Chemistry homework??

Question

When ammonium nitrate explodes it forms nitrogetn gas, oxygen gas, and water. When 40 grams of ammonium nitrate explode, 14 grams of nitrogen and 8 grams of oxygen are formed. How many grams of water are formed?

How can I figure out the answer to this? I'm not asking for the answer...just how to figure it out.

thanks!

Answer 1

14 (of nitrogen + 8 (of oxygen) + x (of water) = 40

14 + 8 + x = 40

X = ????

Answer 2

There are two ways to do this:

1st, the easy way, just do reactant - products.  Since matter cannot be destroyed, the reactant must have the same mass as the products.  So just do 40g ammonium nitrate -14g N - 8g O, which equals 18g of water.

or you can do it the hard longer way...

you must divide the grams of each substance by the molar mass. so you would get 1/2 mole of ammonium nitrate (NH4NO3) forming 1 mole of nitrogen gas, 1/2 mole of oxygen, and x moles of water.

so, you have: 0.5NH4NO3 => 1N + 0.5O + xH2O

since N appears twice in NH4NO3, in 0.5 moles of NH4NO3, there is 1 mole N. so the N can cancel out, leaving you with: 0.5H4O3 => 0.5O + xH2O.

If you multiply the subscript numbers by the coefficient, you get 2 moles of H and 1.5 moles of O. there is 0.5 moles of O on the other side, so when you cancel out the O, you have: 2H + O = xH2O. so therefore, you will have only 1 mole of water, which has a molar mass of 18 grams.  So 18 grams of water will form