Download Chemical Equations

Chemical Equations
Describing Chemical Process
Chemical Equations
 Identify the substances involved in a
chemical process
 Distinguish between the reactants and
products in a chemical process
 Allow easy determination of quantities of
substances involved in chemical processes
Verbal description of a common
chemical process:
“Methane undergoes combustion in
oxygen to form carbon dioxide and
water.”
The substances:




methane: CH4
Oxygen: O2
Carbon dioxide: CO2
Water: H2O
The form of an equation:
Reactant(s)
Product(s)
The form of an equation:
Reactant(s)
One or more
substances -the beginning
“stuff”
Product(s)
The form of an equation:
Reactant(s)
One or more
substances -the beginning
“stuff”
Product(s)
Reaction
arrow; points
toward the
product(s)
The form of an equation:
Reactant(s)
One or more
substances -the beginning
“stuff”
Product(s)
Reaction
arrow; points
toward the
product(s)
One or more
substances -the final
“stuff”
For the reaction of methane:
CH4 + O2  CO2
Methane
Carbon
Water
dioxide
The reaction
Products
arrow
Oxygen
Reactants
+ H2O
For the reaction of methane:
CH4 + O2  CO2
+ H2O
H
O=O
H
C
O=C=O
O
H
H
H
H
For the reaction of methane:
CH4 + O2  CO2
+ H 2O
H
H
O=O
C
O=C=O
O
H
H
4 H atoms, 2
H
oxygen atoms
H
2 H atoms, 3 oxygen atoms
Note, there appear to be more oxygen atoms, fewer
hydrogen atoms at the end that at the beginning!
For the reaction of methane:
CH4 + O2  CO2
+ 2 H2O
H
O=O
H
C
O=C=O
O
O
H
H
H
H
H
There are enough H atoms in one methane molecule to
make two water molecules.
…but, oxygen is worse off!
H
For the reaction of methane:
CH4 + 2 O2  CO2
+ 2 H2O
H
O=O
H
C
H
H
O=O
O=C=O
O
H
H
O
H
Adjust the total number of oxygen atoms with more
O2. Now, oxygen is OK.
H
For the reaction of methane:
CH4 + 2 O2  CO2
+ 2 H2O
H
O=O
H
C
H
H
O=O
O=C=O
O
H
H
O
H
All atoms are in the same numbers before and after.
H
Propane reacts similarly with O2
C3H8 + O2  CO2
+ H 2O
Propane
None of the atoms appear in the same amounts before
and after; the equation is UNBALANCED.
Propane reacts similarly with O2
C3H8 + O2  CO2
+ H 2O
None of the atoms appear in the same amounts before
and after; the equation is UNBALANCED.
There are enough H atoms in one propane molecule to
make four water molecules.
Propane reacts similarly with O2
C3H8 + O2  CO2
+ 4 H2O
Hydrogens are OK, but carbons are unequal before
and after, still.
There are enough carbon atoms in propane to make
three carbon dioxide molecules.
Propane reacts similarly with O2
C3H8 + O2  3 CO2
+ 4 H2O
Carbons are OK, but oxygen atoms are still unequal
before and after.
Adjust the total number of oxygen molecules...
Propane reacts similarly with O2
C3H8 + 5 O2  3 CO2
+ 4 H2O
Now, all atoms are equal in number before and after.
The equation is BALANCED.
Propane reacts similarly with O2
C3H8 + 5 O2  3 CO2
+ 4 H2O
Now, all atoms are equal in number before and after.
The equation is BALANCED.
A “picture” of this reaction:
C3H8 + 5 O2  3 CO2
H
H
C
C
H
H
H
C
HH
H
+ 4 H2O
A “picture” of this reaction:
C3H8 + 5 O2  3 CO2
H
H
C
C
H
H
H
O=O
C
H O=O
O=O
HH
O=O
O=O
+ 4 H2O
A “picture” of this reaction:
C3H8 + 5 O2  3 CO2
H
H
C
C
H
H
H
O=O
C
H O=O
O=O
HH
O=O
O=O
O=C=O
O=C=O
O=C=O
+ 4 H2O
A “picture” of this reaction:
C3H8 + 5 O2  3 CO2
H
H
C
C
H
H
H
O=O
C
H O=O
O=O
HH
O=O
O=O
O=C=O
O=C=O
O=C=O
+ 4 H2O
H
H
H
H
O
H
O
O
O
H
H
H
Suggestions to Balance
Equations
 Work with elements that appear in the fewest
formulas first (in one formula on “each side”
of the reaction arrow.
 Proceed to elements appearing in greater and
greater numbers of formulas.
 Always check to see that elements are in
same numbers on both sides.
Practice
C6H12O6 + O2  H2O + CO2
Practice
C6H12O6 + O2  H2O + CO2
Start with either C or H. Oxygen appears
in every formula; save it till last.
Practice
C6H12O6 + O2  H2O + 6 CO2
There are enough C atoms in C6H12O6 to
form six CO2 molecules.
Practice
C6H12O6 + O2  6 H2O + 6 CO2
There are enough H atoms in C6H12O6 to
form six H2O molecules.
Practice
Six O atoms
Twelve O atoms,
6 sets of two
C6H12O6 + 6 O2  6 H2O + 6 CO2
Twelve O atoms
Six O atoms
Six O2 molecules are required to provide
enough total oxygen atoms to balance.
Check
18 total O atoms
18 total oxygen atoms
C6H12O6 + 6 O2  6 H2O + 6 CO2
Check
12 H atoms
12 total H atoms
C6H12O6 + 6 O2  6 H2O + 6 CO2
Check
six C atoms
six C atoms
C6H12O6 + 6 O2  6 H2O + 6 CO2
Your turn...
Al2O3 +
H2 
H2O +
Al
Your turn...
1 Al2O3 + 3 H2  3 H2O + 2 Al
Your turn...
Al2O3 + 3 H2  3 H2O + 2 Al
Check:



2 Al atoms
3 Oxygen atoms
6 H atoms



2 Al atoms
3 Oxygen atoms
6 H atoms
Your turn...
Ca(OH)2 +
HCl 
H2O +
CaCl2
Your turn...
1 Ca(OH)2 + 2 HCl  2 H2O + 1 CaCl2
Your turn...
Ca(OH)2 + 2 HCl 
2 H2O +
Check:




1 Ca atom
2 oxygen atoms
2 chlorine atoms
4 hydrogen atoms




1 Ca atom
2 oxygen atoms
2 chlorine atoms
4 hydrogen atoms
CaCl2
Your turn...
H2O +
Mg3N2 
Mg(OH)2 +
NH3
Your turn...
6 H2O + 1 Mg3N2  3 Mg(OH)2 + 2 NH3
Your turn...
6 H 2O +
Mg3N2  3 Mg(OH)2 + 2 NH3
Check:




12 H atoms
six O atoms
3 Mg atoms
2 N atoms




12 H atoms
six O atoms
3 Mg atoms
2 N atoms
Your turn...
NH3 +
O2 
NO
+
H2O
Your turn...
4 NH3 + 5 O2
 4 NO
+ 6 H2O
Your turn...
4 NH3 + 5 O2
 4 NO
+ 6 H2O
Check:



4 N atoms
12 H atoms
10 oxygen atoms



4 N atoms
12 H atoms
10 oxygen atoms