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Chapter 10
Chemical Reactions
Evidence of Chemical Change
A chemical reaction is a process by which
the atoms of one or more substances are
rearranged to form different substances.
4 Indicators
Change in color
Change in temperature or energy
Production of a gas
Formation of a precipitate
Representing Balanced Chemical Equations
Reactants
Product
2 H 2( g )  O2( g )  2 H 2O(l )
Coefficient
Subscript
Physical state
Symbols
+
Separates two or more products or reactants
Separates reactants from products
(s) Solid
(l) Liquid
(g) Gas
(aq) Aqueous
Writing Chemical Equations
Iron combines with oxygen to form solid iron (III) oxide
4Fe( s )  3O2( g )  2Fe2O3( s )
 All metals are represented by their symbol in the periodic
table with NO subscripts.
 All elemental gases are diatomic (BrINClHOF)
 Use your ion table or molecular name to figure out the
chemical formula of compounds in your equation
 Balance the equation
 Note the physical state of each substance in the equation
Practice Problem
Aqueous calcium chloride combines with aqueous
silver nitrate to form aqueous calcium nitrate and
solid silver chloride.
Another Practice Problem
Aluminum combines with aqueous hydrochloric
acid (HCl) to form aqueous aluminum chloride and
hydrogen gas.
Hint: Write the formula for each substance as if it were
independent of the other substances in the equation.
Balancing Chemical Equations
A written chemical equation must abide by
the law of conservation of matter
Make sure that both sides of an equation
have an equal number of each type of atom
represented.
Balance equations by adding coefficients.
Never mess with subscripts
Examples
__ NaCl  __ MgBr2  __ MgCl2  __ NaBr
Na
Cl
Mg
Br
__ Mg  __ FeCl3  __ MgCl 2  __ Fe
Mg
Fe
Cl
Strategies for Balancing Chemical
Equations
1. The even/odd combination
Make the subscript of one, the coefficient of the
other and vice versa.
Iron (III) oxide
Iron + Oxygen
2Fe2 03  4Fe  3O2
Strategies Continued
2. Balance groups as a whole if the elements
of the group are only represented in the
group on each side of the equation.
__ Mg (OH ) 2  __ Al  __ Al (OH )3  __ Mg
Mg
OH
Al
Strategies Continued
3. Balancing Hydrocarbon Combustion Reactions
The first step is to add a coefficient to the hydrocarbon so
that the total number of hydrogens in the molecule is
divisible by four. Then, balance the product side of the
equation before finishing up with oxygen.
__ CH 5  __ 02  __ CO2  __ H 2 0
C
H
O
Strategies Continued
4. Splitting Water
When hydroxide shows up on one side of an
equation and water is on the other side, split water
into H(OH) to balance out hydroxide.
__ Mg (OH ) 2  __ H 2 SO3  __ MgSO3  __ H 2O
Things to Keep in Mind
Again, do not mess with subscripts
In the final solution, the coefficients have
to be in the lowest whole number ratio.
4H 2  2O2  4H 2O
2H 2  O2  2H 2O
If at first you don’t succeed, try, try again!
Most of the solutions to these problems
come from trial and error.
Practice Problem
 Write the equation
 Note the physical state of each substance
 Balance the equation
Potassium chromate combines with lead (II) nitrate to form
potassium nitrate and lead (II) chromate
Types of Chemical Reactions – 5 General
Formulas
Combustion
CxHy + O2
CO2 + H20
Always the products of these
combustion reactions
Synthesis
A+B
AB
(Two elements combine to form a compound)
Decomposition
AB
A+B
(One compound splits to form two compounds)
Reactions Cont.
Single Replacement (Single Displacement)
A + BC
AC + B Metals replace metals
Non-metals replace non-metals
Double Replacement (Double Displacement)
AB + XY
AY + XB Compounds switch partners
Pre-class Question 3/25
Combustion
Decomposition
Synthesis
Single replacememt
Double Replacement
Identify the type of reaction
3Ba ( s )  Fe2 ( SO4 ) 3( aq)  2 Fe( s )  3BaSO4 ( s )
2C4 H10( g )  13O2 ( g )  8CO2 ( g )  10 H 2 0( l )
2 Mg ( s )  O2 ( g )  2 MgO( s )
CaCl2 ( aq)  Li2CrO4 ( aq)  CaCrO4( s )  2 LiCl( aq)
2 Fe2O3( s )  4 Fe( s )  3O2 ( g )
Predicting Products of Hydrocarbon
Combustion Reactions
With hydrocarbons, the products are
always CO2 (g) and H2O(l)
_ C8 H18( g )  _ O2( g ) 
Predicting Products of Synthesis
Reactions
For Synthesis Reactions
For metals that only form one cation, determine the
charge on the ion of each element (metallic and nonmetallic) and form a compound from the two ions.
If one of the elements forms more than one cation or
2 nonmetals are combined, the products can only be
predicted if the ratio of elements in the compound are
given
Ag( s )  Cl2 ( g ) 
Predicting Products of Decomposition
Reactions
HCl (aq ) 
Predicting Products of Double
Replacement Reactions
• Rearrangement of cations and anions to form 2
new compounds.
• Reaction occurs when a solid or water is
produced from aqueous reactants
MgCl2( aq)  Li3 PO4( aq) 
Predicting Products of Single
Replacement Reactions
 Refer to the activity series chart to determine if
the reaction will occur.
 Metals replace metals. Nonmetals replace nonmetals
Cl2 ( g )  CaBr2 ( aq) 
Na( s )  AlCl3( aq) 
Physical States
Atoms
Metals – All solid except mercury (liquid)
Nonmetals – all diatomic gases except bromine
(liquid) and iodine (solid)
Compounds
Covalent compounds – usually a liquid or gas,
but not predictable
Acids – always aqueous (aq)
Ionic compounds – refer to solubility table
Soluble (dissolves) – aqueous (aq)
Insoluble (doesn’t dissolve) – solid (s)
Using a solubility Table for Ionic
Compounds
NaCO3
General Rules Table
• Look up the solubility for a compound’s anion
Common Ion
Solubility
Exceptions
CO32-
insoluble
Group IA and NH4+
• If the substance is insoluble then it is a solid
• If the substance is soluble it is aqueous
• Check to see if the cation in your compound is in the
exception column.
Final Answer: NaCO3(aq)
Determine the physical states
CaSO4
Solid
(NH4)2S
Aqueous
K3PO4
Aqueous
CuC2H3O2 Aqueous