CHEMICAL EQUATIONS
Chemical Equation:
Represents, with symbols and formulas, the
identities and relative molecular or molar
amounts of the reactants and products in a
chemical reaction.
Chemical Equation:
Identities and relative amounts of the reactants
and products
COMPONENTS OF CHEMICAL EQUATIONS
Al (s) + O2 (g)  Al2O3 (s)
Reactants  Products
Reactants:
“Ingredients”, what you start with, left
Products:
“final materials”, what you end up with, right
COMPONENTS OF CHEMICAL EQUATIONS
CHEMICAL EQUATIONS INTO WORDS
C (s) + O2 (g)  CO2 (g)
Solid carbon plus oxygen gas react to yield
carbon dioxide gas
COEFFICIENTS AND SUBSCRIPTS
4 Al (s) + 3 O2 (g)  2 Al2O3 (s)
Coefficient: Number in front, tells the number of
molecules
Subscript: Number below, tells the number of
atoms of an element in each molecule
COEFFICIENTS AND SUBSCRIPTS
COEFFICIENTS AND SUBSCRIPTS
4 Al (s) + 3 O2 (g)  2 Al2O3 (s)
COEFFICIENTS AND SUBSCRIPTS
Ca(OH)2
Subscripts outside of parentheses apply to everything inside
the parentheses
How many oxygens are present in each of the following?
1. NaOH
2. Ca(OH)2
3. 3 Ca(OH)2
LAW OF CONSERVATION OF MATTER
Matter cannot be created nor destroyed
LAW OF CONSERVATION OF MATTER
Because of the law of conservation of matter, an
equation must be balanced!
Equations must have the same number of atoms
of each element on both sides of the equation
BALANCING EQUATIONS
Skeleton Equation: Unbalanced equation, an
equation without coefficients
Balanced Equation: The number of atoms of
each element are equal on both sides
BALANCING EQUATIONS
When balancing chemical reactions you may
add coefficients in front of the compounds to
be balanced, but you may
subscripts
not change the
Changing subscripts changes the compound.
Subscripts are determined by the valance
electrons (charges for ionic or electrons shared
for covalent)
BALANCING EQUATIONS
Mg + O2  MgO
BALANCING EQUATIONS
___ C3H8 (g) + ___ O2 (g)  ___ CO2 (g) + ___ H2O (g)
BALANCING EQUATIONS
a) ___ Mg + ___ HCl  ___ MgCl2 + ___ H2
b) ___ Ca + ___ N2  ___ Ca3N2
c) ___ NH4NO3  ___ N2O + ___ H2O
BALANCING EQUATIONS
d) BiCl3 + H2S  Bi2S3 + HCl
e) C4H10 + O2  CO2 + H2O
f) O2 + C6H12O6  CO2 + H2O
g) NO2 + H2O  HNO3 + NO
h) Cr2(SO4)3+ NaOH  Cr(OH)3+ Na2SO4
i)
Al4C3 + H2O  CH4 + Al(OH)3
BALANCING EQUATIONS
d) 2 BiCl3 + 3 H2S  1 Bi2S3 + 6 HCl
e) 2 C4H10 + 13 O2  8 CO2 + 10 H2O
f) 6 O2 + 1 C6H12O6  6 CO2 + 6 H2O
g) 3 NO2 + 1 H2O  2 HNO3 + 1 NO
h) 1 Cr2(SO4)3+ 6 NaOH  2 Cr(OH)3+ 3 Na2SO4
i)
1 Al4C3 + 12 H2O  3 CH4 + 4 Al(OH)3
BALANCING EQUATIONS
Back side of the worksheet is your homework!
STEPS TO BALANCE EQUATIONS
1. Write the correct formula for the reactants and the
products. (Do not change the formula in later steps)
2. Find the number of atoms for each element on both
sides
3. Determine where to place coefficients in front of
formulas so that each element has the same number
of atoms on both sides
4. Check your answer to see if:
• Equation is balanced
• Coefficients are in the lowest possible whole
number ratios (reduced)