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### Topic: Limiting reagent question involving diagram.  (Read 17805 times)

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#### narutodemonkill

• Regular Member
•   • Posts: 56
• Mole Snacks: +0/-2 ##### Limiting reagent question involving diagram.
« on: February 03, 2010, 04:48:15 PM »
practice exam question.
The illustration to the left represents a mixture of nitrogen (blue) and oxygen (red) molecules. ( I counted 6 oxygen molecules and two nitrogen molecules)

If the molecules in the above illustration reacts to form N2O4 according to the equation
N2 + 2O2-->  N2O4

1. the limiting reagent is?... well I assumed molecules and mols would be interchangeable, so I used the ratio method
1 molecule of N204 is formed for 1 molecule of N2  1:1

and 1 molecule of N204 is formed for 2 molecules of O2 1:2
6O2 * 1/2= 3 molecules of N2O4

2 N2 * 1 = 2 molecules of N2O4

so from the above i deduced that N2 was the limiting reagent.

2. the number of N2O4 molecules formed is.. 2 because All of the N2 reactant is used up at this time.

3. the number 02 molecules in excess?
Here I hit a roadblock, normally in these types of questions without diagrams, I would just convert mols of reactant to mols of exess reactant and subtract this from the initial amount of that reactant.

So one of the main questions I have is in theses types of questions are mols and molecules interchangeable?
or do you still use avogadros constant to convert.

#### narutodemonkill

• Regular Member
•   • Posts: 56
• Mole Snacks: +0/-2 ##### Re: Limiting reagent question involving diagram.
« Reply #1 on: February 03, 2010, 04:52:44 PM »
practice bonus exam question.
The illustration to the left represents a mixture of nitrogen (blue) and oxygen (red) molecules. ( I counted 6 oxygen molecules and two nitrogen molecules)

If the molecules in the above illustration reacts to form N2O4 according to the equation
N2 + 2O2-->  N2O4

1. the limiting reagent is?... well I assumed molecules and mols would be interchangeable, so I used the ratio method
1 molecule of N204 is formed for 1 molecule of N2  1:1

and 1 molecule of N204 is formed for 2 molecules of O2 1:2
6O2 * 1/2= 3 molecules of N2O4

2 N2 * 1 = 2 molecules of N2O4

so from the above i deduced that N2 was the limiting reagent.

2. the number of N2O4 molecules formed is.. 2 because All of the N2 reactant is used up at this time.

3. the number 02 molecules in excess?
Here I hit a roadblock, normally in these types of questions without diagrams, I would just convert mols of reactant to mols of exess reactant and subtract this from the initial amount of that reactant.

I will try to attempt it. 2 molecules of N2O4 *( 2 molecules of oxygen /1 molecule of N2O4) so 4 molecules of oxygen are used up in reaction therfore 2 are in excess ?

So one of the main questions I have is in theses types of questions are mols and molecules interchangeable?
or do you still use avogadros constant to convert.

is there a different way to this question