The Position of Equilibrium

Introduction

• The position of equilibrium in a chemical reaction refers to the extent to which the reaction has occurred.
• It indicates whether the equilibrium favours the formation of products or the persistence of reactants.

Determining Equilibrium Position

• Equilibrium positions can be represented quantitatively as percentages or qualitatively using arrow sizes.

Quantitative Representation

• Equilibrium can be quantitatively represented as the percentage of reactants converted into products.
• For example, if 80% of reactant A is converted into product B, it indicates that the equilibrium lies well on the right-hand side of the reaction.
• The percentage conversion can also be indicated by arrow sizes, with a larger arrow favouring the forward reaction.

Example: Ester Formation

• In ester formation, such as the reaction between ethanoic acid and methanol to produce methyl ethanoate and water, the equilibrium position can be determined.
• If the reaction favours the production of products more than reactants, it is represented as follows:
  • CH3COOH(l) + CH3OH(l) ⇌ CH3COOCH3(l) + H2O(l)
  • A (20%) B (80%)

Qualitative Representation

• Qualitatively, the equilibrium position can be indicated by the direction of the reaction arrow.
• An equilibrium position favouring the forward reaction is shown with a bigger arrow, while an equilibrium position favouring the reverse reaction has a smaller arrow.

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The Position of Equilibrium

Example: Water Dissociation

• In the dissociation of water, where water molecules split into ions, the equilibrium position can be determined.
• If the equilibrium lies to the left, indicating that only a few molecules have split to form ions, it is represented as follows:
  • H2O(l) ⇌ H⁺(aq) + OH⁻(aq)

Constant Equilibrium Position

• Regardless of whether a reaction starts with 100% reactants or 100% products, it will always reach the same equilibrium position.
• Equilibrium is a dynamic state where the forward and reverse reactions occur at the same rate, maintaining a consistent position of equilibrium.