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Chapter 21
Section 2
• A balanced equation is one that has the same
number of atoms on one side as it does the
other.
• You use coefficients to help you balance an
equation.
• Once balanced make sure it is in simplest
terms possible.
• HgO(s)
Hg(l) + O2 (g)
4 steps to help you balance
• Write the chemical equation for the reaction
using formulas and symbols. (Remember oxygen
is a diatomic molecule, and if by itself will always
be O2 )
• Count the reactants and products.
• Choose coefficients that balance the equation.
Remember, NEVER change subscripts of a correct
formula to balance an equation.
• Recheck the numbers of each atom on each side
of the equation and adjust the coefficients again
as needed.
• Al + O2
Al2 O3
• HgO
Hg + O2
• NaOH + H2 SO4
Na2 SO4 + H2 O
• Fe + O2
Fe2 O3
• Pb (NO3 )2 + K2 CrO4
PbCrO4 + KNO3