When 2 moles of ammonia (NH3) decomposes into nitrogen gas (N2) and hydrogen gas (H2), how many moles of NITROGEN gas are produced?
1 mole
2 moles
3 moles
4 moles
I was thinking 2 moles?
2 NH3 ===> N2 + 3 H2
one molecule N2 for every TWO NH3 molecules
so
ONE MOL N2 for every two MOLS NH3
Avagado's number is like a dozen except 6*10^23 instead of 12
for every 2 dozen NH3 s You get 1 dozen N2 s
So it’s only 1?
Yes. 2 mols NH3 will give you 1 mol N2. Look at the coefficients. That TELLS you that
2 NH3 ==> 1 N2. To go further, a complete math explanation looks like this and this method will convert mole of ANYTHING to mole of ANYTHING.
2NH3 ==> N2 + 3H2.
I want to convert 2 moles NH3 to ? moles N2? Mathematically it's done this way using the coefficients in the balanced equation.
2 moles NH3 x conversion factor = moles N2. You see the conversion factor is just a ratio of the coefficients of the unknown mole/known mole.
2 mols NH3 x (1 mol N2/2 mols NH3) = 1 mole N2 produced.
You may wonder how I know to put moles N2 on top and moles NH3 on the bottom? Easy. We're converting NH3 to N2 so we want the units of NH3 to cancel and leave units of moles N2. You will see moles NH3 in the numerator cancel with those in the denominator and it leaves moles N2 as the unit and that's was we want.
Of course on simple cases like this you don't need to go through the math every time because it's obvious that 2 NH3 gives 1 N2. Look at
KMnO4 + 5FeCl2 + 8HCl --> MnCl2 + 5FeCl3 + 4H2O + KCl which is slightly more complicated. We ask how many moles FeCl3 are produced for 5 moles FeCl2. Of course the answer is 5. But the answer isn't so obvious if we ask how many moles H2O do we get from 14.5 moles FeCl2. Then I would do
14.5 mols FeCl2 x (4 molsl H2O/5 moles FeCl2) = 14.5 x 4/5 = ?
Isn't chemistry FUN !!!