Effect of Concentration, Pressure and Temperature — Core Principles
Core Principles
Le Chatelier's Principle is a fundamental concept in chemical equilibrium, stating that a system at equilibrium will counteract any applied stress to re-establish a new equilibrium. Three primary stresses are concentration, pressure, and temperature.
Increasing reactant concentration or decreasing product concentration shifts equilibrium towards products. Conversely, decreasing reactant concentration or increasing product concentration shifts it towards reactants.
For gaseous reactions, increasing pressure shifts equilibrium towards the side with fewer moles of gas, while decreasing pressure shifts it towards the side with more moles of gas. Temperature changes affect the equilibrium constant (K) itself.
For exothermic reactions, increasing temperature shifts equilibrium to reactants (decreasing K), while for endothermic reactions, increasing temperature shifts it to products (increasing K). Catalysts accelerate the attainment of equilibrium but do not alter its position.
Often confused with
Side-by-side differences the NEET paper likes to test.
| Aspect | Effect of Concentration, Pressure and Temperature | Effect of Catalyst |
|---|---|---|
| Equilibrium Position | Concentration/Pressure/Temperature | Catalyst |
| Effect on K | Only Temperature changes K; Concentration/Pressure do not | No effect on K |
| Mechanism of Action | Shifts reaction to consume/produce species or heat, or to reduce/increase gas moles | Lowers activation energy for both forward and reverse reactions equally |
| Time to reach Equilibrium | May change, but not directly its primary effect | Decreases time to reach equilibrium |
| Le Chatelier's Principle | Directly explained by Le Chatelier's Principle | Not directly explained by Le Chatelier's Principle as it doesn't relieve a 'stress' by shifting equilibrium |
While concentration, pressure, and temperature changes directly influence the equilibrium position and, in the case of temperature, the equilibrium constant (K), a catalyst only affects the rate at which equilibrium is attained.
A catalyst speeds up both the forward and reverse reactions equally by lowering the activation energy, thereby reducing the time required to reach equilibrium, but it does not alter the final equilibrium concentrations or the value of K.
This distinction is crucial for NEET aspirants.
Why it is tested: NEET relevance: Understanding the distinct role of a catalyst versus other factors is a frequent conceptual question in NEET. Students often confuse catalysts with factors that shift equilibrium, leading to common errors.