Factors Affecting Equilibria

6.8 Factors Affecting Equilibria

The central goal in chemical synthesis is to get the maximum possible conversion of reactants into products while using the least energy. That means achieving a high yield under mild conditions of temperature and pressure. When a reaction does not give a satisfactory yield, the experimental conditions must be adjusted. The Haber process for ammonia synthesis — producing roughly a hundred million tonnes of ammonia each year, mostly for fertilisers — is a classic example where the choice of conditions has enormous economic importance.

The equilibrium constant $K_c$ is independent of initial concentrations. But if a system at equilibrium is disturbed — by changing the concentration of a reactant or product, or by altering temperature or pressure — the system is no longer at equilibrium. A net reaction then proceeds in one direction until equilibrium is re-established.

To predict which direction the reaction will shift, we use Le Chatelier's principle.

This principle applies to all physical and chemical equilibria. We now examine each factor that can influence equilibrium.

The Four Factors, Section by Section

Each factor gets its own detailed treatment: concentration changes (§6.8.1), pressure changes (§6.8.2), inert-gas addition (§6.8.3), temperature changes (§6.8.4) and the role of a catalyst (§6.8.5).

Summary Table of Effects