Chemistry AQA AS Unit 2 Equilibria

Made these notes for my year 12 summer exam to revise and read over. There are spelling mistakes in most of my files but due to the busy exam schedule I had no time to correct them (sorry).

Most files have more information than what is needed but I feel it helps you feel more confident walking into the exam if you have a greater knowledge background and may help when having to apply knowledge to questions. Good luck :)

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  • Created by: Chelcie
  • Created on: 02-09-13 13:31
Preview of Chemistry AQA AS Unit 2 Equilibria

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Equilibria
EQUILIBRIUM MIXTURE: Where the forward and backwards reactions are still occurring but at the
same rate in a closed system.
DYNAMIC EQUILIBRIUM:
1) Concentration of reactants and products is CONSTANT
2) Rate of the forward and reverse reactions is the same
Initially the rate in the forward direction is fast.
As products are made, the reverse reaction
begins slowly at first.
When equilibrium is reached, the rates are the
same.
Equilibrium can only be reached in a closed system.
Known equilibrium has been reached when the macroscopic properties (properties that do not
depend on the total quantity of matter) of the system do not change e.g. pressure/colour/density.
Changing the position of the Equilibrium
Le Châtelier's:
"If any factor is changed which affects the equilibrium, the position of the equilibrium shifts to
oppose that change."
Position of equilibrium Yield
In the middle 50%
To the left 10%
To the right 90%
Changing temperature
(exothermic) A + B C + D (endothermic)
Increasing the temperature will shift the position of the equilibrium to the right hand
side to oppose the change, because this equation is in the endothermic direction.
(It is already boiling to the left so has to regain balance and move to the right)
Changing pressure of gases
A (g) + 3B (g) C (g) + D (g)
Increasing the pressure will shift the position of the equilibrium to the right to oppose the change as
there are fewer molecules of gas on the right.
If there are equal molecules on both sides, pressure will have no effect.

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Changing concentration
F (aq) + G (aq) H (aq) + I (aq)
Increasing [G (aq)] will shift equilibrium to the right to oppose the effect. F will decrease
as being used up.
Increasing [H (aq)] will shift equilibrium to the left to oppose the effect. I will decrease as being used
up.
Decreasing [I (aq)] will shift equilibrium to the right. F + G will decrease and H will increase.…read more

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