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Chemical Equilibria

Lajoy Tucker

Teacher

Lajoy Tucker

Contents

Definition

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Features of Dynamic Equilibrium

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Position of Equilibrium

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Definition

Reversible reactions are reactions in which the products can reform the reactants.

The forward reaction describes reactants being converted to products . The reverse reaction describes products being converted back to reactants .

A dynamic equilibrium is established in a closed system when:

  • The forward and reverse reactions occur at the same rate.

  • The concentrations of reactants and products remain constant.

Graph to show the rate of the forward and reverse reactions over time

Graph showing how the rates of the forward and reverse reactions change over time until dynamic equilibrium is reached, where both reaction rates become equal and remain constant.

No answer provided.

Features of Dynamic Equilibrium

  • The macroscopic properties (e.g. concentration, pressure) appear unchanging.

  • Molecular-level processes continue in both directions.

  • No net change in amounts of products/reactants once equilibrium is reached.

Position of Equilibrium

For a system in dynamic equilibrium, there is no net change in the concentrations of reactants and products but this does not mean that the concentrations of reactants and products are equal.

The position of equilibrium indicates which side is favoured:

  • More products → "lies to the right"

  • More reactants → "lies to the left"

Graphs to show the concentrations of reactants and products over time.

Particle diagram representing a reversible reaction at dynamic equilibrium, where reactants and products are continuously converting into each other at equal rates.

Graph and particle diagram showing a reversible reaction where equilibrium lies to the right, with a higher concentration of products than reactants at equilibrium.

Graph and particle diagram showing a reversible reaction where equilibrium lies to the left, with a higher concentration of reactants than products at equilibrium.

Graph and particle diagram showing a reversible reaction where equilibrium lies in the centre, with equal concentrations of reactants and products at equilibrium.

No answer provided.

Question

On the graph below for the reaction between nitrogen and hydrogen,

State the time at which the reaction reaches dynamic equilibrium.

Justify your choice

Concentration–time graph for the Haber process showing nitrogen and hydrogen concentrations decreasing while ammonia concentration increases until dynamic equilibrium is reached.

(Approximately) 40 seconds.

There is no net change in the concentrations of the reactants and products (concentrations remain constant).

Le Chatelier's Principle