It is, in fact, possible to combine hydrogen and
oxygen to make water, but it's a little tricky.
Oxygen is usually present as O2 (two oxygen
atoms bonded together), so in order to make water
(H2O) the two oxygen atoms in O2 must break apart,
and that takes extra energy. This energy can come
from a couple places. Adding heat (like a spark)
will give the necessary energy to get the reaction
started so a couple O2 molecules to break into 2
oxygen atoms and bond with H2 to make a few water
When these molecules form, it
generates more heat (it's an"exothermic"
reaction), and this heat allows a few more O2
molecules to break into oxygen atoms and form a
few more molecules of water can form,generating
more heat... etc.
A way to see water forming
from oxygen and hydrogen in a lab (which should
only be done with a science teacher supervising)
is to do a"hydrogen pop" test. You can use a
small upside-down test tube to collect hydrogen
gas, then hold a lit match at the mouth and you'll
hear a popping sound. The heat allows the
hydrogen to combine with the small amount of
oxygen in the air. When you look in the test tube
afterwards there will be water condensed on the
Hope that answers your question!