1. When
burn they react with
and release or give out lots of
energy (e.g. in a power station) and is called an
reaction.
2. Reactions which take in energy, perhaps causing a cooling effect, are called
reactions.
3. Most fuel molecules are made of (i) carbon and (ii) hydrogen and after complete burning they are changed to (i)
gas and (ii)
to give liquid
.
4a. The gas can be detected by bubbling it into
which turns '
'.
4b. The liquid can be detected by (i) changing cobalt chloride paper from
to
OR (ii) by changing anhydrous copper sulphate from
to
.