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### Topic: mole calculation  (Read 631 times)

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#### Emeritt

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##### mole calculation
« on: November 29, 2023, 01:53:28 PM »
I need urgent help with mole calculation.

0.1 mole of ammonia reacts with 0.1 mole of oxygen gas to give nitrogen monoxide and water:

4NH3(g) + 5O2(g)  4NO(g) + 6H2O(l)

What is the number of moles of nitrogen monoxide produced? I need to see calculation of it in detail.
Many thanks.

#### Borek

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##### Re: mole calculation
« Reply #1 on: November 30, 2023, 02:40:29 PM »
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#### Emeritt

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##### Re: mole calculation
« Reply #2 on: November 30, 2023, 10:28:49 PM »

I figured out that 4 moles of ammonia is needed to react with 5 moles of oxygen to give 4 moles of NO. now it is 0.1 mole, which is 2% of 5moles, so it should take 0.08 mole of ammonia and the amount of NO produced should be 0.08 mole. but there is no "0.08 mole" in the answer of this MC question.
In addition which one is limiting reagent? Ammonia or oxygen?

#### Borek

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##### Re: mole calculation
« Reply #3 on: December 01, 2023, 03:18:50 AM »
I figured out that 4 moles of ammonia is needed to react with 5 moles of oxygen to give 4 moles of NO.

OK, that's one of the ways of reading what the balanced reaction equation says.

Quote
now it is 0.1 mole, which is 2% of 5moles,

Beware: when you say "it is 0.1 mole" we have no idea 0.1 mole of what, as there are two substances with the same amount given in the problem. Later you refer to 5 moles, so we can guess you meant O2, but you should never assume people will guess right.

Quote
so it should take 0.08 mole of ammonia and the amount of NO produced should be 0.08 mole.

Assuming you meant "0.1 mole of oxygen" above - yes.

Quote
but there is no "0.08 mole" in the answer of this MC question.

Which looks like an error in the test.

Quote
In addition which one is limiting reagent? Ammonia or oxygen?

The best approach to finding the limiting reagent is to do the calculations several times, separately for each of the reagents with given initial amount.

How many moles of ammonia would react with 0.1 moles of oxygen? Is there enough ammonia?

How many moles of oxygen would react with 0.1 moles of ammonia? Is there enough oxygen?
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#### Emeritt

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##### Re: mole calculation
« Reply #4 on: December 01, 2023, 11:30:23 AM »
I figured out that 4 moles of ammonia is needed to react with 5 moles of oxygen to give 4 moles of NO.

OK, that's one of the ways of reading what the balanced reaction equation says.

Quote
now it is 0.1 mole, which is 2% of 5moles,

Beware: when you say "it is 0.1 mole" we have no idea 0.1 mole of what, as there are two substances with the same amount given in the problem. Later you refer to 5 moles, so we can guess you meant O2, but you should never assume people will guess right.

Quote
so it should take 0.08 mole of ammonia and the amount of NO produced should be 0.08 mole.

Assuming you meant "0.1 mole of oxygen" above - yes.

Quote
but there is no "0.08 mole" in the answer of this MC question.

Which looks like an error in the test.

Quote
In addition which one is limiting reagent? Ammonia or oxygen?

The best approach to finding the limiting reagent is to do the calculations several times, separately for each of the reagents with given initial amount.

How many moles of ammonia would react with 0.1 moles of oxygen? Is there enough ammonia?

How many moles of oxygen would react with 0.1 moles of ammonia? Is there enough oxygen?

Limiting reagent is the one that is completely used up first.
According to the equation, 0.08 mole of ammonia is needed to react with 0.1 mole of oxygen.
Oxygen should deplete first and 0.02mole of ammonia should remain, so I think oxygen is the limiting reagent.
On the other hand, 4 x 1.25 = 5.0, so 0.1 x 1.25 = 0.125 mole of oxygen would be needed to react with 0.1mole of ammonia,  which means there is not enough oxygen to react with all the ammonia

#### Borek

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##### Re: mole calculation
« Reply #5 on: December 01, 2023, 01:47:59 PM »
Limiting reagent is the one that is completely used up first.
According to the equation, 0.08 mole of ammonia is needed to react with 0.1 mole of oxygen.
Oxygen should deplete first and 0.02mole of ammonia should remain, so I think oxygen is the limiting reagent.
On the other hand, 4 x 1.25 = 5.0, so 0.1 x 1.25 = 0.125 mole of oxygen would be needed to react with 0.1mole of ammonia,  which means there is not enough oxygen to react with all the ammonia

Yep.
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