How can we use Le Chatelier's Principle to increase yields of chemical reactions?
We adjust the conditions to make the equilibrium favour the products.
Le Châtelier’s Principle states that a change in pressure, temperature, or concentration will push the equilibrium to one side of the chemical equation.
So, if you manipulate the conditions to favour the product side, you increase the yield.
1. Increase the temperature of an endothermic reaction.
An endothermic reaction absorbs energy. If you add energy, you favour the product forming reaction.
2. Decrease the temperature of an exothermic reaction.
An exothermic reaction gives off energy. If you remove the energy, you favour the product forming reaction.
3. Increase the pressure for a gaseous system in which the product side has fewer moles.
The reaction goes towards the products.
4. Increase the concentration of a reactant in an aqueous solution.
The reaction goes to the side of products.
Consider the reaction
N₂(g) + 3H₂(g) ⇌ 2NH₃(g); ΔH = -92.4 kJ
We would use a high pressure because there are fewer moles of gas on the right.
We would use a low temperature because the reaction is exothermic.