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
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