Chapter 9
Chemical Reactions
9.1 Chemical Reactions &
Equations
• Chemical reaction - The process by which
the atoms of one or more substances are
rearranged to form different substances
– Occur when substances go through a
chemical changes
• Evidence of a chemical reaction
– Temperature changes
– Color change
– Odor
– Gas bubbles
– Formation of a solid (precipitate)
Representing Chemical Reactions
• Reactants and Products
• NaHCO3 + HC2H3O2  CO2 + H20 + NaC2H3O2
Symbol
Purpose
Separates two or more reactants or products
Seperates reactants from products
Separates reactants from products and indicates a
reversible reactions
Solid state
Liquid state
Gas state
Water solution (aqueous state)
Word Equations
• Solid aluminum and liquid bromine yield
solid aluminum bromide.
• Solid calcium carbonate and aqueous
hydrochloric acid yield aqueous calcium
chloride, liquid water, and gaseous carbon
dioxide.
Write the Word Equation
• Zn(s) + HCl (aq)  ZnCl2(aq) + H2(g)
• NH3(g) + O2(g)  NO2(g) + H2O (l)
Chemical Equations
• Law of Conservation of Mass =
• Chemical equation – statement that uses
chemical formulas to show the identities
and relative amounts of substances
involved in a chemical reaction
Balancing Chemical Equations
• Law of Conservation of Mass: mass of
reactants must = mass of products
• If I start with 12 g of Carbon I have to end
with 12 g of Carbon
• Each side of the equations must contain
the same number (mass) of atoms
• Balance using COEFFICIENTS – number
written in front of a reactant or product
– Usually whole numbers
– Not written if the value is ne
– Show the lowest whole number ratio of the
amounts of all the reactants and products
• Never ever ever ever ever change the
chemical formulas!!!
• Correct:
– 2H2 + O2  2H2O
• Incorrect:
– H2 + O2  H2O2
How to balance
1. Determine the number of atoms of each
element on reactants and products side.
2. Balance elements one at a time with
coefficients.
3. Make sure the number of atoms on each
side of the equation are equal.
4. Put coefficients in lowest whole number
ratio.
Mg +
O2 
Cu(SO4) +
Al 
MgO
Al2(SO4)3 +
Cu
Challenge!
C2H6 +
O2

CO2 +
H2O
Write the equation and balance
• In water, Iron (III) chloride reacts with
sodium hydroxide producing solid iron (III)
hydroxide and sodium chloride.
9.2 Classifying Chemical Reactions
• There are 5 main types of reactions,
classified according to what happens in
them:
– Synthesis
– Decomposition
– Combustion
– Single Replacement
– Double Replacement
Synthesis Reactions
• 2 or more reactants join to form a single
product
•
•
H2(g) +
CaO(s) +
O2(g) 
H2O(l) 
H2O(l)
Ca(OH)2(s)
Decomposition Reaction
• A single reactant breaks apart
•
H2O(l) 
H2(g) +
O2(g)
• Aluminum oxide decomposes when
electricity is passed through it
Combustion
• Occurs when one of the reactants is
oxygen
•
•
CH4(g)+ O2(g)
SO2 +
O2 
CO2(g) + H2O(l)
SO3
Single Replacement Reactions
• One element replaces the atoms of
another element in a compound
• CuCl2(aq) + Al(s) 
AlCl3(aq)+ Cu(s)
Activity Series
• An element will replace another
element only if it is BELOW it!
• Na + AlCl3
• Cu + ZnCl2
• Br2 + NaF
F
Cl
Br
I
Li
K
Ba
Ca
Na
Mg
Al
Zn
Fe
Ni
Sn
Pb
H
Cu
Hg
Ag
Au
Double Replacement Reactions
• Involves an exchange of ions between two
compounds
• Pb(NO3)2(aq) + 2KI(aq)  PbI2(s)+
2K(NO3)(aq)
• NaCl(aq) + Ag(NO3)(aq)  AgCl(s) +
NaNO3 (aq)
• A solid produced in a double replacement
reaction is called a precipitate
• What are the precipitates from the
previous reactions?
• Double replacement reactions will produce
either water, a precipitate, or a gas
• Predict the products:
• NaOH + CuCl2 
Predicting Products of Chemical
Reactions
1. Decide what type of reaction you have
2. Predict products
3. Balance reaction
• Li +
• HgO 
Cl2 
•
K+
CaO 
•
H2 +
•
Pb(NO3)2 +
KCl 
KI 
9.3 Reactions in Aqueous Solutions
• Double replacement reactions occur
between substances in aqueous solutions
and produce precipitates, water, or gases
• Aqueous solution contains one or more
solutes dissolved in water (the solute)
• When ionic compounds dissolve in water
their ions separate (dissociation)
• NaCl
Types of Reactions in Aqueous
Solutions
• Reactions that form precipitates:
• 2NaOH(aq) + CuCl2 (aq)  2NaCl(aq) + Cu(OH)2 (s)
• Does not show detail of what is happening
in the reaction
Ionic equations
• Substances that are in aqueous solution
are written as ions
• Write the previous chemical equation as
an ionic equation
• Complete ionic equation shows all the
particles in a solution
• Net ionic equations show only the ions that
take part in the reaction
– Atoms that are ions on both sides of the
reaction do not participate in the reaction
(spectator ions)
2NaOH(aq) + CuCl2 (aq)  2NaCl(aq) +
Cu(OH)2 (s)
• Complete ionic equation
• Net ionic equation
Ba(NO3)2(aq) + Na2CO3  BaCO3(s) +
2NaNO3(aq)
• Complete ionic equation:
• Net ionic equation:
Reactions that form water
• HBr(aq) + NaOH(aq)  H2O(l) + NaBr(aq)
• Complete ionic equation
• Net ionic equation
Reactions that form gasses
• 2HI(aq) + Li2S(aq)  H2S(g) + 2LiI(aq)
• Complete ionic equation
• Net ionic equation