A)Write the molecular equation for the oxidation in air of (i) Iron to
iron (II) oxide, (ii) Iron (II) oxide to iron (III) oxide
and for (ii) give in terms of electron transfer both the oxidation and
reduction half equation
B) Describe how ammonia can be used as a refrigerant

Hello Paulinej

A)
i)   2Fe + O2 -> 2FeO
ii)  2Fe + 3O2 -> 2Fe2O3
iii) Fe2+ + 2e- -> Fe
     O2 + 2e- -> 2O-
     Fe3+ + 3e- -> Fe

B) The process of converting liquid ammonia to gaseous ammonia is an
endothermic reaction.  An endothermic reaction requires heat to make
it start.  At its most simplest form in a refrigerator, ammonia gas is
compressed to a liquid and then circulated around pipes at the back of
the refrigerator, as the liquid evaporates to a gas it cools the
fridge.  The refrigerator is cooled because heat is taken from inside
the refrigerator to convert the ammonia from liquid form to a gaseous
form.

Further information on this can be found here:
http://encarta.msn.com/encyclopedia_761559433/Refrigeration.html
http://www.chillertrader.com/articles.php?id=2

ii)  4Fe + 3O2 -> 2Fe2O3
iii) O2 + 4e- -> 202-