http://www.ck12.org Chapter 11. Chemical Reactions
or the net change that occurs after multiple sequential chemical processes.
The Balanced Chemical Equation
We can describe chemical reactions in terms of generic expressions like the following equation:
aA+bB→cC+dD
whereAandBare reactants, andCandDare products. The lettersa,b,c, anddrepresentstoichiometric
coefficients, or the relative amount of each substance that is involved in the reaction. In this particular reaction,
there are two reactants and two products, but others might have more or less. For example, the equation describing
the rusting of iron had two reactants (Fe and O 2 ) and one product (Fe 2 O 3 ).
In abalanced chemical equation, the number of atoms of each element on the reactant side is equal to the number
of atoms on the product side. This is necessary for all chemical equations, due to the law of conservation of mass.
Atoms are neither created nor destroyed during a chemical reaction, only rearranged. Here are some examples of
general expressions that will be applied to specific reactions in the next section.
Example 11.1
Substance A reacts with substance B to form substance AB. Write the balanced chemical equation for this process.
Answer:
Write the general expression.A+B→AB
Balance (it already is).TABLE11.2: A + B→AB
Reactants Products
A 1 1
B 1 1Example 11.2
Substance A reacts with substance B 2 to form substance AB. Write the balanced chemical equation for this process.
Answer:
Write the general expression.A+B 2 →AB
Balance.2 A+B 2 → 2 AB
TABLE11.3:Example 11.2
Reactants Products
A 2 2
B 2 2