Chemical Reactions and Chemical Equations
A chemical reaction is a process in which one set of substances (reactants) is
converted to a new set of substances (products). The main evidences that prove
that a chemical reaction has occurred are:
a) Colour change
b) Formation of a solid (precipitate) within a clear solution
c) Evolution of a gas
d) Evolution or absorption of heat
To write the shorthand representation of a chemical equation certain steps must be
followed. Consider the chemical reaction: nitrogen monoxide + oxygen nitrogen
1. Write the reaction using chemical symbols
NO + O 2NO 2
2. Balance the chemical equation
2NO + 1O2 2 NO2
*** Balancing equations***
Remember these rules when balancing an equation
1. An equation can be balanced only by adjusting the coefficients of formulas.
2. Never introduce extraneous atoms to balance.
NO + O 2NO + O2
3. Never change a formula for the purpose of balancing an equation.
NO + O 2NO 3
When balancing equations, using these strategies will result in efficient balancing of
Balance elements that occur in only one compound of each side first.
Balance free elements last.
Balance unchanged polyatomics (or other groups of atoms) as groups.
Fractional coefficients are acceptable and can be cleared at the end by
multiplication. Problem: Balance C H O 6 O14 4O + H2O 2 2
Balance C: C H 6 +14 4 6 CO2+ H O 2 2
Balance H: C H 6 +14 4 6 CO2+ 7H O 2 2
At this point, the right side contains 19 O atoms whereas the left only contains 4. To
get 15 more O atoms we need to add 15/2 more O atoms by multiplying it with O . 2
Balance O: C H 6 14(14/2) O 6 CO 2 7H O 2 2
Now remove the fraction by multiplying the whole equation by 2.
2C 6 O14 14 O 12 2O + 1