7.2 The Position of Equilibrium Deduce Kc Le Chatelier’s Principle
Key Points thus far…• A reaction is at equilibrium if :- The rate of the forward reaction = the rate of the backward reaction, therefore quantities remain constant Macroscopically there is no change however microscopically there is constant change Equilibria only exist in a CLOSED SYSTEM – from which no energy exchange is possible An equilibrium can favour products ( rhs ) or reactants (lhs)
Kc and the Magnitude of Kc• Kc is the equilibrium constant, where….• When Kc>> 1, the reaction goes almost to completion.• When Kc<< 1, the reaction hardly proceeds.
Some Examples• For the synthesis of an ester…….
Position of Equilibirum• Consider Ammonia synthesis …..• What will be the effect of removing Ammonia ?• What will be the effect of adding Hydrogen ?
Le Chatelier’s Principle• If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.• If you remove something ( same as decreasing concentration ) the equilibrium will seek to replace it.
Good old Ammonia • Impact of removing – 1. Ammonia – 2. Hydrogen – 3. Nitrogen• Impact of increasing pressure ( GASES ONLY ) – As pressure is a consequence of the impact of gas molecules on its container, the equilibrium will shift to the side with LESS GAS MOLECULES to counteract the change.
So What About Temperature ?• This is a little more complicated.• If exothermic• If endothermic
Is that everything ?• Well……..NO !• Catalysts • A catalyst has absolutely no effect on the position of equilibrium, it merely increases the rate at which equilibrium is reached.