Changing Temperature

Introduction

Altering the temperature of an equilibrium mixture affects the position of equilibrium.
The direction of the shift depends on the enthalpy change (heat) of the reaction.

Increasing temperature favours the endothermic reaction.
In an endothermic reaction, heat is absorbed when the reaction proceeds.
An increase in temperature shifts the equilibrium to the right, favouring the formation of products.
This results in more product formation, causing observable changes.

lightbulbExample

Example: Dinitrogen Tetroxide and Nitrogen Dioxide

Consider the equilibrium between dinitrogen tetroxide and nitrogen dioxide:

N₂O₄(g) ⇌ 2NO₂(g)

The forward reaction is endothermic, so increasing the temperature shifts the equilibrium to the right.

More nitrogen dioxide is formed, and the mixture becomes darker in colour.

Decreasing temperature favours the exothermic reaction.
In an exothermic reaction, heat is released when the reaction proceeds.
A decrease in temperature shifts the equilibrium to the left, favouring the formation of reactants.
This results in more reactant formation, causing observable changes.

lightbulbExample

Example: Haber Process

In the industrial manufacture of ammonia using the Haber process, the equilibrium is:

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

The forward reaction is exothermic, and a moderately high temperature (380 - 450°C) is used.

diagram

If the temperature is increased, the equilibrium shifts to the left (endothermic direction) to remove the extra heat added.
Lowering the temperature favours the exothermic reaction, producing more heat and shifting the equilibrium to the right.

Changing the temperature of a chemical equilibrium can shift the equilibrium position.
The shift depends on whether the reaction is endothermic (absorbs heat) or exothermic (releases heat).
Understanding this concept is crucial in industrial processes like the Haber process for ammonia production.