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Specialty Chemistry Forums => Chemical Education and Careers => Topic started by: Borek on April 13, 2006, 11:15:50 AM

Title: going in circles when balancing equation
Post by: Borek on April 13, 2006, 11:15:50 AM: I need an example of such situation - unfortunately whenever I try I am just balancing, can't locate a loop. I am just too good ;)
Title: Re: going in circles when balancing equation
Post by: woelen on April 13, 2006, 02:48:15 PM: ?? ???
Title: Re: going in circles when balancing equation
Post by: Borek on April 13, 2006, 02:56:57 PM: When somebody not fluent in equation balancing starts to work on some 'complicated' case it sometimes end in a circle - "to balance A atoms I have to modify B coefficient, in turn there is not enough C atoms and I have to modify D coefficient - which makes my equation lacking A atoms which forces me to modify B coefficient" - and circle closes here.

I just have troubles constructing such example.
Title: Re: going in circles when balancing equation
Post by: Albert on April 13, 2006, 03:16:23 PM: Oh, I think I've got it! You want us to propose you such examples, don't you?
Title: Re: going in circles when balancing equation
Post by: Borek on April 13, 2006, 03:57:52 PM: Yes. I have approached several equations trying to make this mistake but I am too efficient in NOT making it :)
Title: Re: going in circles when balancing equation
Post by: woelen on April 14, 2006, 04:12:41 AM: Try this one. When working with the adjustment method, as you mentioned above, this one is hard:

CH3ONa + NaClO2 + HCl --> COCl2 + NaCl + H2O

Balancing by means of linear algebra methods is easy, but balancing by hand may be quite hard for a beginner.
Title: Re: going in circles when balancing equation
Post by: Borek on April 14, 2006, 04:20:32 AM: Good one, thanks!
Title: Re: going in circles when balancing equation
Post by: Borek on April 14, 2006, 02:03:09 PM: I think I have found a better one - looks much simpler ot first sight:

P₄O₆ -> P₄ + P₂O₄

but is surprisingly hard to balance by inspection.
Title: Re: going in circles when balancing equation
Post by: Alberto_Kravina on April 14, 2006, 02:35:20 PM: I balanced it (I don't post the reaction, I don't want to spoil it ;) ... the other members should try to balance it as well...)
Title: Re: going in circles when balancing equation
Post by: KD00LS on April 14, 2006, 04:38:46 PM: I find it very easy to attempt to balance the molecules with the most amount of elements, then work down to the molecules with the least amount. That way, when you get down to balancing the last molecule, you won't disrupt any other pre-determined coefficients.

I also balanced this, took me under 30 seconds. ;D
Title: Re: going in circles when balancing equation
Post by: Borek on April 14, 2006, 05:25:46 PM: This one will probably take you longer:

P₂I₄ + P₄ + H₂O -> PH₄I + H₃PO₄
Title: Re: going in circles when balancing equation
Post by: pantone159 on April 14, 2006, 07:48:31 PM: Not so hard. I is only on the right in 1 place, so is O, then after that H is only on the right in one unknown place, then you just have to count the P's.
Kind of ugly coeffients though.
Title: Re: going in circles when balancing equation
Post by: KD00LS on April 15, 2006, 02:28:36 AM: I tried for about 10 minutes, I can't figure that last one out. I can't get the ratio of H to O on the product side to be 2:1 like it is on the reactant side.
Title: Re: going in circles when balancing equation
Post by: Mitch on April 15, 2006, 04:45:21 AM: Check Jched, they love comparing methods for these types of things.
Title: Re: going in circles when balancing equation
Post by: Borek on April 15, 2006, 06:15:47 AM: Many of these, although some not directly on the subject:

J.Chem.Educ. 22, 266, 461 (1945). 72, 716, 1125 (1995).
J.Chem.Educ. 36, 215 (1959). 74, 1359 (1997).
J.Chem.Educ. 38, 327 (1961). 65, 45 (1988). 74, 1270 (1997). 76, 362 (1999).
J.Chem.Educ. 69, 276 (1992)
J.Chem.Educ. 23, 550 (1946). 36, 77 (1959). 74, 69 (1987). 76, 362 (1999)
J.Chem.Educ. 38, 329 (1961). 74, 1365, 1365 (1997)
J.Chem.Educ. 62, 507 (1985). 72, 894 (1995).
J.Chem.Educ. 73, 507 (1996). 74, 1367, 1368 (1997).
J.Chem.Educ. 54, 704 (1977). 59, 728 (1982). 69, 279 (1992). 71, 295 (1994). 74, 1369 (1997).
Title: Re: going in circles when balancing equation
Post by: KD00LS on April 15, 2006, 01:27:53 PM: I'll have to snoop around in those files. I'm new to the site so I haven't really explored.
Title: Re: going in circles when balancing equation
Post by: Borek on April 21, 2006, 06:58:26 AM: http://www.chembuddy.com/?left=balancing-stoichiometry&right=toc

Comments welcomed.
Title: Re: going in circles when balancing equation
Post by: Mitch on April 21, 2006, 03:55:16 PM: Page error: http://www.chembuddy.com/?left=balancing-stoichiometry&right=balancing-inspection

XML Parsing Error: mismatched tag. Expected: </p>. Location: http://www.chembuddy.com/?left=balancing-stoichiometry&right=balancing-inspection Line Number 110, Column 5: </div> ----^
Title: Re: going in circles when balancing equation
Post by: Mitch on April 21, 2006, 03:56:47 PM: (2)P4O6 -> (1/2)P4 + (3)P2O4

That was a really easy one by inspection. :)
Title: Re: going in circles when balancing equation
Post by: Mitch on April 21, 2006, 04:14:48 PM: (5/16)P2I4 + (13/32)P4 + (4)H2O -> (5/4)PH4I + (1)H3PO4

The above is also a very easy one for me to do by inspection. Most people will not want to use fractions and will get caught up avoiding them. But if you just run with them and are comfortable enough with them its no big thing. And, then at the end you can multiply by 32 and get a more aesthetically pleasing form.
Title: Re: going in circles when balancing equation
Post by: Borek on April 21, 2006, 04:55:20 PM: Thanks for that </p> tag. For some reason Opera behaves differently than before - instead of stopping of the first error it goes into quirks mode and renders everything, displaying error messages below, that's why I am missing these things now :( Have to check what's going on, perhaps something is wrong with the headers sent (XHTML/HTML)?

As for the equations - I am not stating they are impossible, but they ARE harder than most other examples. But I am open to suggestions - just bear in mind that the equation must fit the screen (that's why I am not using Stout:

10(Cr(N₂H₄CO)₆)₄(Cr(CN)₆)₃ + 1176KMnO₄ + 1399H₂SO₄ -> 35K₂Cr₂O₇ + 1176MnSO₄ + 420CO₂ + 660KNO₃ + 223K₂SO₄ + 1879H₂O

nor Blakley:

88H₂ + 15Ca(CN)₂ + 6NaAlF₄ + 10FeSO₄ + 3MgSiO₃ + 6KI + 2H₃PO₄ + 6PbCrO₄ + 12BrCl + 3CF₂Cl₂ + 20SO₂ -> 6PbBr₂ + 6CrCl₃ + 3MgCO₃ + 6KAl(OH)₄ + 10Fe(SCN)₃ + 2PI₃ + 3Na₂SiO₃ + 15CaF₂ + 79H₂O

nor this nice oxidation example:

10K₄Fe(CN)₆ + 122KMnO₄ + 299H₂SO₄ -> 162KHSO₄ + 5Fe₂(SO₄)₃ + 122MnSO₄ + 60HNO₃ + 60CO₂ + 188H₂O
Title: Re: going in circles when balancing equation
Post by: Mitch on April 21, 2006, 05:13:37 PM: Those look like great extra credit questions for chem studesnts. ::Evil grin::
Title: Re: going in circles when balancing equation
Post by: Borek on April 21, 2006, 05:53:26 PM: K₃[Fe(SCN)₆] + 16Na₂Cr₂O₇ + 58H₂SO₄ -> Fe(NO₃)₃ + 16Cr₂(SO₄)₃ + 6CO₂ + 58H₂O + 16Na₂SO₄ + 3KNO₃

EBAS rulez ;)
Title: Re: going in circles when balancing equation
Post by: Will on May 06, 2006, 08:54:01 PM: I found all the equations above (not Boreks' directly above!) relatively easy. Here are a couple which I had to balance in this year's UK Chemistry Olympiad competition, which I got a Ag in :'( (missed the Au by a couple of marks :'(), but I was happy to get these right :):
NH₃ + NO --> N₂ + H₂O
NH₃ + NO₂ --> N₂ + H₂O
I found them easy but harder than a couple on this page so I thought I might as well mention them!

I came across this equation while messing around with a chemistry experiment simulation program (called CrocChem I think):
Zn + HNO₃ --> H₂O + N₂O + NO + Zn(NO₃)₂
I checked this reaction out online and different reactions happen with Zn and HNO₃ in different conditions, so this equation may not be very accurate. I haven't tried to balance it myself because I've already seen the coefficients so its hard to try to balance it without 'cheating'! I'm sure most of you will find it easy to balance ;).
Title: Re: going in circles when balancing equation
Post by: Borek on May 07, 2006, 04:07:40 AM: Quote from: will17 on May 06, 2006, 08:54:01 PM
Zn + HNO₃ --> H₂O + N₂O + NO + Zn(NO₃)₂

4Zn + 10HNO₃ -> 5H₂O + N₂O + 4Zn(NO₃)₂
3Zn + 8HNO₃ -> 4H₂O + 2NO + 3Zn(NO₃)₂

http://www.chembuddy.com/?left=balancing-stoichiometry&right=balancing-failure

(read the section about KClO₃ and HCl).
Title: Re: going in circles when balancing equation
Post by: lemonoman on May 07, 2006, 04:59:28 AM: Quote from: Borek on April 21, 2006, 04:55:20 PM
88H₂ + 15Ca(CN)₂ + 6NaAlF₄ + 10FeSO₄ + 3MgSiO₃ + 6KI + 2H₃PO₄ + 6PbCrO₄ + 12BrCl + 3CF₂Cl₂ + 20SO₂ -> 6PbBr₂ + 6CrCl₃ + 3MgCO₃ + 6KAl(OH)₄ + 10Fe(SCN)₃ + 2PI₃ + 3Na₂SiO₃ + 15CaF₂ + 79H₂O

I can't imagine a situation in which you'd need to balance this monstrosity. In real life, you only balance single reaction steps and then add them all together to get a big overall equation like this. Or am I wrong?
Title: Re: going in circles when balancing equation
Post by: Borek on May 07, 2006, 06:34:53 AM: Quote from: lemonoman on May 07, 2006, 04:59:28 AM
I can't imagine a situation in which you'd need to balance this monstrosity. In real life, you only balance single reaction steps and then add them all together to get a big overall equation like this. Or am I wrong?

Exam with mad teacher? ;)

I believe it was an example of how efficient algebraic method of equation balancing (http://www.chembuddy.com/?left=balancing-stoichiometry&right=algebraic-method) is, in the paper published by GR Blakley in JCE in 1982 (never seen original paper though so I can be wrong).
Title: Re: going in circles when balancing equation
Post by: Will on May 07, 2006, 09:25:57 AM: Quote from: Borek on May 07, 2006, 04:07:40 AM
4Zn + 10HNO₃ -> 5H₂O + N₂O + 4Zn(NO₃)₂
3Zn + 8HNO₃ -> 4H₂O + 2NO + 3Zn(NO₃)₂

The simulator went for the 2A + B equation! (11Zn + 28HNO₃ --> 14H₂O + 2N₂O + 2NO + 11Zn(NO₃)₂)

I wonder if you asked a group of students to balance: HNO₂ + HN₃ --> N₂ + N₂O + H₂O, how many would come up with: 2HNO₂ + 4HN₃ --> 6N₂ + N₂O + 3H₂O!
Title: Re: going in circles when balancing equation
Post by: lemonoman on May 07, 2006, 12:04:07 PM: Quote from: will17 on May 07, 2006, 09:25:57 AM
I wonder if you asked a group of students to balance: HNO₂ + HN₃ --> N₂ + N₂O + H₂O, how many would come up with: 2HNO₂ + 4HN₃ --> 6N₂ + N₂O + 3H₂O!

Personally, I would not have come up with that answer. I would have stopped right at the beginning, because it's already balanced...

HNO₂ + HN₃ --> N₂ + N₂O + H₂O

2 H , 4 N , 2 O on left side
2 H , 4 N , 2 O on right side
Title: Re: going in circles when balancing equation
Post by: Will on May 07, 2006, 12:25:19 PM: Quote from: lemonoman on May 07, 2006, 12:04:07 PM
Personally, I would not have come up with that answer. I would have stopped right at the beginning, because it's already balanced.

Yup!

Is the 'other' reaction thats happening/could happen: HNO₂ + 3HN₃ --> 5N₂ + 2H₂O?
Title: Re: going in circles when balancing equation
Post by: Borek on May 07, 2006, 01:11:50 PM: HNO₂ + 3HN₃ -> 5N₂ + 2H₂O

4HNO₂ + 2HN₃ -> 5N₂O + 3H₂O

so, for example:

4169HNO₂ + 4637HN₃ -> 5105N₂ + 3935N₂O + 4403H₂O

is correctly balanced ;)
Title: Re: going in circles when balancing equation
Post by: Alberto_Kravina on May 07, 2006, 01:30:54 PM: Quote
4169HNO2 + 4637HN3 -> 5105N2 + 3935N2O + 4403H2O
:o
As lemonoman said, I wonder how many times in in my life (which is most likely going to be a chemist-life ;) ) I'll have to balance such equations... :P
Title: Re: going in circles when balancing equation
Post by: Borek on May 07, 2006, 01:45:38 PM: That's a trick that have nothing to do with chemistry. But looks very seriously chemically :)

You may generate such equations by yourself, just follow description from my lecture on balancing failures (http://www.chembuddy.com/?left=balancing-stoichiometry&right=balancing-failure) :)
Title: Re: going in circles when balancing equation
Post by: Borek on May 16, 2006, 01:29:09 PM: Another interesting one ;)

Pb(NO₃)₂ + Cr(MnO₄)₂ = Pb₃O₄ + Cr₂O₃ + MnO₂ + NO
Title: Re: going in circles when balancing equation
Post by: Alberto_Kravina on May 16, 2006, 01:37:41 PM: Apart from Borek's monster-equations ;) , This is one that I had to balance at school yesterday:

P + KOH + H₂O ? PH₃ + KH₂PO₄