GCSE Chemistry Unit 2 - Endo/Exothermic reactions, Haber process, electrolysis & the pH scale.

Fairly comprehensive notes covering a wide range of the unit 2 specification, including;

  • endothermic and exothermic reactions
  • the Haber process
  • electrolysis of copper
  • electrolysis of brine
  • acids and alkalis 
  • the pH scale.

Created for the AQA 2011 unit 2 exam. Any changes to the specification since that point are not included - check before you revise.

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Page 1

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Exothermic and Endothermic Reactions

In a reversible reaction, if the forward reaction is exothermic, the backwards is
endothermic, such as in copper sulphate and water
If the blue crystals are heated, they take in
heat. If we add water, it will become hot.
CuSO4 + H 2
O CuSO4 ·…

Page 2

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REDOX Reactions

REDOX reactions involved REDuction and OXidation.
o Oxidation is gain of oxygen and loss of electrons.
o Reduction is loss of oxygen and gain of electrons.
We can remember this in OILRIG Oxidation Is Loss, Reduction Is Gain.


The cathode is rich in
electrons and wants to…

Page 3

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Electrolysis of Brine [NaCl]

At the cathode
2H + + 2e- H 2

At the anode
2Cl- - 2e- Cl2

The entire equation
2NaCl + 2H 2O H 2 + Cl2 + 2NaOH

Products include
o hydrogen (used for making ammonia & hydrogenation of margarine)
o chlorine (kills bacteria in…

Page 4

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o They migrate to the cathode where they gain electrons. Impurities collect at the

The pH Scale

The pH scale measures how acidic or alkaline a solution is. Neutralization
occurs when any acid reacts with an alkali to produce a salt (any ionic compound
made from a metal ion…

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e.g. 2 K + H NO3KNO3 + H 2O


If a salt does not dissolve, it is an insoluble salt or precipitate. These can be very
useful in industry some waste from factories contains dissolved transition metals,
which can harm the environment. When sodium carbonate is added, a precipitation…


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