Intermediate Topic 473 of 1102 Kinetics & Equilibrium
Effect of Pressure on Equilibrium
Increasing pressure shifts equilibrium toward the side with fewer gas moles.
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In-depth explanation of Effect of Pressure on Equilibrium
Changing the pressure of a gas-phase equilibrium affects it only when the number of gas molecules differs between reactants and products. Increasing the pressure by reducing the volume shifts the reaction toward the side with fewer moles of gas, because this lowers the total pressure. Reactions in which the number of gas moles is unchanged are not affected by pressure changes. Adding an inert gas at constant volume does not change the partial pressures of the reacting species, so it has no effect on the position of equilibrium. Adding an inert gas at constant pressure does shift the equilibrium toward the side with more moles, because the volume increases.
Going deeper: Effect of Pressure on Equilibrium
Key ideas: Pressure shifts the position only if delta n for gases is nonzero. For N2 + 3H2 <-> 2NH3, doubling pressure through halving volume makes Q = K/4 for the ammonia expression, so the reaction goes forward. Adding an inert gas at constant volume leaves partial pressures unchanged, while at constant pressure it effectively dilutes the system.
Common mistakes and connections: Students apply pressure arguments to liquids and solids, which are nearly incompressible, or think that raising pressure changes K. K stays the same at fixed temperature. Another error is mixing up total pressure with partial pressure when adding inert gas. For delta n = 0 no shift occurs. Industrial results such as the Haber process combine pressure effects with kinetics and cost.
Visualization of Effect of Pressure on Equilibrium
Four moles of gas become two in N2 + 3H2 to 2NH3, so higher pressure raises the equilibrium ammonia content (ideal-gas estimate). The interactive lesson shows this as a live animation or chart.
Worked example and use case
Higher pressure favours ammonia formation from nitrogen and hydrogen, since four moles of gas become two moles.
Frequently asked questions about Effect of Pressure on Equilibrium
What is Effect of Pressure on Equilibrium?
Increasing pressure shifts equilibrium toward the side with fewer gas moles.
Is Effect of Pressure on Equilibrium a beginner, intermediate or advanced topic?
Effect of Pressure on Equilibrium is a intermediate topic in Kinetics & Equilibrium. It builds on the vocabulary of beginner topics in this area.
What should I learn before Effect of Pressure on Equilibrium?
Study these earlier topics in Kinetics & Equilibrium first: ICE Tables, Le Chatelier's Principle, Effect of Concentration on Equilibrium.
What comes after Effect of Pressure on Equilibrium?
The next topics in Kinetics & Equilibrium are Effect of Temperature on Equilibrium and Effect of Catalyst on Equilibrium.
Can I practise Effect of Pressure on Equilibrium with quizzes?
Yes. The interactive lesson includes a self-check question on Effect of Pressure on Equilibrium, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Effect of Pressure on Equilibrium fits in Kinetics & Equilibrium
Effect of Pressure on Equilibrium is topic 54 of 91 in Kinetics & Equilibrium.