6.3.3 — Temperature Shifts & Equilibrium Yield
Le Chatelier's Principle · 15 Questions · 50 Marks Total
⚡ The One Rule To Rule Them All
↑ Temperature → Equilibrium shifts in the ENDOTHERMIC direction
↓ Temperature → Equilibrium shifts in the EXOTHERMIC direction
Section A
5 Qs
Section B
5 Qs
Section C
5 Qs
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📐 Section A — The Golden Rules
Conceptual understanding of Le Chatelier's Principle & Temperature
Le Chatelier's Principle states: 'If a system at equilibrium is subjected to a change, the system will respond to oppose that change.' When temperature is increased, in which direction does the equilibrium shift?
[2 marks]When temperature is decreased, in which direction does the equilibrium shift?
[2 marks]For a reversible reaction where the forward reaction is exothermic (ΔH = −ve), state the effect of increasing temperature on: (a) the position of equilibrium and (b) the yield of products.
[4 marks]For a reversible reaction where the forward reaction is endothermic (ΔH = +ve), state the effect of decreasing temperature on: (a) the position of equilibrium and (b) the yield of products.
[4 marks]A student says: 'Changing temperature does not affect the equilibrium constant K.' Is this student correct? Explain.
[3 marks]🔥 Section B — Exothermic Forward Reaction
ΔH = −ve · Predicting shifts when temperature changes
Consider the equilibrium: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = −92 kJ/mol What is the effect of DECREASING temperature on the yield of ammonia (NH₃)?
[3 marks]Consider the equilibrium: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = −196 kJ/mol A factory increases the reaction temperature from 400°C to 600°C to speed up production. Predict the effect on the yield of SO₃.
[3 marks]Consider the equilibrium: CO(g) + 3H₂(g) ⇌ CH₄(g) + H₂O(g) ΔH = −206 kJ/mol State and explain the effect of increasing temperature on the position of equilibrium.
[4 marks]Consider the equilibrium: Fe₃O₄(s) + 4H₂(g) ⇌ 3Fe(s) + 4H₂O(g) ΔH = −150 kJ/mol A student wants to maximise the yield of iron (Fe). Should they use a HIGH or LOW temperature? Justify your answer.
[3 marks]Consider the equilibrium: H₂(g) + I₂(g) ⇌ 2HI(g) ΔH = −10 kJ/mol At 700 K the yield of HI is 78%. Predict whether the yield at 300 K would be higher or lower than 78%. Explain.
[3 marks]🧊 Section C — Endothermic Forward Reaction
ΔH = +ve · Predicting shifts when temperature changes
Consider the equilibrium: N₂(g) + O₂(g) ⇌ 2NO(g) ΔH = +180 kJ/mol What is the effect of INCREASING temperature on the yield of NO?
[3 marks]Consider the equilibrium: CaCO₃(s) ⇌ CaO(s) + CO₂(g) ΔH = +178 kJ/mol Explain why this reaction is carried out at high temperatures in industry.
[4 marks]Consider the equilibrium: CH₄(g) + H₂O(g) ⇌ CO(g) + 3H₂(g) ΔH = +206 kJ/mol A student decreases the temperature. Predict the effect on: (a) the position of equilibrium and (b) the yield of H₂.
[4 marks]Consider the equilibrium: Fe²⁺(aq) + Co(NH₃)₆²⁺(aq) ⇌ Fe³⁺(aq) + Complex(aq) ΔH = +45 kJ/mol Describe and explain what happens to the colour intensity of Fe³⁺ when temperature is increased.
[3 marks]The decomposition of N₂O₄ into NO₂ is endothermic: N₂O₄(g) ⇌ 2NO₂(g) ΔH = +57 kJ/mol N₂O₄ is colourless; NO₂ is brown. A sealed tube of the equilibrium mixture is placed in hot water. Describe and fully explain the observed colour change.
[5 marks]🔑 Master Reference Card
🔥 Exo Forward (ΔH = −ve)
↑ Temp → ↓ Yield
↓ Temp → ↑ Yield
🧊 Endo Forward (ΔH = +ve)
↑ Temp → ↑ Yield
↓ Temp → ↓ Yield
📌 The K Rule
Temperature is the ONLY factor that changes the value of the equilibrium constant K. Concentration and pressure changes shift the position of equilibrium but leave K unchanged.
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