Chapter 5
Chemical equilibrium and
acids-bases equilibria
5
, Chemical Equilibrium: What Is It All About?
• To ―correct‖ imbalance, a spontaneous flow or transfer from high to low occurs.
• Imbalances can be due to differences in
– concentration,
– pressure,
– energy, or
– temperature.
• Once the imbalance has been rectified, the system is said to be at equilibrium.
• Systems at equilibrium are dynamic in nature and reversible.
– Dynamic: condition in which the forward rate of the reaction is equal to the
reverse rate of the reaction
– Example: A system at equilibrium is one in which the concentrations of
reactants and products remain constant.
• The rates at which the substances are being consumed and made are
the same.
Instructor’s Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach , 3/e, Global Edition © 2016 Pearson Education, Ltd.
Nivaldo J. Tro
, Chemical Equilibrium Does Not Mean Equal
Quantities
• At equilibrium, the forward (kf) and reverse (kr) rates of reactions
are equal.
– kf = kr does not mean that the amounts of reactants and
products are equal.
• Reactions may reach equilibrium only after most of the reactant
molecules have been consumed.
– This indicates that the position of equilibrium favors the
formation of products.
• Reactions may reach equilibrium after only a small percentage of
the reactant molecules has been consumed.
– This indicates that the position of equilibrium favors the
reactants.
Instructor’s Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach , 3/e, Global Edition © 2016 Pearson Education, Ltd.
Nivaldo J. Tro
, Chemical Reaction Dynamics
• At the very beginning of a chemical reaction, the forward reaction rate is
favored:
– Reactants → product formation dominates.
• The reactant amounts will decrease and the amount of product will increase
over time.
– As the reactant concentration decreases, the forward reaction rate
slows.
• When a chemical reaction reaches equilibrium, the forward reaction rate is
equal to the reverse reaction rate.
– This does not mean that the amounts of reactants and products are
equal (e.g., 2 reactants = 2 products).
• Reactants products
– Products can react to reform some of the reactants, assuming that the
products are not allowed to escape.
• Processes that proceed in both the forward and reverse directions are said to
be reversible.
– Reactants products
Instructor’s Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach , 3/e, Global Edition © 2016 Pearson Education, Ltd.
Nivaldo J. Tro
Chemical equilibrium and
acids-bases equilibria
5
, Chemical Equilibrium: What Is It All About?
• To ―correct‖ imbalance, a spontaneous flow or transfer from high to low occurs.
• Imbalances can be due to differences in
– concentration,
– pressure,
– energy, or
– temperature.
• Once the imbalance has been rectified, the system is said to be at equilibrium.
• Systems at equilibrium are dynamic in nature and reversible.
– Dynamic: condition in which the forward rate of the reaction is equal to the
reverse rate of the reaction
– Example: A system at equilibrium is one in which the concentrations of
reactants and products remain constant.
• The rates at which the substances are being consumed and made are
the same.
Instructor’s Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach , 3/e, Global Edition © 2016 Pearson Education, Ltd.
Nivaldo J. Tro
, Chemical Equilibrium Does Not Mean Equal
Quantities
• At equilibrium, the forward (kf) and reverse (kr) rates of reactions
are equal.
– kf = kr does not mean that the amounts of reactants and
products are equal.
• Reactions may reach equilibrium only after most of the reactant
molecules have been consumed.
– This indicates that the position of equilibrium favors the
formation of products.
• Reactions may reach equilibrium after only a small percentage of
the reactant molecules has been consumed.
– This indicates that the position of equilibrium favors the
reactants.
Instructor’s Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach , 3/e, Global Edition © 2016 Pearson Education, Ltd.
Nivaldo J. Tro
, Chemical Reaction Dynamics
• At the very beginning of a chemical reaction, the forward reaction rate is
favored:
– Reactants → product formation dominates.
• The reactant amounts will decrease and the amount of product will increase
over time.
– As the reactant concentration decreases, the forward reaction rate
slows.
• When a chemical reaction reaches equilibrium, the forward reaction rate is
equal to the reverse reaction rate.
– This does not mean that the amounts of reactants and products are
equal (e.g., 2 reactants = 2 products).
• Reactants products
– Products can react to reform some of the reactants, assuming that the
products are not allowed to escape.
• Processes that proceed in both the forward and reverse directions are said to
be reversible.
– Reactants products
Instructor’s Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach , 3/e, Global Edition © 2016 Pearson Education, Ltd.
Nivaldo J. Tro
