BRAINCAKELimitations of Predictions
Le Chatelier's principle is a useful rule, but its predictions have limitations.
1. It is qualitative. It predicts the direction in which the position of equilibrium shifts, but not how far it shifts. To calculate the new equilibrium composition you need the equilibrium constant, Kc.
2. It says nothing about rate. It predicts the equilibrium position, not how quickly equilibrium is reached. A low temperature may favour the products of an exothermic reaction, but the reaction may then be so slow that equilibrium is never reached in a useful time.
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Key terms in this lesson
- le chatelier's principle
- If a system at equilibrium is subjected to a change in conditions, the position of equilibrium shifts to oppose that change.
- equilibrium constant
- A value, Kc, expressing the ratio of product to reactant concentrations at equilibrium for a reaction at a given temperature.
More in Reversible Reactions and Dynamic Equilibrium
- Effect of Change in Concentration
- Effect of Change in Pressure
- Effect of Change in Temperature
- Effect of Catalysts
- Homogeneous and Heterogeneous Equilibria
- The Equilibrium Law
- Homogeneous Systems
- Heterogeneous Systems
All 18 lessons in Reversible Reactions and Dynamic Equilibrium · All Edexcel AS-level Chemistry topics