Chemical Reactions
I.
Intro to Reactions
I
II III IV V
A.Signs of a Chemical Reaction
Evolution of heat and light
 Formation of a gas
 Formation of a precipitate
 Color change

B.Law of Conservation of Mass

mass is neither created nor destroyed
in a chemical reaction
total mass stays the same
 atoms can only rearrange

4H
36 g
2O
4H
2O
4g
32 g
C. Chemical Equations
A+B  C+D
REACTANTS
PRODUCTS
C. Chemical Equations
(substance dissolved in water)
Pt
a catalyst is present (in this case, platinum)
Diatomic Elements

H2, N2, O2, F2, Cl2, Br2, and I2
II. Balancing Equations
I
II III IV V
A. Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients to make #s equal.
Note: you may not change a subscript
Coefficient  subscript = # of atoms
4. Reduce coefficients to lowest
possible ratio, if necessary.
B. Helpful Tips
Balance one element at a time.
 If an element appears more than
once per side, balance it last.
 Balance polyatomic ions as single
units.
 “1 SO4” instead of “1 S” and “4 O”

C. Balancing Example
Aluminum and copper(II) chloride react
to form copper and aluminum chloride.
2 Al + 3 CuCl2  3 Cu + 2 AlCl3
2 1
Al
1 2
3 1
Cu
1 3
6 2
Cl
3 6
Balancing
Equations
C3H8(g) + O2(g) ----> CO2(g) + H2O(g)
B4H10(g) + O2(g) ----> B2O3(g) + H2O(g)
Balancing Equations
Sodium phosphate and iron (III)
oxide react to form sodium oxide
and iron (III) phosphate
Na3PO4 + Fe2O3 ----> Na2O + FePO4