Chemical reactions result in chemical changes where reactants change into new products. Chemical reactions can be written with word equations or symbolic equations. A balanced chemical equation shows that the number of each type of atom is the same on both sides of the reaction, ensuring the law of conservation of mass is followed. Balancing chemical equations involves determining the coefficients needed for the number of atoms to be equal on both sides.

1. • Chemical reactions result in chemical
changes.
– Chemical changes occur when new substances
are created.
– The original substance(s), called reactants,
change into new substance(s) called products.
(c) McGraw Hill Ryerson 2007
See pages 202 - 203

2. (c) McGraw Hill Ryerson 2007
See pages 202 - 203

3. • Chemical reactions can be written in different
ways.
– A word equation:
• Nitrogen monoxide + oxygen → nitrogen dioxide
– A symbolic equation:
• 2NO(g) + O2(g) → 2NO2(g)
COEFFICIENTS
STATE OF MATTER
- Letters indicate the state of
each compound.
(aq) = aqueous/dissolved in
water
- Indicates how many of each
molecule there is.
(s) = solid
-Ie: there are 2 molecules of NO.
(g) = gas
(c) McGraw Hill Ryerson 2007
( ) = liquid

4. • When a chemical reaction occurs, new compounds are
created, BUT…
– No new matter is created or destroyed; atoms are
destroyed
just rearranged as the atoms change partners to form
new compounds.
– If there are 3 atoms of oxygen in the reactants, there
MUST be 3 atoms of oxygen in the products.
– Number of each atom in reactants = number of each
atom in products.
• The law of conservation of mass:
– Mass of reactants = mass of products
If you could collect and measure all of the exhaust from
this car, you would find that mass of reactants (gas + O2) =
mass of products (exhaust).
(c) McGraw Hill Ryerson 2007

5. • A balanced chemical equation shows all
atoms and the coefficients tells us how many
molecules (and atoms) there are.
– Balancing ensures that the number of each
atom is the same on both sides of the reaction
arrow.
4K
K K
K K
+
O2
O O
→
2K2O
K O K
K O K

6. Skeleton equation:
The same number
of atoms must be on
each side.
Balanced equation:
CH4 + O2 → H2O + CO2
Carbon = 1
Hydrogen = 4
Oxygen = 2
Carbon = 1
Hydrogen = 2
Oxygen = 3
CH4 + 2O2 → 2H2O + CO2
Carbon = 1
Hydrogen = 4
Oxygen = 4
(c) McGraw Hill Ryerson 2007
Carbon = 1
Hydrogen = 4
Oxygen = 4
See Page 207

7. Balancing Equations
hydrogen
+ oxygen
H2 +
H
O
O2


water
H2O
Reactants
2
Products
2
2
1

8. Balancing Equations
+ oxygen

hydrogen peroxide
X
hydrogen
H2 +
O2

H2O2
YOU CANNOT CHANGE THE SUBSCRIPTS
H
O
Reactants
2
2
Products
2
2

9. Balancing Equations
hydrogen
+ oxygen
H2 +
H
O
O2
Reactants
2
2

water
 2H2O
Products
2
1

10. Balancing Equations
hydrogen
+ oxygen
H2 +
H
O
O2
Reactants
2
2

water
 2H2O
Products
4
2

11. Balancing Equations
hydrogen
+ oxygen
2 H(g) +
2
H
O
O2
Reactants
4
2
(g)

water
 2H2O
(l)
Products
4
2

12. http://www.authorstream.com/Presentation/kellymdeters-86103-section-2-7-balancin

13. • Balance the following:
– ____Fe + ____Br2 → _____FeBr3
Sn(NO2)4 +
C2H6 +
K3PO4 →
O2 →
KNO2 +
CO2 +
H2O
Sn3 (PO4)4

14. ____Ba + ____H2O
____CO2 + ____H2O
→
→
____Ba(OH)2 + ____H2
____H2CO3
____Fe2O3 + ____C
→
____Fe + ____CO
____Fe + ____H2O
→
____H2 + ____Fe2O3