Talk:Stoichiometry

Old discussion

Why does the Stoichiometric air-fuel ratios of common fuels section need to be in here? It seems random and out of place. 129.118.97.125 (talk) 21:19, 21 January 2009 (UTC)

This article has used different markup styles:

2H₂ + O₂ --> 2H₂O

2H₂ + O₂ --> 2H₂O

Both styles are typographically inadequate. I tried to fix the right arrow with → with the following result:

2H₂ + O₂ → H₂O

which isn't rendered quite right in my browser (IE 6.0)—the arrow is on the baseline instead of "hyphen height". (The problem seems to be that the arrow is centered vertically on the whole line, which is pulled down by the subscripts. For example, H→O does look right.) Finally, I have decided to switch to TeX markup

$2\,{\mbox{H}}_{2}+{\mbox{O}}_{2}\to 2\,{\mbox{H}}_{2}{\mbox{O}}$

in the hope that this satisfies everybody.
—Herbee 21:31, 2004 Mar 3 (UTC)

I love how the formula for thermite is on this page. Mayhaps an explosive should not be used as an example. miles32

It is explosive. :) Other reactions common in textbooks, such as H2 + O2 -> H2O are more likely to be explosive. Itub 02:27, 16 January 2007 (UTC)

Should there be H2 + O2 -> H2O + O2 Giving the other product O2?

Nah the balanced equation is 2H2 + O2 -> 2H2O. Bsimmons666 (talk) 19:03, 18 October 2008 (UTC)

Merger proposal

All these articles (Stoichiometry,Stoichiometric coefficient,Gas stoichiometry)are related to the same concept and would be better if they are accessible on a single page. It will help by providing a better understanding of the article and save some trouble for a person new to the concept. Myth (Talk) 21:00, 28 January 2007 (UTC)

I Believe that the links included in the See Also section should be enough... both subjects are prone to grow up enough to keep their own pages... —Preceding unsigned comment added by Paulo.maia (talk • contribs) 06:57, 26 March 2007

they should go together. 'nuff said. —Preceding unsigned comment added by 67.84.0.201 (talk)

They should be merged until it is true that they have grown and developed enough information to merit their own space in separate articles. --Antonio.sierra 01:32, 6 September 2007 (UTC)

Added a short section on the stoichiometry matrix. --hsauro 08 Oct 2007

Counting

I might just suck at counting, but I believe in "Different stoichiometries in competing reactions" there is an extra Hydrogen. Well actually it's an extra n hydrogens, but I think people get it... WAIT!!! that does say 6-n... hm... LIMEY 07:09, 2 December 2007 (UTC)

Addition

This article needs to mention something about Job's method. —Preceding unsigned comment added by 204.8.12.66 (talk) 15:16, 9 January 2008 (UTC)

In the section Stoichiometric Air/Fuel Ratios of Common Fuels, the mass percent numbers have been calculated incorrectly. For example, for ethanol, the mass ratio is given as 9 to 1 and the mass percent as .11111 which is 1/9. The total mass for this case should be 9+1=10, and then the percent fuel is 1/10 = 10%. This error is consistent for all the fuels. Jpittot (talk) 20:21, 30 January 2008 (UTC)

Is this correct?

The article says, "the units of grams form a multiplicative identity, which is equivalent to one (g/g=1), with the resulting amount of moles (the unit that was needed), is shown in the following equation,

$\left({\frac {2.00{\mbox{ g NaCl}}}{1}}\right)\left({\frac {1{\mbox{ mol NaCl}}}{58.44{\mbox{ g NaCl}}}}\right)=0.034\ mol$"

however it leaves out the NaCl at the end. Shouldn't it be still there as there are two "NaCl" in the numerator while there is one "NaCl"in the denominator,

$\left({\frac {2.00{\mbox{ g NaCl}}}{1}}\right)\left({\frac {1{\mbox{ mol NaCl}}}{58.44{\mbox{ g NaCl}}}}\right)=0.034\ mol{\mbox{ NaCl}}$

(Unless, of course, that italicized "mol" means you don't have to, i dunno...)Electric durian (talk) 07:10, 20 September 2008 (UTC)

Where is composition stoichiometry?

Stoichiometry (sometimes called reaction stoichiometry to distinguish it from composition stoichiometry

Well now then shouldn't "composition stoichiometry" have a page or at least some definition. —Preceding unsigned comment added by 134.131.125.50 (talk) 21:36, 22 October 2008 (UTC)

Agree Logan _Talk ^{Contributions} 23:13, 3 February 2010 (UTC)

Explain the practical side

The article is too centered on the theoretical calculations, which makes it difficult to understand to someone not previously knowing the subject. It should also explain how the experiments are performed and how the "amount of products that can be produced" is measured in practice (not just as the result of a previously defined formula). That is, explain the basis of the technique instead of only the way it's used. Diego (talk) 15:26, 5 January 2010 (UTC)

OH YES IT IS!!!! —Preceding unsigned comment added by 75.23.222.214 (talk) 00:44, 15 January 2010 (UTC)

Non-technical intro

I've rewritten the intro to make it less technical and hopefully less daunting for the non-technical reader. Almost all the original text from the previous version has been kept, but I've rearranged it to bring the example forward and improve the flow of ideas. Also, I've explicitly defined both reaction and composition stoichiometry, as the wiki link in the previous version to composition stoichiometry didn't work (a page on composition stoichiometry may never have existed).

Chemists, help me out here! I'm hoping with a bit more work, we can get rid of the "too technical" tag that has been placed on the article. Pls review the examples and definitions for accuracy. Also needed are some definitional references to good chemistry textbooks for the various terms defined (I don't have access to any chem textbooks at the moment, and most of the web-based definitions aren't from clearly authoritative sources). Ross Fraser (talk) 00:29, 19 July 2010 (UTC)

Error of sign

In the section defining the stoichiometric coefficient, there are sign errors. "CH4 + 2 O2 → CO2 + 2 H2O, the stoichiometric coefficient of CH4 would be 1 and the stoichiometric coefficient of O2 would be 2."

According to the definition of the "stoichiometric number" by IUPAC, the sign (consumption or production) is included in the coefficient. So in the example the stoichiometric coefficient of CH4 would be -1 and the stoichiometric coefficient of O2 would be -2. http://www.iupac.org/goldbook/S06025.pdf Nicolas Le Novere (talk) 16:19, 17 September 2010 (UTC)

I agree that this needs revision, but see below. KeeYou Flib (talk) 13:33, 19 April 2021 (UTC)

dimensionless

The paragraph starting with "The (dimensionless) "units" may be taken to be molecules or moles. " does not make sense. Stoichiometric numbers are dimensionless because in the current interpretation of reaction kinetics, they represent the substance consumed/produced relative to an hypothetical substance which stoichiometric number would be 1. Another way of saying that is they represent the number of moles/molecules transformed per number of moles/molecules of reaction events. Because it is mole/mole or molecule/molecule, the result is dimensionless. It may not be taken as to be anything. dimensionless is dimensionless. We are talking of the dimensions of the SI units here. mole/mole = second/second = meter/meter = kg/kg. Nicolas Le Novere (talk) 16:19, 17 September 2010 (UTC)

What happened to the 'Definition' section?

In earlier versions there was a section called Definition, that elaborated on the basic concepts. Was it deliberately removed or did it get lost in the wiki cut-n-paste process? I'm restating it into the article, since it seems to have been lost to vandalism. Diego Moya (talk) 13:23, 30 October 2010 (UTC)

Error in Stoichiometric Air Fuel Ratios

There is an error in the mass ratio of air/natural gas for stoichiometric combustion. The ratio is listed as 14.5. Since NG is mostly methane, the ratio should be closer to 17.2 (the correct methane/air mass ratio). Since the table does not give the exact composition of (for example) NG or gasoline, and both of these substances have variable composition, it would be better to cite the NG and gasoline composition for which these ratios are stated. 71.136.237.55 (talk) 20:31, 4 July 2011 (UTC)

The "main reaction" of the combustion of gasoline (petrol) is not C + O2.
Gasoline is not pure carbon!! Is it best to simplify and represent it as 100% octane ? So:
2 C
₈H
₁₈ + 25 O
₂ → 16 CO
₂ + 18 H
₂O
79.78.60.213 (talk) [5 July 2018]

You have a valid point. Gasoline is a complex mixture, but C₈H₁₈ is certainly a more representative formula than C so I have now changed it. And for the same reason, I have changed Diesel from C to C₁₂H₂₆. Dirac66 (talk) 23:24, 10 July 2018 (UTC)

Composition Stoichiometry example in intro makes no sense

"1 mol of ammonia consists of 1 mol of nitrogen and 3 mol of hydrogen. As the nitrogen atom is about 14 times heavier than the hydrogen atom, the mass ratio is 14:3, thus 1 kg of ammonia contains 176 g of hydrogen." -- this makes no sense: it would only be true of 1 mol of ammonia consisted of 1 mol of nitrogen and 1 mol of hydrogen. But there are *3* mols of hydrogen! Unless someone can explain otherwise, I'll re-write this example. --Ross Fraser (talk) 00:34, 21 March 2012 (UTC)

Please don't make corrections based on your personal knowledge, unless you've actually studied chemistry, let alone stoichiometry at this elementary level. The example was referring to the Haber process, and funnily enough it was also wrong, as well as your correction. 1 mol of nitrogen and 3 mol of hydrogen result in 2 mol of ammonia. Remember that hydrogen and nitrogen are also diatomic. Rifasj123 (talk) 06:08, 25 September 2013 (UTC)

Stoichiometry matrix extension to nuclear transformations

How is the stoichiometry matrix extended when nuclear transformations (alpha and beta-decay, nuclear reactions, etc) must be considered? It would be useful to add some details.--188.26.22.131 (talk) 11:04, 26 August 2013 (UTC)

Poor quality

To be honest the quality of this article is abysmal. Its scope is at a high school level, and it seems more suited as a tutorial rather than an encyclopedic page.

If I have time I will make major changes, but hopefully someone with a high degree of knowledge in Chemistry can help improve this article. It only explains topics in the context of solving elementary chemistry problems, and doesn't really elaborate on their interrelation, and relevance to the field of stoichiometry itself. Additionally a historical component could also be beneficial.

But in my opinion the most appalling issue with this article is the lack of citations, and thereby credibility on the subject matter. Rifasj123 (talk) 02:52, 24 September 2013 (UTC)

Wrong volumetric AFR for diesel

All other values in the table are given as air-to-fuel (AFR) volume ratios. If this is also the volumetric-AFR for diesel is clearly wrong. Probably that this is the fuel-to-air volumetric ratio instead - but i wouldn't like to assume. Either way, the table is confusing without explicit headings. — Preceding unsigned comment added by 85.211.37.96 (talk) 11:04, 5 January 2014 (UTC)

Yes, 0.094 volumes (or moles) of air for 1 volume (or mole) of diesel is absurd. The revision history of this article shows that the value 0.094:1 was not in the initial table, but was added on 16 Nov 2009 by editor 71.112.167.243 who has not contributed subsequently. Since we cannot contact him/her to check the source, I will just remove the incorrect value.

As for the headings, the article section in November 2009 had a more explicit title including the words air-to-fuel. I will restore this title to make it clear that the whole table refers to air-to-fuel ratios (except possibly the 0.094). Dirac66 (talk) 14:33, 5 January 2014 (UTC)

Use the word "amount"

The mole is defined as "the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12".

Bearing that in mind, I suggest the ghastly phrase "number of moles" be replaced by the simpler, more accurate word "amount". Thus "the number of moles of methane is 2" becomes "the amount of methane is 2mol". You'd never say "the number of kilograms of potatoes I want is 1", now, would you? Come on - be honest! 90.220.32.65 (talk) 14:16, 14 October 2014 (UTC) Watchkeeper, 14/10/14

Yes, I agree with you, so I have now found and changed 3 occurrences of "number of moles". Dirac66 (talk) 22:49, 14 October 2014 (UTC)

References

Referring to the potato example, one would also never say "amount of kilograms" because a kilogram doesn't represent a number of things. As we all know a mole is just a convenient unit to express a large number of something. I can have a mole of books, but I wouldn't say I have "an amount of books", instead, I would use "a number of books". I can see however that IUPAC uses "amount of moles". Out of curiosity, I noted that Google comes up with 1.5 million references to "amount of moles" and 3.1 million references to "number of moles". Personally I've never used "amount of moles" in my professional work. I'll ask one of my chemistry colleagues who has written a number of well-known chemistry/biochemistry textbooks to see what he thinks. Rhodydog (talk) 01:39, 21 January 2021 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Stoichiometry/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

In the table under "Stoichiometric air-fuel ratios of common fuels", aren't the percentage calculated incorrectly? Eg, Gasoline, ratio of 14.7:1 by weight. The articles states 6.8% fuel by weight, but the total weight would be 15.7 and that makes it 1/15.7 = 6.379% ~ 6.4%. Likewise with the other values.

Last edited at 21:51, 24 September 2008 (UTC). Substituted at 07:06, 30 April 2016 (UTC)

The example reactions in the "Stoichiometry matrix" section need improvement

Since the example contains 3 reactions that make no transformations, S1 and S2 are the same, and S3, S4, and S5 are the same. A better example that shows more distinct species would be easy to write. — Preceding unsigned comment added by Arthur.Goldberg (talk • contribs) 00:20, 19 November 2020 (UTC)

Could you clarify what you mean that S1 and S2 are the same? The transformation S1 -> S2 could be an isomerization so S1 and S2 would be chemically different, there are many such examples. If you have an alternative example I'd be interested to see it. The main thing is that the example should illustrate the cancelation of stoichiometries as in the second reaction, other than that one can be flexible. Rhodydog (talk) 01:21, 21 January 2021 (UTC)

Stoichiometric number definition does not agree with the IUPAC Gold Book source cited or with common usage

The article has a very serious notation problem that also seems to have infected other articles on Wikipedia, so before I start changing things I'd like to ask for consensus.

According to the IUPAC Gold Book: "A chemical reaction of known stoichiometry can be written in general as:

aA+bB+...→...+yY+zZ

For the reaction products Y and Z the numbers y and z are known as the stoichiometric numbers, νY and νZ, for Y and Z respectively. For the reactants the stoichiometric numbers are the negatives of the numbers appearing in the equation; for example the stoichiometric number νA for the reactant A is −a. In other words, the stoichiometric numbers are positive for products and negative for reactants." The Gold Book reflects common usage here, and this notation is used in textbook treatments of chemical thermodynamics in the fields of chemistry and chemical engineering.

However, the article incorrectly refers to the stoichiometric coefficients s_i (which are a, b...,y,z in the example above) as being equal to the stoichiometric numbers $\nu _{i}$ (which are -a, -b ..., y, z). This is important in the theory of chemical thermodynamics and provides the correct pathway for the statement that the change in the number of moles of any species is proportional to the extent of reaction, with coefficient $\nu _{i}$. Anyone mind if I fix this? KeeYou Flib (talk) 13:29, 19 April 2021 (UTC)

I should have mentioned that the problem is specifically in the section entitled "Stoichiometric coefficient". The first introduction of the stoichiometric coeffiecient concept at the top of the page is correct as is. KeeYou Flib (talk) 13:37, 19 April 2021 (UTC)

Since no one raised an objection here, I did my best to boldly fix the problem. KeeYou Flib (talk) 04:28, 5 May 2021 (UTC)

Target of Stoichiometric coefficient redirect

I believe that the concept of stoichiometric coefficient is most easily and visually explained in the context of chemical equation, so I have retargetted it there. Petr Matas 08:37, 27 June 2022 (UTC)

over/under

Is there a definition for over-stoichiometric vs. under-stoichiometric? This came up in another article, which some suspect is the wrong way. It would seem that the definition would depend on which one you are considering first. That is, A reacts with B, is different from B reacts with A, but should be the same. Gah4 (talk) 09:32, 7 December 2022 (UTC)

Continuing the question, when one writes a stoichiometric ratio, is there a convention for which comes first and which second? Gah4 (talk) 09:38, 7 December 2022 (UTC)

Any thoughts on this one? Gah4 (talk) 00:50, 15 December 2022 (UTC)

OK, the actual question is for Diesel exhaust fluid. In the case of gasoline engines, it is lean vs. rich. Also, I am pretty sure it isn't a single word, so changed the question above. Gah4 (talk) 00:56, 15 December 2022 (UTC)

Although this isn't the article in question, I guess it's okay to gather opinions and information here, at least according to WP:APPNOTE. Anyway, I did stumble across these notes - are they perhaps helpful? http://fluid.wme.pwr.wroc.pl/~spalanie/dydaktyka/combustion_MiBM/fund/Stoichiometry.pdf Qflib, aka KeeYou Flib (talk) 22:08, 15 December 2022 (UTC)

Not perfect, but it does help. That leaves the question that does go to this page, about how ratios work. Gah4 (talk) 00:36, 17 December 2022 (UTC)

Tbh, I'm not following. Sorry to be slow. Are you suggesting that the page be changed in some way? If so, in what way specifically? Qflib, aka KeeYou Flib (talk) 19:24, 18 December 2022 (UTC)

The page (only one place) says overstoichiometric. First, I suspect it isn't a word, and should be two words, probably hyphenated. But also, I suspect that the article should explain the meaning in terms of stoichiometric ratios. Or maybe the other way around. That is, if I see an equation, and the term over-stoichiometric, do I immediately know what it means? Gah4 (talk) 00:29, 19 December 2022 (UTC)

Although I agree that clarification is needed for the term, it does seem to be a concept that is in common usage. See here: https://glosbe.com/en/en/overstoichiometric . I think that the concept comes into play when discussing combustion specifically, see here: https://sagemetering.com/combustion-efficiency/stoichiometric-combustion-and-its-impact-on-boiler-efficiency/#:~:text=Stoichiometric%20combustion%20is%20a%20theoretical%20position%20where%20the%20optimal%20amount,reality%2C%20it%20does%20not%20exist. The term understoichiometric seems to come Into play when describing nonstoichiometric compounds with lower-than-stoichiometric ratios of elements such as oxygen. Qflib, aka KeeYou Flib (talk) 03:50, 19 December 2022 (UTC)

Ok, specifically, I was trying to figure out over or under. So, it is over or under for the more electronegative side? The oxidizing part that is often oxygen? In the case of many engines, it is lean and rich, and most know which is which. Most often for oxidation reactions, the oxidizing part is to the right. That is, A + B --> C + D, the B and D are the oxidizing agents, while A and C are the reducing agents. Gah4 (talk) 11:28, 19 December 2022 (UTC)

I don’t think that there’s any strict convention for writing redox reactions in any particular order. If there is, I’ve been doing it wrong for thirty years, so I hope not. Anyway, reading between the lines it seems to me that the concept is specifically used by engineers when they are working with real-world combustion engines and combustion cells, and probably refers to the lean/rich situation. It’s not something that I use as a chemist, that’s for certain. We tend to focus on whether or not a given reagent is the limiting reagent for purposes of synthetic conversion. Qflib, aka KeeYou Flib (talk) 17:34, 19 December 2022 (UTC)

Redundancy in Definition

The Definition section mentions these requirements:

1) All of the reagent is consumed
2) There is no deficiency of the reagent
3) There is no excess of the reagent.

3 seems like a repetition of 1. Matthyis (talk) 18:32, 13 October 2024 (UTC)