Equilibria

Page 1

Equilibria

CuSO4.5H2O == CuSO5 +5H2O

Equilibrium is not a 50/50 split (BOB AND Maud model)

More products - move to the right

More reactions - move to the left

Dynamic equilibrium

-Is only in a closed system

-It can be reached from either direction

-Equilibrium is when the rate of forwards reaction equals the rate of the backwards reaction

-Equilibrium is dynamic because even though the macroscopic properties remain constant i.e concentration of reactants and products - the actual molecules change

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Le Chatelier's principle

- If a system in equilibrium is changed, the position of the equilibrium will move to reduce the change

Change in concentration:

A+B == C+D

Add C - move to left to remove C

Add A - move to right to remove A

Remove C - move to right to add C

In industry to increase yield:

Keep adding reactant

Keep removing product

Change of pressure:

-Only applies with gases - gas causes pressure - more gas= more pressure

Increasing pressure moves the equilibrium to the side with the fewer gas particles

Change in temperature:

-If forward reaction is exothermic, the backwards reaction is endothermic

-In this case an increase in temperature - equilibrium moves left to reduce temperature because reaction is endothermic

Change in Concentration:

Increasing the concentration of the reactants will favour the reaction that produces the produce as more molecules are available to react. it will increase the yield of the products. likewise, decreasing the concentration of products will favour the reaction that reforms the reactants.

Catalysts

Have no effect on position of equilibrium because it speeds up the back and forwards reaction equally - system will reach equilibrium faster

Page 3

Equilibrium constant -Kc

In an acid and alkaline reversible reaction you can work out the concentrations when equilibrium is reached by doing titrations until the concentrations stay the same

For a reaction : aA + bB == xX + yY

Kc = [X]^x[Y]^y

[A]^a[B]^b

Remember to calculate the units

Changing equilibria conditions - Kc

Kc tells us the position of equilibria

Kc< 1 - equilibrium is to the left

Kc>1 - equilibrium is to the right

Kc is temp dependent, increase temp - equilibrium moves left and Kc increases

Changing concentration or pressure has no overall effect on Kc

Temperature - is the only thing that changes equilibrium permanently

Catalysts have no effect on Kc