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April 19, 2014

Posted by **Mandy** on Thursday, December 8, 2011 at 10:54pm.

N2(g) +3H2 (g)(arrow) 2NH3(g)

- AP CHEMISTRY NEED HELP PLEASE -
**DrBob222**, Thursday, December 8, 2011 at 11:33pmHere is a worked example of a stoichiometry problem but you don't need to go through conversion to moles since the problem starts with moles. But here it is.

http://www.jiskha.com/science/chemistry/stoichiometry.html

All you need to do is to convert 0.1 mole H2 to N2.

0.1mol H2 x (1/3) = mole N2.

Then remembering that 1 mole N2 occupies 22.4 L at STP, convert to L.

- AP CHEMISTRY NEED HELP PLEASE -
**Mandy**, Thursday, December 8, 2011 at 11:46pmI am sorry, I must be really tired. I am not getting this. Have a huge exam tomorrow and am stuck on this right now. Why am I multiplying by 1/3 ? I know this must sound silly to you but can you please explain this again. Thank You

- AP CHEMISTRY NEED HELP PLEASE -
**Mandy**, Friday, December 9, 2011 at 12:25amMy answer is 0.672? Is this correct? Thank You

- AP CHEMISTRY NEED HELP PLEASE -
**DrBob222**, Friday, December 9, 2011 at 1:27amYou must convert moles H2 to moles N2. You do that using the coefficients in the balanced equation. The equation TELLS you that it takes 3 moles H2 for each mole N2; i.e., 1/3 mol N2 = 1 mole H2 so 0.1 mole H2 will require 1/3 of that or 0.0333 moles N2.

No, your answer isn't right and I know what you did wrong. You divided 0.1/3 and read the first digit only (or your calculator rounded to the first digit) and you let the others go. 0.1/3 = 0.333 and that x 22.4 is 0.7 something. When I calculate ANYTHING, I never copy it onto paper and re-enter it in the calculator later. I let that number sit in the calculator and use it again as needed. That way, whatever is in the calculator (too many digits and more significant figures even than I'm allowed) just sits there. I round at the end of the problem to the right number of significant figures.

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