Describe the effect on the equilibrium position of increasing the temperature of a reversible reaction in which the forward reaction is exothermic.

Cambridge International IGCSE Chemistry (0620) — 6.3 Reversible reactions and equilibrium · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Many industrial processes involve reversible reactions. In one such reaction, the forward reaction releases energy to the surroundings.

Model answer (4 marks)

The equilibrium shifts toward the reactants.

The added heat is absorbed by the endothermic reverse reaction.

Consequently the concentration of products falls.

The concentration of reactants rises at equilibrium.

Examiner tips

Use the word "shifts" to show direction; mention heat as a reactant for the reverse step; link temperature change to product/reactant concentrations; keep answer concise and use correct terminology.
Remember the exothermic forward reaction loses heat, so adding heat favours the reverse (endothermic) direction.

Common mistakes

Saying the equilibrium shifts toward the products; confusing exothermic with endothermic direction.
Using vague terms like "more of something" without specifying reactants or products.

Mark scheme (4 marks)

The equilibrium position shifts in the reverse/backward direction
Because the reverse reaction is endothermic / the system absorbs the extra heat energy
The yield / proportion / concentration of products decreases
The concentration of reactants increases / more reactants are present at equilibrium

Key terms in this question

equilibrium position · reversible reaction · exothermic