AS Level Haber Process question

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AS Level Haber Process question

Postby Spen » Mon Nov 02, 2009 7:34 pm UTC

Taken from my homework:
In the haber process, nitrogen reacts with hydrogen to form ammonia.
A. Write a balanced symbol equation for the reaction.
N2+ 3H2= (replacing a reversible equation arrow) 2NH3
b. Calculate the maximum yield of ammonia that could be made if 1.4 tonnes of nitrogen reacted with excess hydrogen.
1:2 ratio of nitrogen to ammonia
0.1*17= 1.7 tonnes
C. the actual yield of ammonia was 3.8 tonnes. Calculate the % yield of ammonia in the reaction.
I've done this question 5 times over trying to figure out what's wrong with my answer and I keep on getting a 224% (3 Sig. Figs.) yield, what the hell am I doing wrong?
Help would be much appreciated!
Thanks in advance

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Re: AS Level Haber Process question

Postby Charlie! » Mon Nov 02, 2009 11:37 pm UTC

If the actual yield is larger than your theoretical yield, something is definitely up.

And you're definitely not going to turn 1.4 tonnes of nitrogen into 3.8 tonnes of ammonia. Was it 14 tonnes of nitrogen? 0.38 of ammonia? Something silly like that?
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Re: AS Level Haber Process question

Postby Minchandre » Tue Nov 03, 2009 2:56 am UTC

Your math is correct; 1.4 tons of nitrogen makes 1.7 tons of ammonia.

Your percent yield, therefore, is somewhat more than 200%! Someone needs to patent that method.

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Re: AS Level Haber Process question

Postby Spen » Tue Nov 03, 2009 1:12 pm UTC

I've read and reread the question, and shown it to to my friend who's taking chemistry for A2, he said it was utter bollocks.
I managed to find my teacher this morning and said that the question was a load of bollocks and had no answer...

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Re: AS Level Haber Process question

Postby bigglesworth » Tue Nov 03, 2009 1:16 pm UTC

Maximum yield is always 100%, by definition, surely.

Your yield is the percentage of that maximum. If the maximum is 1.7 tonnes (make sure to write tonnes in your exams, tons aren't used in A levels any more), and you get one tonne, the yield is 59%.
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