Stoichiometry

[magaly79]

Hi I need help with a Stoichiometry problem. I am complete lost.

I don't know where to start, or how to to solve.

2H2 + O2 -2H2O. I know the formula balances and that is it.

The questions is How many grams of H2O are produced when 2.5 moles of O2 are used?

Thanks!

[darkwatcher]

look at this
http://www.youtube.com/watch?v=FzU0udv8PA4&feature=channel

[Borek]

Limiting reagents have nothing to do with this question.

The shortest introduction to stoichiometry (http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations).

[MustBe]

Well you know how many moles of 02 you have.
So in order to figure out how many moles of water this will make, you need to use the stoichiometric proportions.
The equation tells you that for every one mole of O2 you will get 2 moles of H20
so multiply 2.5 moles 02 by 2.
now, knowing you have 5 moles of H2O, calculate its mass by using the equation
moles= mass/molar mass

A hint to starting stoich problems is to always calculate your number of moles of the reacting agent, and then convert it into the number of moles of the product. From there you can answer almost any question.
Good Luck!