Le Chatelier's Principle: Effect of Temperature
By Abhishek Sengar | CHEMCA India
Temperature is the only factor that actually changes the numerical value of the Equilibrium Constant (Kc). To understand how heat shifts a reaction, we must treat "Heat" exactly like a chemical reactant or product.
1. Exothermic vs. Endothermic
- Exothermic (ΔH < 0): The reaction releases heat. Treat Heat as a Product.
(Reactants ⇌ Products + Heat) - Endothermic (ΔH > 0): The reaction absorbs heat. Treat Heat as a Reactant.
(Reactants + Heat ⇌ Products)
The Temperature Rule:
- If you Increase Temperature, the system shifts to consume the heat (Shifts in the Endothermic direction).
- If you Decrease Temperature, the system shifts to produce heat (Shifts in the Exothermic direction).
- If you Increase Temperature, the system shifts to consume the heat (Shifts in the Endothermic direction).
- If you Decrease Temperature, the system shifts to produce heat (Shifts in the Exothermic direction).
Practice Question
Q: The dissolution of sugar in water absorbs heat (it gets colder). If you want to dissolve a massive amount of sugar, should you use hot water or cold water?
Answer: Hot Water! Because dissolution is Endothermic (ΔH > 0), increasing the temperature forces the equilibrium to shift forward, dissolving more sugar.
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