Chemical equilibria and Le Chatelier's principle Flashcards
In a reversible reaction at equilibria:
Forward and reverse reactions proceed at equal rates
The concentrations of reactants and products remain constant.
Le Chatelier’s principle
Le Chatelier’s principle says that if a change is made to a system in dynamic equilibrium, the position of the equilibrium moves to counteract this change.
What is the principle used for?
The principle is used to predict changes to the position of equilibrium when there are changes in temperature, pressure or concentration in homogeneous reactions
What doesn’t affect the position of equilibria?
A catalyst
A catalyst is a substance that increases the rate of a chemical reaction (they increase the rate of the forward and reverse reaction equally)
Catalysts only cause a reaction to reach equilibrium faster
Catalysts therefore have no effect on the position of the equilibrium once this is reached
The Haber process
N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH= -76kJmol
Ideal conditions of haber process: the issues
Low temp: comprimise as this slows rate of reaction
High pressure: expensive (high energy plus specialist equipment), dangerous
Ideal conditions of haber process
450 degrees C, 20000kPa, iron catalyst, recycle unused reaction
Why cant we add more nitrogen in haber process
Not enough hydrogen would come into contact with catalyst
The contact process
2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH= -196 kJmol
ideal conditions of contact process
low temp (450) high pressure (150kPa) catalyst (V2O5)
