1
CHEM1048A
Chemistry I
Chemical Equilibrium
Acknowledgement of material:
Brown et al, Chemistry: The Central
Lecturer: Dr M. Maphupha
Science, Global Edition, 15thEdition. Office: C505, Humphrey Raikes Building
Staff from the Wits School of Email:
Chemistry
,2
The Concept of Equilibrium
➢ Chemical equilibrium occurs when the rate of the forward
reaction equals the rate of the reverse reaction.
➢ This can be achieved only when a chemical reaction is
reversible in a closed system.
➢ Consider the dissociation of N2O4 to form NO2
N2O4 (g) 2NO2 (g)
➢ At equilibrium, an equilibrium mixture of N2O4 and NO2
remains, wherein the concentrations of the gases no longer
change with time.
,3
The Concept of Equilibrium
➢ Equilibrium is reached in the third picture.
➢ Dynamic equilibrium is shown by writing the reaction equation with two half-
arrows pointing in opposite directions:
© 2018 Pearson Education, Inc.
, 4
The Equilibrium Constant
For the dissociation of N2O4 to NO2
Forward reaction:
N2O4 (g) → 2 NO2 (g)
Rate Law:
Ratef = kf [N2O4]
© 2018 Pearson Education, Inc.
CHEM1048A
Chemistry I
Chemical Equilibrium
Acknowledgement of material:
Brown et al, Chemistry: The Central
Lecturer: Dr M. Maphupha
Science, Global Edition, 15thEdition. Office: C505, Humphrey Raikes Building
Staff from the Wits School of Email:
Chemistry
,2
The Concept of Equilibrium
➢ Chemical equilibrium occurs when the rate of the forward
reaction equals the rate of the reverse reaction.
➢ This can be achieved only when a chemical reaction is
reversible in a closed system.
➢ Consider the dissociation of N2O4 to form NO2
N2O4 (g) 2NO2 (g)
➢ At equilibrium, an equilibrium mixture of N2O4 and NO2
remains, wherein the concentrations of the gases no longer
change with time.
,3
The Concept of Equilibrium
➢ Equilibrium is reached in the third picture.
➢ Dynamic equilibrium is shown by writing the reaction equation with two half-
arrows pointing in opposite directions:
© 2018 Pearson Education, Inc.
, 4
The Equilibrium Constant
For the dissociation of N2O4 to NO2
Forward reaction:
N2O4 (g) → 2 NO2 (g)
Rate Law:
Ratef = kf [N2O4]
© 2018 Pearson Education, Inc.
