Short Answer

Temperature affects equilibrium by shifting the balance between the forward and backward reactions. If the temperature is increased, the equilibrium shifts in the direction that absorbs heat (endothermic direction). If the temperature is decreased, the equilibrium shifts in the direction that releases heat (exothermic direction).

This behaviour follows Le Chatelier’s principle, which states that when a change is applied to a system at equilibrium, the system adjusts itself to reduce the effect of that change. Temperature also affects the value of the equilibrium constant (K), making it an important factor in controlling chemical reactions.

Detailed Explanation :

Effect of Temperature on Equilibrium

Temperature plays a very important role in determining the position and behaviour of equilibrium in a reversible reaction. Every chemical reaction involves heat — either released (exothermic) or absorbed (endothermic). When temperature changes, the system must adjust to this disturbance by shifting the equilibrium position to oppose the change. This is explained by Le Chatelier’s principle.

Understanding how temperature affects equilibrium helps chemists predict product yield, control industrial reactions, and understand many natural processes. Temperature not only shifts the equilibrium position but also changes the equilibrium constant (K), making it one of the most powerful factors influencing equilibrium.

1. Role of Heat in Chemical Reactions

Before understanding how temperature affects equilibrium, it is important to know that:

1. a) Exothermic Reactions Release Heat

Heat is treated as a product.
For example:
A + B ⇌ C + heat

1. b) Endothermic Reactions Absorb Heat

Heat is treated as a reactant.
For example:
A + heat ⇌ B + C

This idea helps explain why equilibrium shifts when temperature changes.

2. Effect of Increasing Temperature

When temperature is increased, extra heat is added to the system.

According to Le Chatelier’s principle:

• The system will shift toward the side that absorbs heat to reduce the temperature increase.
• Therefore, equilibrium shifts in the endothermic direction.

If forward reaction is endothermic

• More products are formed
• Equilibrium shifts to the right

If forward reaction is exothermic

• More reactants are formed
• Equilibrium shifts to the left

Effect on Equilibrium Constant (K)

For endothermic reactions: K increases with temperature.
For exothermic reactions: K decreases with temperature.

3. Effect of Decreasing Temperature

When temperature is decreased, heat is removed from the system.

According to Le Chatelier’s principle:

• The system shifts to the side that releases heat to replace the lost heat.
• Therefore, equilibrium shifts in the exothermic direction.

If forward reaction is exothermic

• More products form
• Equilibrium shifts to the right

If forward reaction is endothermic

• More reactants form
• Equilibrium shifts to the left

Effect on Equilibrium Constant (K)

For endothermic reactions: K decreases when temperature decreases.
For exothermic reactions: K increases when temperature decreases.

4. Why Temperature Change Alters Equilibrium Constant

Unlike concentration or pressure changes, temperature directly affects the energy of particles and the energy barrier of reactions.
Because of this:

• Temperature changes reaction rates differently for forward and backward reactions.
• As a result, the ratio of product to reactant concentrations (K) changes.

This makes temperature the only factor that changes the value of K.

5. Practical Applications of Temperature Effect on Equilibrium
6. a) Haber Process (Ammonia Production)

N₂ + 3H₂ ⇌ 2NH₃ + heat
This is an exothermic reaction.
To increase product yield:

• Lower temperature is favoured
• But very low temperature slows reaction
• So a moderate temperature is used (around 450°C)

1. b) Contact Process (Sulphuric Acid Production)

Reaction forming SO₃ is exothermic.
Lower temperature gives higher yield but slower speed.
A compromise temperature is used in industries.

1. c) Biological Systems

Enzyme-controlled equilibria in the body are sensitive to temperature, which is why body temperature must remain stable.

6. Summary of Temperature Effect

• Increase in temperature → favour endothermic direction
• Decrease in temperature → favour exothermic direction
• Temperature affects K, unlike pressure or concentration
• Equilibrium shifts to counteract temperature change
• Industrial processes use temperature control to maximise product formation

Conclusion

Temperature has a strong effect on chemical equilibrium by shifting the balance between forward and backward reactions. Increasing temperature favours the endothermic direction, while decreasing temperature favours the exothermic direction. This adjustment helps the system minimize the impact of temperature changes, following Le Chatelier’s principle. Temperature also changes the equilibrium constant (K), making it a crucial factor in controlling product yield in industrial processes and understanding natural chemical systems.