Alevel Chemistry Revision PC 07
Revision Material
Duration: 2nd – 8th March
Topic 7 Equilirbia
This topic illustrates that many chemical reactions are reversible and involve an equilibrium process. The consideration of the many factors that can affect an
equilibrium is an important aspect of physical chemistry.
Learning outcomes
Candidates should be able to:
7.1 Chemical equilibria: (a) explain, in terms of rates of the forward and reverse reactions, what is meant by a reversible
reversible reactions, reaction and dynamic equilibrium
dynamic equilibrium (b) state Le Chatelier’s principle and apply it to deduce qualitatively (from appropriate
information) the effects of changes in temperature, concentration or pressure on a system at
equilibrium
(c) state whether changes in temperature, concentration or pressure or the presence of a
catalyst affect the value of the equilibrium constant for a reaction
(d) deduce expressions for equilibrium constants in terms of concentrations, Kc , and partial
pressures, Kp (treatment of the relationship between Kp and Kc is not required)
(e) calculate the values of equilibrium constants in terms of concentrations or partial pressures
from appropriate data
(f) calculate the quantities present at equilibrium, given appropriate data (such calculations will
not require the solving of quadratic equations)
(g) describe and explain the conditions used in the Haber process and the Contact process, as
examples of the importance of an understanding of chemical equilibrium in the chemical
industry
7.2 Ionic equation (a) show understanding of, and use, the Brønsted-Lowry theory of acids and bases, including the
use of the conjugate acid, conjugate base (acid-I base-I, acid-II base-II) concept
(b) explain qualitatively the differences in behaviour between strong and weak acids and bases
and the pH values of their aqueous solutions in terms of the extent of dissociation
, 7.1 Chemical equilibria: reversible reactions, dynamic equilibrium
(a) Reversible reaction is a reaction in which products can be changed back to reactants by reversing the conditions
Dynamic equilibrium forward and backward reactions occurring at same rate OR the rate of forward and backward
reactions are equal / is the amount of substances in a reversible reaction are unchanged although the reaction is still
occurring. Rate of forward and backward reaction is equal. The concentrations of reactants and products remain constant
(b) state Le Chatelier’s principle and apply it to deduce qualitatively (from appropriate information) the effects of changes in
temperature, concentration or pressure on a system at equilibrium
Le Chatelier’s principle : If the conditions of a system in equilibrium are changed, the position of equilibrium moves so as
to reduce that change
Temperature - Particles move faster at a high temperature, so that the collision frequency
all the reactions will be increase.
faster as temperature rise - The average Ek of particles increases by increasing the temperature, so that
there will be more particles having higher energy than Ea.
- Increasing the number of successful collision per unit time
Concentration of - Increasing number of particles in per unit time, wo that there will be more
reactants chances of collision
Increasing the - The number of particles with higher energy than Ea in per unit volume as
concentration of reactants increasing.
speeds up the reaction. - Increasing the number of successful collision per unit time.
Catalyst - Used to speed up the reaction without chemically change.
with low the Ea for forward - Lower the Ea, so that more particles will have more energy than Ea.
and backward reaction. - The chances of collisions increase.
Surface area - increasing surface area leads to more chances of a collision
Types of catalyst
Heterogeneous in different state provides an alternative reaction pathway lower activation energy
Example
1. Contact Process
Condition 1 400 – 600 ℃
Condition 2 1-10 atm/just above the atmosphere pressure
Condition 3 Vanadium pentoxide/vanadium (V) oxide / V2O5
2. Haber Process
Condition 1 400 – 500 ℃
Condition 2 200 atm
Condition 3 Fe as an catalyst
Revision Material
Duration: 2nd – 8th March
Topic 7 Equilirbia
This topic illustrates that many chemical reactions are reversible and involve an equilibrium process. The consideration of the many factors that can affect an
equilibrium is an important aspect of physical chemistry.
Learning outcomes
Candidates should be able to:
7.1 Chemical equilibria: (a) explain, in terms of rates of the forward and reverse reactions, what is meant by a reversible
reversible reactions, reaction and dynamic equilibrium
dynamic equilibrium (b) state Le Chatelier’s principle and apply it to deduce qualitatively (from appropriate
information) the effects of changes in temperature, concentration or pressure on a system at
equilibrium
(c) state whether changes in temperature, concentration or pressure or the presence of a
catalyst affect the value of the equilibrium constant for a reaction
(d) deduce expressions for equilibrium constants in terms of concentrations, Kc , and partial
pressures, Kp (treatment of the relationship between Kp and Kc is not required)
(e) calculate the values of equilibrium constants in terms of concentrations or partial pressures
from appropriate data
(f) calculate the quantities present at equilibrium, given appropriate data (such calculations will
not require the solving of quadratic equations)
(g) describe and explain the conditions used in the Haber process and the Contact process, as
examples of the importance of an understanding of chemical equilibrium in the chemical
industry
7.2 Ionic equation (a) show understanding of, and use, the Brønsted-Lowry theory of acids and bases, including the
use of the conjugate acid, conjugate base (acid-I base-I, acid-II base-II) concept
(b) explain qualitatively the differences in behaviour between strong and weak acids and bases
and the pH values of their aqueous solutions in terms of the extent of dissociation
, 7.1 Chemical equilibria: reversible reactions, dynamic equilibrium
(a) Reversible reaction is a reaction in which products can be changed back to reactants by reversing the conditions
Dynamic equilibrium forward and backward reactions occurring at same rate OR the rate of forward and backward
reactions are equal / is the amount of substances in a reversible reaction are unchanged although the reaction is still
occurring. Rate of forward and backward reaction is equal. The concentrations of reactants and products remain constant
(b) state Le Chatelier’s principle and apply it to deduce qualitatively (from appropriate information) the effects of changes in
temperature, concentration or pressure on a system at equilibrium
Le Chatelier’s principle : If the conditions of a system in equilibrium are changed, the position of equilibrium moves so as
to reduce that change
Temperature - Particles move faster at a high temperature, so that the collision frequency
all the reactions will be increase.
faster as temperature rise - The average Ek of particles increases by increasing the temperature, so that
there will be more particles having higher energy than Ea.
- Increasing the number of successful collision per unit time
Concentration of - Increasing number of particles in per unit time, wo that there will be more
reactants chances of collision
Increasing the - The number of particles with higher energy than Ea in per unit volume as
concentration of reactants increasing.
speeds up the reaction. - Increasing the number of successful collision per unit time.
Catalyst - Used to speed up the reaction without chemically change.
with low the Ea for forward - Lower the Ea, so that more particles will have more energy than Ea.
and backward reaction. - The chances of collisions increase.
Surface area - increasing surface area leads to more chances of a collision
Types of catalyst
Heterogeneous in different state provides an alternative reaction pathway lower activation energy
Example
1. Contact Process
Condition 1 400 – 600 ℃
Condition 2 1-10 atm/just above the atmosphere pressure
Condition 3 Vanadium pentoxide/vanadium (V) oxide / V2O5
2. Haber Process
Condition 1 400 – 500 ℃
Condition 2 200 atm
Condition 3 Fe as an catalyst
