BALANCING EQUATIONS
Balanced equations obey the law of conservation of mass.
The total mass before a reaction takes place will equal the total mass after the reaction is complete.
The number of atoms which take part in a chemical reaction will also remain constant.
Balancing an equation can sometimes involve trial and error. The following
rules and suggestions can
go a long way in keeping down the errors.
1. The equation will be understood to proceed from left to right. The
reactants are on the left side of
the arrow and the products are on the right.
2 H2 + O2 ----> 2 H2O
Reactants
Products
2. Equations are balanced by adjusting COEFFICIENTS in front
of formulas, never by changing
subscripts within formulas. Remember that
a 1 is understood when a coefficient is not present.
3. It is best to start with an element that appears in only one compound on each side of the arrow.
4. Next balance any element that appears in more than one compound on either the right or left.
5. Balance free elements last. That is balance any element that appears
in elemental form on the
right or left.
6. When polyatomic species (NH4+, SO4-2,
OH-, etc.) appear on both sides of the arrow in
compounds or as ions, balance them as units rather
than individual elements.
7. Leave the coefficients in the lowest whole number ratio.
EXAMPLE 2
C2H8N2
+ N2O4 ---->
N2 + H2O
+ CO2
EXAMPLE 3
Fe2(SO4)3
+ BaCl2 ---->
BaSO4 + FeCl3
EXAMPLE 4
H3PO4 +
Ca(OH)2 ----> Ca3(PO4)2
+ H2O
COMBUSTION REACTIONS
Combustion is a chemical reaction in which a substance reacts with
oxygen, usually with the
rapid release of heat to produce a flame. We will limit our discussion
to the complete combustion
of hydrocarbons. Hydrocarbons react (combust) with oxygen
to yield carbon dioxide and water.
EXAMPLE 5
CH4(g) +
O2(g) ---> CO2(g)
+ H2O(g)
EXAMPLE 6
C2H6(g) +
O2(g) ---> CO2(g)
+ H2O(g)
EXAMPLE 7
C4H10(g) +
O2(g) ---> CO2(g)
+ H2O(g)