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Chemical Equilibrium

Dynamic Equilibrium: a system is in dynamic equilibrium when the forward and reverse
reactions occur at the same rate.

Not all reactions proceed to completion
Some end up with a mixture of reactants and products
This is because some reactions are reversible, where products can be converted

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Effect of concentration
Consider the equilibrium

2CrO42-(aq) + 2H+ (aq) Cr2O72-(aq) + H20(l)

Adding more acid increases the concentration of H+ ions, so the system will try and
minimise this effect but decreasing the concentration of H+ ions and the position of
equilibrium will move to the right, forming more…

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Acids and alkalis
-An Acid is a proton (H+) donor.

-An alkali (base) is a proton (H+) acceptor.

When acid is added to water, it releases protons.

When aqueous bases/alkalis are added to water, a hydroxide ion forms (OH-.)

Acids and alkalis react in neutralisation reactions. In solution the hydroxide…

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Sea Water
About half of the carbon dioxide formed by burning fossil fuels dissolves in the oceans.
The pH of sea water remains fairly constant at a value between 7.5 and 8.5.. Its pH is
maintained by the buffering action of dissolved carbon dioxide, hydrogencarbonate and
carbonate ions.

An increase…

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Titration Calculations
Example 1

20.0cm3 of sulphuric acid was exactly neutralised by 24.0cm3 of 0.950 mol dm-3 aqueous
sodium hydroxide. Calculate the concentration of the acid,

H2SO4 + 2NaOH Na2SO4 + 2H20

a) Calculate the amount, in moles, of NaOH that reacted
n= c x v = 0.95 x 0.024…


Sophie Thomas


Absolutely fantastic.

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