Ethanol, C2H5OH burns with oxygen in air to give carbon dioxide and water. what is the amount (in moles) of water produced from 0.51 mol...

This is an example of a combustion reaction.  To answer
this you must first balance the equation.

The easiest way
is to set up the reaction equation without any
coefficients:

C2H6O + O2 -->  CO2  +
HOH

Now start balancing, first with carbon, then with
hydrogen and last the oxygen.

There are 2 carbons on the
left  and 6 hydrogens so you add a coefficient of 2 in front of the CO2 and a 3 in front
of the water.

C2H6O  +  O2 -->  2 CO2  +  3
HOH

Now count the number of oxygen on the product side and
you get seven.  One oxygen came from the ethanol so you need 6 more from oxygen. Add a
coefficient of 3 in front of the oxygen on the reactant side and your reaction is
balanced.

C2H60  + 3 O2  -->  2 CO2  +  3
HOH

This shows you that for every mole of ethanol, you will
get 3 moles of water.  So if you start with 0.51 moles of ethanol, you will produce 3 x
.51 or 1.53 moles of water.