7.1.3—Le Chatelier’s principle to deduce (from

A change in concentration, pressure or temperature disturbs an equilibrium. The system responds in the direction that reduces the effect of that change.

Write the balanced equation first. For gases, compare total gas moles; for temperature, treat heat as a reactant in an endothermic direction or a product in an exothermic direction.

For 2SO₂ + O₂ ⇌ 2SO₃, adding oxygen shifts right and increasing pressure shifts right because three gas moles become two.

The equilibrium shift is not a complete cancellation and a catalyst does not change the final composition. It only speeds both directions.