How many moles of NO are required to completely react with 2.45 mol NH3

Answer 1

Hello, Mason,

The primary challenge here is balancing the equation.

NO + NH₃ = N₂ + H₂O

Were to start? Well, we know that we need for the N atroms to come in pairs, since the N₂ is the only place it can go. So we;\'re constrained to even whole numbers of NO. If I pencil in a coefficient of 2 for the NO, we spot the next problem. Hydrogen atoms come in groups of 3 (from the NH₃). Since the only product containing H is H₂O, we'll need to add coefficients to NH₃ that make the number of H's even, so the numbers 2, 4, 6, etc. are all possibilities. But since we need at least 2 NH₃ groups to get to the first even number of H atoms, that will require at least 3 H₂O molecules, just to account for the H's coming in. BUT, changting NO to 3 creates an odd number of N atoms, which we already know we can't handle.

NO + 2NH₃ = N₂ + 3H₂O : = Doesn't work. H's are OK, but there are 3 N atoms coming in, and they need to leave in pairs (N₂).

At this point we'll cheat, just for a few minutes. Let's use fractions to get to a balanced equation. Start by putting a coefficient of 2 on the NH₃ to generate 2 N and 6 H atoms. Since we have 6 H atoms, we'll need 3 H₂O molecules to use them all, so put a coefficient of 3 for the H₂O. That combination produces 5 nitrogen atoms, but it can only leave in pairs, via N₂. Make sure no one is looking and put 2.5 as the N₂ coefficient. That produces 5 N atoms, just what we need to balance the equation!

3NO + 2NH₃ = 2.5N₂ + 3H₂O

That seems to balance N: 5 in and 5 out O: 3 in and 3 out H: 6 in and 6 out. BALANCED

But we can't have 1/2 of a molecule. What we CAN do, however, is multiply all the coefficients by the lowest number that will make them all whole numbers, in this case, 2.

6NO + 4NH₃ = 5N₂ + 6H₂O

That looks balanced. Check it to be certain. [10 N, 6 O, and 12 H on both sides] This is a great way to get past the initial block or trying to get everything right the first time. Just make it work, and then factor up to whole numbers.

The question wants to know how much NO we need to react with 2.45 moles of NH₃. The molar ratio of NO to NH₃ is 6 to 4. We need 6 moles NO for every 4 moles NH₃. That's a molar ratio of 1.5.

We need (1.5 moles NO/mole NH₃)*(2.45 moles NH₃) = 3.675 moles NO

We need 3.68 moles of NO (to 3 sig figs).

Bob

Note: NO is nitric oxide. N₂O is nitrous oxide, also known as laughing gas. But they are wrong. Laughing gas is He He He He He