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