Equilibrium

Notes

Important Terms

• In dynamic equilibrium, macroscopic properties are constant (concentrations of all reactants and products remains constant) and the rate of the forward reaction is equal to the rate of the reverse reaction.
  
  • Note: Constant concentration does not mean equal concentration

Characteristics of Equilibrium

1. Macroscopic properties are constant at equilibrium – at equilibrium the concentrations of all reactants and products remain constant.
2. At equilibrium the rate of the forward reaction is equal to the rate of the reverse reaction.
3. Equilibrium can be attained only in a closed system.
4. All species in the chemical equation are present in the equilibrium reaction mixture
5. Equilibrium can be attained from either direction

Position of Equilibrium (Le Chatelier’s principle)

• The ‘position of equilibrium’ refers to the relative amounts of reactants and products present at equilibrium.
• Equilibrium does not imply 50% reactants and 50% products.
• If a system at equilibrium is subjected to a change, the position of equilibrium will shift in order to minimize the effect of the change.

Temperature

• As temperature increases, the position of equilibrium shifts in the endothermic direction to take in heat to minimize the effect.

• Heat reaction mixture: position of equilibrium is shifted in the endothermic direction.

• Cool reaction mixture: position of equilibrium is shifted in the exothermic direction.

Pressure

• If a reaction involves a change in the number of gas molecules, an increase in pressure results in the position of equilibrium shifting in the direction that gives a decrease in the number of gas molecules.

Concentration