Give the balance a nudge.
A disturbed equilibrium changes in the direction that partly opposes the disturbance. Adding a reactant usually favours its consumption. Immediately after addition, only that species has a direct concentration jump; the subsequent reaction changes all reacting species.
Compressing a gaseous mixture favours the side with fewer moles of gas, when the two sides differ. For N₂ + 3H₂ ⇌ 2NH₃, compression favours ammonia. Pressure changes caused solely by an inert gas at constant volume do not change the reacting species concentrations.
For an exothermic forward reaction, heating favours the reverse reaction and lowers K. Only temperature changes K for a specified reaction. A catalyst speeds the approach to equilibrium without changing its position or K.
A balance that keeps moving
Illustrative A ⇌ B model in a closed system; total concentration 1.00 mol L⁻¹. Ratio K = [B]/[A]. Not a model of any particular industrial reaction.
Explore: Change one condition and distinguish the immediate disturbance from the new balance.
Explain why heating an exothermic equilibrium reduces product yield.
- The system responds by absorbing added energy.
- The reverse reaction is endothermic, so product is consumed.
Answer: Heating favours the endothermic reverse reaction, shifting equilibrium towards reactants.
Assumed knowledge
Gas coefficients count relative moles. Exothermic reactions release heat.
Learning checkpoints & source
YOUR SYLLABUS CHECKPOINT- Predict changes caused by concentration, pressure and temperature.
- Distinguish a change in equilibrium position from a change in K.