9. Equilibria Flashcards
What happens if we put a reversible reaction in a closed system?
As soon as the products are formed they react together and form the reactants again so instead of reactants OR products, we get a mixture of both.
Give an example of a reversible reaction.
CuSO4.5H2O CuSO4 + 5H2O
Blue hydrated white anhydrous
Copper sulfate copper sulfate
What happens eventually in a reversible reaction in a closed system?
Eventually we get a mixture in which the proportions of all three components remain constant. The mixture is called an equilibrium mixture.
Define dynamic equilibrium
A situation in which the composition of a reaction mixture does not change because both forward and backward reactions are proceeding at the same rate.
What are four conditions which apply to all equilibria?
- equilibrium can only be reached in a closed system (one where the reactants and products can’t escape - doesn’t have to be ‘sealed’.
- equilibrium can be approached from with direction and the final equilibrium position will be the same.
- equilibrium is a dynamic process. It is reached when the rates if two opposing processes are the same.
- we know that equilibrium have been reached when the macroscopic properties of the system do not change with time. E.g density, concentration, colour and pressure
Describe the stages of reacting equilibrium…
At the start of the reaction the forward rate is fast because A and B are plentiful, there is no reverse reaction.
Then as the concentrations of C and D build up the reverse reaction speeds up. At the same time the concentrations of A and B decrease so the forward reaction slows down.
We reach a point where exactly the same number of particles are changeling from A + B to C + D and visa versa.
Which chemical processes have reversible reactions as a key step?
The production of ammonia and the production of sulfuric acid.
Give Le Chaterlier’s principle
If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to oppose the change.
What can we not predict using Le Chatelier’s principle?
The quantities involved in a reaction.
Which reactions do pressure changes affect?
Pressure changes only affect reactions involving gases.
If more pressure is put on a reversible reaction (with gases) what will happen?
The reaction will shift to the side of the reaction which has less moles of substance.
What happens when you increase the temperature of a reversible reaction?
The reaction will favour the direction which is endothermic (absorbs heat)
What effect do catalysts have on reversible reactions?
Catalysts have no effect on the position of equilibrium so they do not alter the composition of the equilibrium mixture. Catalysts speed up reactions and this affects the forward and back reactions equally.
However, they do allow equilibrium to be reached more quickly - vital in industry.
What is used to make fertilisers and synthetic fibres, dyes and plastics?
Ammonia (NH3)
Give the reaction for the production of ammonia.
N2 (g) + 3H2 2NH3
