2
4 CO2
+
6 H2O
6. Calcium + water  calcium hydroxide + hydrogen
Ca + 2 H2O
Ca(OH)2
+
H2
7. Potassium + sulfuric acid  potassium sulfate + hydrogen
2 K
+
H2SO4
K2SO4
+ H2
8. Calcium nitrate + aluminum sulfite  calcium sulfite
+ aluminum nitrate
3 Ca(NO3)2
+ Al2(SO3)3
3 CaSO3
+ 2 Al(NO3)3
9. Phosphoric acid is formed when crystalline diphosphorus
pentoxide is dissolved in water.
P2O5
+ 3 H2O
2 H3PO4
Reaction
Types
Combustion
occur when a compound or element react with oxygen to
release energy and produce an oxide
C3H8 + 5O2  3CO2 + 4H2O
H
H
H
H
H
C CH C
H
H
+
OO
OO
OO
OO
OO
CO
O C O
O C O
O
H
+
O
H
H
O
H
H
O
H
H
O
H
+
General Form: CXHY + O2  CO2 + H2O
Real World Application COMBUSTION
• The burning of coal, a type of fossil fuel, is one of the most common
real world applications of combustion to produce heat and energy.
Combustion of coal, petroleum, hydrogen, biomass, etc. generates the
largest amount of electricity worldwide. In the U.S., energy from coal is
the major source (46.5%) of electricity production from June 2008 to
June 2009.
• As a common combustion product, CO2 is critical for global warming.
Combustion of coal emits by far the greatest amount of CO2 for the
same amount of energy comparing to other types of energy sources.
• Other sources of energy include nuclear energy, renewable energy such
as wind energy and solar energy, and so on, but they have constrains
such as safety and cost. Although it might take decades to improve
energy production technologies, they should be developed to provide
more environmentally friendly and reliable energy sources for the
future.
Synthesis Reaction
Direct combination reaction
Two elements combine to form a compound
2 Na +
Cl2

Na
Cl 
Na
Cl
2 NaCl
General form: A + B  AB
Formation of a solid: AgCl
AgNO3(aq) + KCl(aq)  KNO3 (aq) + AgCl(s)
Real World Application SYNTHESIS
• In chemical industry, the famous reaction of hydrogen
gas and chlorine gas is applied in making hydrochloric
acid.
• H2 + Cl2 → 2HCl
• The rusting of iron can also be categorized as
combination reaction. It is actually a very complicated
reaction of iron, oxygen and water forming iron rust.
• Burning of coal : C + O2 → CO2
• Discharging of a battery is usually a combination
reaction. For example, oxyhydrogen fuel cell:
• 2H2 + O2 → 2H2O
Decomposition Reaction
Reverse of synthesis
a compound decomposes into its original elements
2 H2O
H
O
O
2 H2 + O2
H
H
+
H
General form: AB  A + B
Be careful!
• DO NOT split the formula and rewrite.
• MUST check the diatomic molecule!!!
DIATOMIC
MOLECULE
!!!!!!!!!!!
2 H2O  H2 +WRONG!
O
 H2 + O2
CORRECT!
Real World Application DECOMPOSITION
• Decomposition reactions are used when heating
CaCO3 to make carbon dioxide. This practice is widely
used in today's chemical industry.
• In the chemistry industry, decomposition reactions are
applied to make high-purity hydrogen by electrolyzing
water.
• When nitroglycerin, a primary ingredient in explosives,
detonates, it rapidly decomposes to small gaseous
molecules, such as carbon dioxide and water.
Single Replacement Reaction
replace one element from a compound with
another element
ZnCl2 + Cu
CuCl2 + Zn
Cl
Cu
+
Cl
Zn

Cl
Zn
+
Cu
Cl
General form: A + BC  B + AC where A is a metal, or
A + BC  C + BA where A is a non-metal
Be careful!
• DO NOT split the formula and rewrite.
• MUST check the ion and charges!!!
Zn + HNO3 
Charges are not
+2
-1
balanced! Diatomic
ZnNO3 + H Molecule
WRONG!
Zn(NO3)2 + H2
CORRECT!
Single Replacement Reaction Practice
+3
2
+1
-2
Al + 3 Ag
Ag22CO
CO33 
1. Label the charges above each
ion
2. Check the activity series
3. Write the product by
balancing the charges
4. Balance the reaction
Al2(CO3)3 +
Ag
ABOVE CAN
REPLACE
BELOW
Predict if these reactions will occur
3 Mg + 2 AlCl3
Can magnesium replace aluminum?
2 Al + 3 MgCl2
YES, magnesium is more reactive than aluminum.
Activity Series
Al + MgCl2
Can aluminum replace magnesium?
Activity Series
MgCl2
+ Al
No reaction
NO, aluminum is less reactive than magnesium.
Therefore, no reaction will occur.
No reaction
Order of reactants
DOES NOT
determine how
they react.
The question we must ask is can the single element replace its counterpart?
metal replaces metal or nonmetal replaces nonmetal.
Real World Application
SINGLE REPLACEMENT
• In the steel industry, coke (a kind of coal) is used to
replace iron out of ferric oxide.
• Another example is the Statue of Liberty, which has
copper on the outside and iron as inner support. As
time goes by, copper starts to react with air and form a
verdigris coat; meanwhile, a single replacement reaction
between iron and verdigris takes place so that verdigris
on the outside is replaced back to copper but the iron
support is oxidized and rusted. As a result, the entire
inner support of the Statue of Liberty had to be replaced
in the 1980s.
Double Displacement Reaction
Two solutions react to form a precipitate (solid) and another
solution.
MgO + CaS  MgS + CaO
Mg
O
+
Ca
S
General Form:

Mg
S
+
Ca
O
AB + CD  AD + CB
Be careful!
• DO NOT split the formula and rewrite.
• MUST check the ion and charges!!!
K2CrO4 + 2AgNO3 
Charges
+1
-2
are not
AgCrO4 balanced!
KNO3WRONG!
+
 KNO3 + Ag2CrO4
CORRECT!
Precipitate
• Insoluble ions remain together.
• This is because the attractions
K2CrO4 + 2AgNO3
between the ions are too
 Ag2CrO4 + 2KNO3
strong for water molecules to
tear apart.
• The ions come together and
form crystals, which make the
solution cloudy.
• The crystals are pulled to the
bottom of the solution by
gravity, forming a PRECIPITATE.
Solubility Rules
• Solubility rules can used to determine if a
reaction will occur in a double displacement
reaction.
• If both the products are soluble (form ions in
solution), then no reaction has occurred.
Double Displacement Reaction
3CoCl2(aq) + 2Na3PO4(aq)  Co3(PO4)2(s) + 6NaCl(aq)
Will this reaction occur?
A reaction will occur
only if the following
will be produced
1)Gas
2)Solid precipitate
Solubility
table
Precipitate
Verifying Solubility
Use your solubility chart to verity if the
compound is soluble in water?
a)
b)
c)
d)
e)
MgCO3
AgNO3
MgCl2
Na3PO4
KOH
Insoluble
Soluble
Soluble
Soluble
Insoluble
Double Replacement Reaction Practice
+1
-3
2 Na3PO4 (aq) + 3
+2
-1
Mg(NO3)2 (aq)6 NaNO
+ Mg
Mg3(PO
(PO4))2(s)
3 (aq)
NaNO
+
3
3
4 2
INSOLUBLE
1. Label the charges above each
ion
2. Write the product by balancing
the charges
3. Check solubility using the rules
4. Label the correct state
5. Balance the reaction
Real World Application
DOUBLE REPLACEMENT
• Soap was synthesized by the Egyptians, Romans, and
Chinese using potassium hydroxide (KOH). Each ancient
civilization used unique procedures to synthesize KOH.
The ancient Chinese made KOH using a doublereplacement reaction.
• Ancient Chinese people heated seashells and then
mixed them with plant ash in water.
(From unknown writer, Kao Gong Ji, ancient Chinese technology cyclopedia, as early as around 732 BCE)
Checking for understanding
Complete the chart
Type of
reaction
1.
2.
3.
4.
5.
General Form
Example
Oxidation vs. Reduction
driven by the loss of electrons (oxidation) and the
gain of electrons (reduction).
Oxidation-Reduction Reaction
• Oxidation is loss of
electrons.
• Reduction is gain of
electrons.
• There is a very easy
way to do this. As
long as you
remember that you
are talking about
electron transfer:
Neutralization
occur when an acid (most compounds starting with H) and
a base (most compounds ending in OH) react to form a
salt and water.
Acid + Base  Salt + Water
H Cl- +
H
O

+
Na
Na+
Cl-
+
O
H
H
General Form: HX + MOH  MX + H2O
where X and M are elements
Checking for understanding
Explain in exactly 10 words each process. Your
sentences do have to make sense:
Oxidation
Reduction
Neutralization
Click Below for the Video Lectures
Molecular, Ionic and Net Ionic
Equations
Synthesis, Decomposition
Reactions
Neutralization Reaction
Redox Reaction