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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
)()(2)( 22 sgs MgOOMg
REACTANT(S)REACTANT(S) PRODUCTS(S)PRODUCTS(S)
REACTS REACTS TO FORMTO FORM
Typical Reaction
)()(2)( 22 sgs MgOOMg
CoefficientsCoefficients
SubscriptsSubscripts
PhasesPhases
General Rules
1. Always check your formulas
2. Count the number of each kind of atom.
3. Treat polyatomics like atoms.
4. Put in coefficients to equalize atoms.
5. If an atom appears in more than one place on the same side of the equation, do it last.
6. Do ‘singletons’ LAST…
Balancing EquationsEven-Odd Trick
An odd number x 2 = an even number
K + O2 K2O
Balancing EquationsEven-Odd Trick
Ca + O2 CaO
Balancing EquationsTwo’s and Three’s
N2 + H2 NH3
Balancing EquationsTwo’s and Three’s
Al + Cl2 AlCl3
Balancing EquationsPAI’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 EquationsPAI’s
Ca(NO3)2 + Na2S CaS + NaNO3
Balancing EquationsPAI’s
Ca(NO3)2 + Na2SO4 CaSO4 + NaNO3
Balancing EquationsPAI’s
AlBr3 + SrCO3 Al2(CO3)3 + SrBr2
Balancing EquationsPAI’s
Fe(NO3)3 + (NH4)2CO3 Fe2(CO3)3 + NH4NO3
Balancing EquationsPAI’s
AgNO3 + K2CrO4 Ag2CrO4 + KNO3
Balancing EquationsC, H, O
Balance in order C then H then O
CCan’t HHave OOrder
Balancing EquationsC, H, O
CH4 + O2 CO2 + H2O
Balancing EquationsC, H, O
C2H6 + O2 CO2 + H2O
C2H6 + O2 CO2 + H2O
To get whole number coefficients =
Must get rid of the fraction so you times all coefficients by 2
Balancing EquationsC, H, O
C4H10 + O2 CO2 + H2O
C4H10 + O2 CO2 + H2O
Balancing EquationsC, H, O
C24H50 + O2 CO2 + H2O
C24H50 + O2 CO2 + H2O
Tricky Question #18
Ca(OH)2 + NH4Cl NH3 + CaCl2 + H2O
Balancing EquationsC, H, O- alcohols
CH3OH + O2 CO2 + H2O
Balance These
C14H29OH + O2 CO2 + H2O
C6H12O6 + O2 CO2 + H2O
C9H50O4S2 + O2 CO2 + SO2 + H2O
Worksheet
Do Problem Set #1 on page 4 in your Student Workbook
