Increasing temperature favours the endothermic direction in the stated equilibrium model. Cooling favours the exothermic direction. Start by identifying which direction is endothermic.
A forward exothermic reaction shifts towards reactants when heated. A forward endothermic reaction shifts towards products when heated. Reverse those predictions for cooling.
Reaction speed and equilibrium composition are different outcomes. Heating can make an exothermic forward reaction faster while reducing its equilibrium product fraction.
Predict the direction of change for the reaction and conditions given. You do not need to calculate a percentage yield. All substances stay gaseous in these examples.
Worked example
N₂ + 3H₂ ⇌ 2NH₃ is exothermic forwards. Heating favours the reverse direction and reduces the equilibrium ammonia fraction.
N₂O₄ ⇌ 2NO₂ is endothermic forwards. Heating favours the right-hand side.
Specification references
Higher only: AQA 4.6.2.4 and 4.6.2.6; Edexcel 4.17a. Given energy direction and phase conditions control the prediction.
Copy these details if you'd like to report a problem. Your answers and history aren't included. Nothing is sent automatically.
Write an explanation
Explain why heating an exothermic synthesis can increase reaction speed while reducing equilibrium product fraction.
Compare your explanation with the points below. The text you type isn't marked, saved or sent anywhere.
Compare with the example
Check your explanation for
Separate rate from composition.
Identify the endothermic reverse direction.
State the changed equilibrium prediction.
Example answer
Heating can increase reaction rates, but the new equilibrium favours the endothermic reverse direction. The product fraction can therefore fall even though equilibrium is approached faster.
An answer to improve
A faster reaction must always produce a larger equilibrium yield.
Improve your answer
Name the system, direction and controlled conditions. Replace the unsupported claim with the causal link or evidence that is missing.
Save your progress
Your progress stays in this browser. Turn on saving if you want to keep it when you leave the page.