Summary The much needed chemical equilibrium extra notes

Chapter 15: Chemical Equilibrium




Dr Grace Ngubeni

, The Concept of Equilibrium
• Chemical equilibrium occurs when opposing reactions
are proceeding at equal rates.
• 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)
Colourless brown

• At equilibrium an equilibrium mixture of N2O4 and NO2
remains, wherein the concentrations of the gases no
longer change with time.

,The Concept of Equilibrium

, The Concept of Equilibrium

• Using Reaction Kinetics, the equation
N2O4 (g)  2 NO2 (g)

• The rate laws for the forward and reverse elementary
reactions can be written as follows:

Forward Reaction: N2O4 (g) → 2 NO2 (g) Rate = k [N O ]
f f 2 4
Reverse Reaction: 2 NO (g) → N O (g) Rate r = k r [NO2 ]2
2 2 4

Rate constants