IB CHEMISTRY:
TOPIC 7 EQUILIBRIUM NOTES
7.1 Equilibrium
Dynamic equilibrium
Chemical equilibrium is a state in which the rate of the forward reaction equals the
rate of the backward reaction
In other words the forward and reverse reactions will continue to occur, but the
concentration will stay the same
Such a system is said to be in a state of dynamic equilibrium. Characteristics of
equilibrium include:
Feature of equilibrium state Explanation
1 Equilibrium is dynamic The reaction has stopped but both forward and backward reactions
are still occurring at the same rate
2 Equilibrium is achieved in a closed A closed system prevents exchange of matter with the surroundings,
system so equilibrium is achieved where both reactants and products can
react and recombine.
3 The concentrations of reactants and They are being produced and destroyed at an equal rate.
products remain constant
4 There is no change in macroscopic Color and density do not change as these depend on the
properties concentrations.
5 Equilibrium can be reached from either The reaction can be started with all reactants, all products or a
direction (products or reactants) mixture.
Example: In a closed container, liquid bromine is in a dynamic equilibrium with its vapor.
There will always be both liquid and gas bromine in the flask. This state is described as a
dynamic equilibrium. Vaporization and condensation are both happening simultaneously
in the flask. Liquid bromine is in dynamic equilibrium with bromine vapour. This can be
presented as:
Br2 (l)⇄ Br2 (g)
Dynamic equilibrium can only be established in a closed system where reactants and
products cannot escape
Equilibrium Constant: Kc
An equilibrium reaction can be represented as aA +bB ⇄ cC+ dD
Lower case letters represent the number of moles (coefficient), the uppercase letters
represent the molecule itself
TOPIC 7 EQUILIBRIUM NOTES
7.1 Equilibrium
Dynamic equilibrium
Chemical equilibrium is a state in which the rate of the forward reaction equals the
rate of the backward reaction
In other words the forward and reverse reactions will continue to occur, but the
concentration will stay the same
Such a system is said to be in a state of dynamic equilibrium. Characteristics of
equilibrium include:
Feature of equilibrium state Explanation
1 Equilibrium is dynamic The reaction has stopped but both forward and backward reactions
are still occurring at the same rate
2 Equilibrium is achieved in a closed A closed system prevents exchange of matter with the surroundings,
system so equilibrium is achieved where both reactants and products can
react and recombine.
3 The concentrations of reactants and They are being produced and destroyed at an equal rate.
products remain constant
4 There is no change in macroscopic Color and density do not change as these depend on the
properties concentrations.
5 Equilibrium can be reached from either The reaction can be started with all reactants, all products or a
direction (products or reactants) mixture.
Example: In a closed container, liquid bromine is in a dynamic equilibrium with its vapor.
There will always be both liquid and gas bromine in the flask. This state is described as a
dynamic equilibrium. Vaporization and condensation are both happening simultaneously
in the flask. Liquid bromine is in dynamic equilibrium with bromine vapour. This can be
presented as:
Br2 (l)⇄ Br2 (g)
Dynamic equilibrium can only be established in a closed system where reactants and
products cannot escape
Equilibrium Constant: Kc
An equilibrium reaction can be represented as aA +bB ⇄ cC+ dD
Lower case letters represent the number of moles (coefficient), the uppercase letters
represent the molecule itself
