Chapter 13 Chemical Equilibrium
How far does a reaction proceed toward the completion before it reaches a
state of chemical equilibrium – a state in which the concentrations of
reactants and products no longer change?
Chemical reactions can occur in both forward and reverse directions, and
when the rates of the forward and reverse reactions become equal, the
concentrations of reactants and products remain constant.
o Chemical system is at equilibrium
Mixture of reactants and products in the equilibrium state is called an
13.1 The Equilibrium State
Previous chapter chemical reactions result in complete conversion of
reactants and products.
o Many reactions, however do not go to complete
All chemical reactions are reversible.
o Irreversible reactions are simple those that proceed nearly to
completion, so that the equilibrium mixture contains almost all
products and almost no reactants
For such reactants, the reverse reaction is often too slow to be
Concentrations reach constant values, not because the reactions stop, but
because the rates of the forward and reverse reaction become equal.
N O2i4 converted to an equilibrium mixture of NO and N2O 2 4
Because reaction rates depend on concentrations, the
rate of the forward reaction (N O242NO ) de2reases as
the concentration of N O2d4creases, while the rate of