1. Unit 3. Chemical Reactions 3.3 How do we balance a chemical reaction?
February 8, 2010
AIM: How do we balance chemical reactions in order to obey the law of conservation of mass?
DO NOW: MR #3 An element that has a low first ionization energy and good conductivity of heat and electricity is classified as a
(1) metal (3) nonmetal
(2) metalloid (4) noble gas J
CHOICE
LOW IONIZATION ENERGY?
GOOD CONDUCTIVITY OF HEAT AND ELECTRICITY?
METAL
NONMETAL
METALLOID
NOBLE GAS
Check the TABLE S
LOW
YES
THINK: copper wires
Periodic Trends?
HIGH NO
SOME HIGH SOME LOW
SOME YES SOME NO
These are nonmetals already….don’t waste your time!

2. HOW DO WE BALANCE EQUATIONS?
C(s) + O2(g) → CO2(g)
Step 1. Check that an equal amount of an element
appears in the reactants that does in the products
Element
Reactants
Products C 1 1 O 2 2
Step 2. If not equal add coefficients
THIS IS A
BALANCED
EQUATION
Step 3. Check that the equation is balanced
after you add coefficients.

3. LET’S TRY SOME 2 x 2 = 4 2 x 2 = 4 2 1 x 2 = 2 H2(g) + O2(g) → H2O(g)
Element
Reactants
Products H O 2
x 2
= 4 2
x 2
= 4 2 1
x 2
= 2
Not equal so we must add COEFFICIENTS!

4. LET’S TRY SOME 1 x 2 = 2 1 1 x 2 = 2 1 3 x 2 = 6 2 x 3 = 6 2 2 3 x 2
KClO3  KCl + O2 3
Reactants
Products K Cl O 1
x 2
= 2 1
x 2
= 2 1
x 2
= 2 1
x 2
= 2 3
x 2
= 6 2
x 3
= 6

5. Complete the Independent Practice
-IP will be collected at the end of class!!!
WORK ON UNIT 1 in your HOMEWORK PACKET
UNIT 1 completion will be check on Monday at the beginning of class