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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  • Created on: 03-01-12 18:33
Preview of GCSE Chemistry Unit 2 - Endo/Exothermic reactions, Haber process, electrolysis & the pH scale.

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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 · 5H 2O This is a test for water ­ it turns white
anhydrous copper sulphate blue.
Temperature in the Haber Process
o Raising the temperature favours the
endothermic reaction as it absorbs the
excess heat. The yield of ammonia is reduced.
o Reducing the temperature favours the forward reaction because it produces
heat to supply the lack thereof in the environment. The yield increases.
Pressure in the Haber Process
There are 4 gas molecules of reactants and 2
of products. When the pressure is increased, the
forward reaction is favoured as 2 molecules occupy less space than 4 molecules.
The yield is increased.
Optimal Conditions in the Haber Process
We would expect it to be low temperature and high pressure. However
o at low temperature it takes weeks to reach equilibrium
o at high pressure the reaction vessel is dangerous and expensive
Therefore the compromising conditions are 450°C and 200atm, which give a
reasonable yield at a reasonable rate, which is most importantly safe.
If a reaction uses nonvigorous conditions like these, less energy is used
and released into the environment ­ important for sustainable development and also
less expensive, as there are less CO² emissions and thermal pollution (which can
kill fish in lakes due to denaturing of enzymes and lower oxygen content in water).

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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 give
them away. The positive
ions are attracted and
collect electrons to form Cu
atoms. These stick to the
cathode the Cu2+ has been
reduced.…read more

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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 tap water, used for making bleach, PVC & disinfectant)
o sodium hydroxide (used to make soap, paper & ceramics)
Purification of Copper
The copper is reduced by carbon
and purified by electrolysis.…read more

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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 and a nonmetal ion) and water.
e.g. 1 H Cl + N aOH NaCl + H 2O
e.g. 2.…read more

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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
reaction occurs to for a solid to be filtered off
C uCl2 + Na2CO3CuCO3 + 2NaCl
Ammonia into Fertiliser
Ammonia is an alkaline gas which dissolves in water to form hydroxide ions ­ an
alkaline solution.…read more


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