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Author: Subject: Notation
JoeyJoystick
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Notation

Hi All,

I have a question regarding chemical notation. I came across the following in an article regarding the precipitation of iron from various ores.

2FeSO4 + 2H2O + 0.5O2 = Fe2O3 + 2 H2SO4

For what I want to know I have a good enough understanding of this. However, They write '0.5O2'. I am not a chemist but I think I understand the difference between 'O2' and 'O'. (In case I am wrong; with O2 there is a bond between the 2 oxygen atoms and with 2 free floating 'Os' this is not the case. This implies different energy levels between the 2 states) But can someone please explain me the difference between '0.5O2' and 'O'? (Because with the above in my mind. 0.5O2 is still a single O. Well in my mind that is of course. It does however, I think, take energy to go from 'O2' to '2O' And then I am starting to get lost... But at the same time I have a feeling that the answer may have something to do with this.)

Would it have been wrong in this case to write

'2FeSO4 + 2H2O + O = Fe2O3 + 2 H2SO4' (I don't know why, but this just seems to make more sense to me...)

or

'4FeSO4 + 4H2O + O2 = Fe2O3 + 2 H2SO4'?

hmmm, this is one of those times I am afraid I am asking a really stupid question, but it is bugging me so I need to know. lol.

Anyways, thanks in advance for taking the time to explain.

Joey

[Edited on 30-8-2020 by JoeyJoystick]
JoeyJoystick
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Hi All,

And for a full context for those interested or wondering; here a link to the article referenced. https://core.ac.uk/download/pdf/77021587.pdf

Joey
TheMrbunGee
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Hi,

It is half a mol of diatomic oxygen and it cannot be exchanged to a whole mol of atomic oxygen. O and O2 are completely different substances, and are not interchangeable. It helps to indicate count of atoms in molecule by subscript and count of moles by means of normal sized numbers. That way °one can be sure that those numbers states different qualities of reaction.

4 FeSO4 + 4 H2O + O2 = 2 Fe2O3 + 4 H2SO4

or

2 FeSO4 + 2 H2O + 0.5 O2 = Fe2O3 + 2 H2SO4

These are same reactions, 1st being on a twice as large scale. If You change "small" numbers - You have different substances (and if done so, it is a completely different reaction), but changing "large" ones changes scale of reaction, and those must be changed for all molecules in equation or not at all.

Hope it makes sense.

[Edited on 30-8-2020 by TheMrbunGee]

Maurice VD 37
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O and 1/2 O2 are not the same stuff. When speaking of a large number of molecules, 1/2 O2 means half a mole of O2. In the lab, you never oxygen atoms alone. The always get by "groups" of two atoms, by molecules O2. Simple O can never be found in equations.
Tsjerk
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 Quote: Originally posted by Maurice VD 37 Simple O can never be found in equations.

I'm sure AJOEKER begs to differ
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 Quote: Originally posted by Maurice VD 37 O and 1/2 O2 are not the same stuff. When speaking of a large number of molecules, 1/2 O2 means half a mole of O2. In the lab, you never oxygen atoms alone. The always get by "groups" of two atoms, by molecules O2. Simple O can never be found in equations.

Atomic oxygen actually exist. It's unstable radical, often as some unstable intermidiate in reaction. It have better oxidation abilities than normal oxygen. The simplest reaction with atomic oxygen is formation of ozone.

Disociation of O2 by UV light:

O2 --> 2O

And then reaction of O with O2:

O + O2 --> O3

If you are interested in aqueous inorganic chemistry look at https://colourchem.wordpress.com/main-page/

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karlos³
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The one if a half equivalent of the normal diatomic oxygen, the other, one eq. of singlet or monoatomic oxygen, is different.
Just think of triatomic oxygen, ozone, can you compare that with plain O2?
Could you replace the 0,5eq. of diatomic oxygen with 0,33eq. of O3, ozone?
Of course you can not.
So please research this here: https://en.wikipedia.org/wiki/Allotropes_of_oxygen
woelen

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Usually, chemical equations are written with integral (integer) coefficients for the compounds (here the coefficients are the numbers in front of the compounds). Sometimes, however, fractional coefficients are used.

An example is combustion of hydrogen to water:

2 H2 + O2 --> 2 H2O

Here the compounds are H2 and O2 at the left, and H2O at the right.
The coefficients are 2 and 1 at the left, and 2 at the right.

Such chemical equations are fully specified, save a factor. All coefficients may be multiplied with any non-zero factor, e.g.

4 H2 + 2 O2 --> 4 H2O
10 H2 + 5 O2 --> 10 H2O
H2 + ½ O2 --> H2O
½ H2 + ¼ O2 --> ½ H2O

All of the above are equivalent.

Changing the formulas of the compounds is not allowed. That would describe another reaction, or would make the equation nonsensical.

Common practice is to use coefficients, such that they are as small as possible, but still all of them are integral. In this simple example, those coefficients are 2, 1, and 2. Making them smaller requires you to use fractional values. Sometimes people use fractional coefficients, for varying reasons.

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