Download Unit VI: CHEMICAL REACTIONS

Unit I: CHEMICAL
REACTIONS
I.5. Balancing Chemical
Equations
Chemical Equations

Remember:

Formulas must BE CORRECT

Ionic – use charges



the crisscross method
look at net overall charge
Covalent [molecular] – use prefixes
Phases

Sometimes a chemical reaction will
also show the phases in which the
reactants and products exist
 (s) – solid
 (l) – liquid
 (g) – gas
 (aq) – aqueous (water solution)
Typical Reaction
2Mg ( s )  O2( g )  2MgO( s )
REACTANT(S)
REACTS
TO FORM
PRODUCTS(S)
Typical Reaction
Phases
2Mg ( s )  O2( g )  2MgO( s )
Subscripts
Coefficients
General Rules
1.
2.
3.
4.
5.
6.
Always check your formulas
Count the number of each kind of atom.
Treat polyatomics like atoms.
Put in coefficients to equalize atoms.
If an atom appears in more than one place
on the same side of the equation, do it last.
Do ‘singletons’ LAST…
Balancing Equations
Even-Odd Trick

An odd number x 2 = an even number
K
+
O2 
K2 O
Balancing Equations
Even-Odd Trick
Ca
+
O2 
CaO
Balancing Equations
Two’s and Three’s
N2
+
H2 
NH3
Balancing Equations
Two’s and Three’s
Al +
Cl2 
AlCl3
Balancing Equations
PAI’s



Trick is to look for a PAI on both sides
of the equation
A PAI can be thought of as a single
“thing”
Start with the most complex compound
Balancing Equations
PAI’s
Ca(NO3)2 +
Na2S 
CaS +
NaNO3
Balancing Equations
PAI’s
Ca(NO3)2 + Na2SO4 
CaSO4 + NaNO3
Balancing Equations
PAI’s
AlBr3 +
SrCO3 
Al2(CO3)3 + SrBr2
Balancing Equations
PAI’s
Fe(NO3)3 +
(NH4)2CO3 
Fe2(CO3)3 + NH4NO3
Balancing Equations
PAI’s
AgNO3 +
K2CrO4 
Ag2CrO4 +
KNO3
Balancing Equations
C, H, O

Balance in order

C then H then O

Can’t Have Order
Balancing Equations
C, H, O
CH4
+
O2 
CO2 +
H2O
Balancing Equations
C, H, O
C2H6 +
O2 
CO2 +
H2O
To get whole number coefficients =
Must get rid of the fraction so you times all coefficients by 2
C2H6 +
O2 
CO2 +
H2O
Balancing Equations
C, H, O
C4H10
+
O2 
CO2 +
H2O
C4H10
+
O2 
CO2 +
H2O
Balancing Equations
C, H, O
C24H50
+
O2 
CO2 +
H2O
C24H50
+
O2 
CO2 +
H2O
Tricky Question #18
Ca(OH)2
+ NH4Cl 
NH3 + CaCl2 + H2O
Balancing Equations
C, H, O- alcohols
CH3OH
+
O2 
CO2 +
H2O
Balance These
C14H29OH
C6H12O6
C9H50O4S2
+
+
O2 
O2 
CO2 +
CO2 +
H2O
H2O
+ O2  CO2 + SO2 + H2O
Worksheet

Do Problem Set #1
on page 4 in your
Student Workbook