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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Rodeocrazy1 on February 12, 2006, 10:48:19 PM

Title: balancing chemical formulas
Post by: Rodeocrazy1 on February 12, 2006, 10:48:19 PM

I am having trouble balancing chemical formulas.  I get some but  the ones like  N + H  reacting to  NH3    equalling N2 + 3H2  = 2NH3  I do not understand how this works.  Can someone please explain.  Cj

Title: Re:balancing chemical formulas
Post by: Mr T on February 13, 2006, 02:48:03 AM

have a look at the periodic tabe, N is in the 5th column. That means N has 5 valence electrons. So to obey the octet rule it has to gain ( share in this case) 3 electrons from 3 H atoms.

Title: Re:balancing chemical formulas
Post by: Borek on February 13, 2006, 04:48:47 AM

Quote from: Rodeocrazy1 on February 12, 2006, 10:48:19 PM

I am having trouble balancing chemical formulas.  I get some but  the ones like  N + H  reacting to  NH3    equalling N2 + 3H2  = 2NH3  I do not understand how this works.  Can someone please explain.  Cj

You mean formulas or reaction equations?

Title: Re:balancing chemical formulas
Post by: AWK on February 13, 2006, 06:59:31 AM

You can solve this problem in pure algebraic way counting atoms.
a(2N) + b(2H) = c(N+3H)
You should solve the problem in integers.
Putting tentatively a=1 we have 2=c and 2b=3c from which b=3.
Finally chemical equation (in molecules)  should be:
N2 + 3H2 = 2NH3

or analogously:
putting b=1 we have 2=3c => c=2/3 and a=1/3
(1/3)N2 + H2 = (2/3)NH3
and finally
N2 +  3H2 = 2NH3

and so on