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NSWChemistryQuick questions
Module 5: Equilibrium and Acid Reactions
Quick questions on Le Chatelier's principle explained: HSC Chemistry Module 5
13short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is le Chatelier's principle?Show answer
If a system at equilibrium is disturbed by a change in conditions, the system shifts in the direction that partially opposes the disturbance.
What is concentration changes?Show answer
Adding a reactant (or removing a product) shifts the equilibrium to the right (toward products), because the system responds to "use up" the extra reactant.
What is pressure changes (gas reactions)?Show answer
Increasing pressure (by decreasing volume) shifts the equilibrium toward the side with fewer moles of gas.
What is temperature changes?Show answer
This is the only disturbance that changes Kc.
What is catalysts?Show answer
A catalyst increases the rate of both forward and reverse reactions equally. It does not shift the equilibrium position and does not change Kc. It only reduces the time taken to reach equilibrium.
What is pressure: 200 atm?Show answer
Forward reaction goes from 4 moles of gas to 2. High pressure shifts equilibrium right (toward ammonia), increasing yield. Pressure is limited by reactor cost.
What is temperature: 400°C?Show answer
Forward reaction is exothermic. Le Chatelier favours low temperature for yield. But low temperature reduces the rate.
What is iron catalyst?Show answer
Speeds up the approach to equilibrium without changing position.
What is continuous removal of ammonia?Show answer
$NH_3$ is liquefied and removed. Le Chatelier predicts the system shifts further right to replace the removed product.
What is confusing rate and position?Show answer
A catalyst changes the rate, not the position. Temperature changes both.
What is forgetting that Kc only changes with temperature?Show answer
Concentration and pressure shifts change the position but not the constant.
What is mixing up endothermic and exothermic?Show answer
If the forward reaction is exothermic, heat is a product. Adding heat (raising T) shifts equilibrium left. Treat heat as a chemical species when in doubt.
What is adding inert gas at constant pressure?Show answer
This expands the volume and decreases partial pressures, so the equilibrium does shift. At constant volume, it does not. Read the question carefully.