Chemical Equation Help?

Question

Vehicles which run on fuel cell technology are currently being developed. These vehicles are quiet and efficient and make use of two plentiful elements - hydrogen and oxygen.

Fuel cells generate energy to power the vehicle by combining hydrogen gas (H2) and oxygen gas (O2) to form water (H2O) as shown in the following chemical equation.
2 H2+O2 ==> 2 H2O

If a fuel cell-powered vehicle can hold a maximum of 5 kg of water (i.e., the product), what is the maximum total amount of hydrogen and oxygen gas that should be used as reactants?


So if anyone could help, it'd be much appreciated.
If you can make me understand it, when I can, I'll give you the 10 points.
:3

Klimbim, thank you.

You'll receive them as soon as this time runs out.
^ ^;

Answer 1

First calculate how many moles 5kg of water is
M=16g/mol
n=5000g/18g/mol
n=277.78mol

From the reaction: 2 H2+O2 ==> 2 H2O
2 moles of water come from 2 moles of hydrogen and 1 mole of oxygen
therefore you need a max amount of 277.78mol hydrogen and half that of oxygen (138.89mol).
M(O2)=32g/mol -> m=138.89mol*32g/mol=4444.44g Oxygen
M(H2)=2g/mol -> m=277.78mol*2g/mol=555.56g Hydrogen

Answer 2

Here's a different approach for you.
The equation tells you that you need four atoms of H and two atoms of O to make two molecules of H2O. You also know that you can only hold a total of 5000grams of water after all the H2 and O2 has reacted. The molecular weight of water is 18 grams per mole, so that means the 5000 grams of water contain (5000 / 18) = 277.78 moles of water. Okay so far?
Going backwards in the equation now, if you have 277.78 moles of water, you must have started with 277.78 moles of O atoms. But the O atoms are in the form of oxygen molecules, or O2. So the 277.78 moles of O atoms make up 138.89 moles of O2 molecules. The molecular weight of O2 is 32 grams per mole, so that means there must have been (138.89 x 32) = 4444.4 grams, or 4.4444 kilograms of O2.
The rest of the 5 kilograms had to come from the H2. That means there must have been (5000 - 4444.4) = 555.6grams, or 0.5556 kilograms of H2.

Answer 3

Ok so the problem tells you that 5 kg is the maximum amount of H20 can be held in the vehicle.
H2: for 1 mole of H2, you get 1 mole of H20. The ratio is 1:1
O2: for 1 mole of O2, you get 2 moles of H20. The ratio is 1:2
So you need 5 Kg of H2 (1:1). and 2.5 Kg of O2 (1:2).
Hope that makes sense :-)

Answer 4

first convert 5kg H2O to moles H2O
5kg H2O * (1 kmol H2O / 18 kg H2O) = 0.278 kmol H2O = 278 moles H2O

from the reaction equation,
for every 2 moles of H2O produced, 2 moles of H2 and 1 mole of O2 is consumed

so moles of H2 consumed =
moles of H2 = 278 moles H2O * ( 2 moles H2 / 2 moles H2O)= 278 moles of H2

moles of O2 consumed =
moles of O2 = 278 moles H2O * (1 mole O2 / 2 moles H2O)
= 139 moles O2

convert moles H2 and O2 to grams
278 moles of H2 * (2 grams H2 / mole H2)
= 556 grams H2

139 moles of O2 * (32 grams O2 / mole O2)
= 4448 g O2