[AngelShare]

Determine the number of grams of NH3 produced by the reaction of 3.5g of hydrogen gas with sufficient nitrogen gas. (Check for diatomic elements). Use the flowchart below for help.

Given quantity in grams--> change to moles----> multiply by ratio from balanced equation -----> convert wanted quantity from moles to grams.

I've been working on this for about eight or nine days now and I'm still a bit confused. We were assigned just two problems...I got the first one right but I got the second one wrong. I can resubmit it so I'm trying to figure out where I went wrong.

Step One: Convert grams to moles

3.5 grams * 1 mole/2.02 grams
1.7 moles

Step Two: Multiply my answer by the molar ratio

1.7/1 * 2/3

1.1 moles

Step Three: Convert from moles to grams

I stopped here because I wanted to make sure I had everything right up until this point as I'm not really sure of where I messed up. This is what I was told, "#2 is correct in the first part.  In the second part use the molar ratio from the coefficients in the original equation and then use the molar mass (g) of NH3.  The molar mass should be 2/3." Since then, I've tried to fix it up so what I have done might be right so far or it may still be off.

[madscientist]

Ive bypassed some of the steps in your flow chart but from this you should be able to work the question out, do me a favour though show me all your working wether you think its right or not because you seem to have done everything right so far? maybe they want more significant figures so dont round of your values at least not until the final result.

3H_2(g) + N_2(g) -----> 2NH_3(g)

                N2 in excess
3mol H₂ ------------------> 2mol NH_3(g)


                  N2 in excess  
6.0474g H_2(g) ------------------> 34.0608g NH_3(g)


                 N2 in excess
3.5g H_2(g) ----------------> ? g NH_3(g)


( 34.0608g / 6.0474g ) * ( 3.5g ) = 19.72g NH_3(g)


If anyone can see anything wrong with my working can they point it out because ide hate to stear this person in the wrong direction.

Cheers,

madscientist :albert:
 

[madscientist]

To do it the way there asking:

molar ratio = 2/3

(2/3) * 1.7 mol H_2(g) = 1/2/15 mol NH_3(g)
                                                 
                              = 1.1333333333333... mol

Therefore:

( 1/2/15 mol NH_3(g) ) * ( 17.0304 g/mol NH_3(g) ) = 19.30112 g NH_3(g)

[AngelShare]

Step One: Convert grams to moles

3.5 grams * 1 mole/2.02 grams
1.7 moles

Step Two: Multiply my answer by the molar ratio

1.7/1 * 2/3

1.1 moles

Step Three: Convert from moles to grams

1.133333333 moles/1 * 17.031/1 moles

19. 3018 grams

Is that right?

[xiankai]

yep.