CHRIS25
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The nomenclature used to represent Redox
Ok, so I anticipate shaking heads and TchTch at my childish perspective. But in a very serious attempt to understand the logic of the original
concept I want to ask a serious question. The arrow sign and the + and - sign have universal meaning that are well understood. But for me, these
signs need re-interpreting in Redox half equations. Allow me to demonstrate:
In the reaction between silver nitrate and copper, a simple displacement that I have performed, the half reactions are written thus:
Cu0 = Cu2+ + 2e- Oxidation
Ag+1 + e- = Ag0 Reduction
Looking at the above is like reading japanese in a mirror whilst on a roller coaster.
Why was the half equation never written in a way to retain the logical pattern of symbols our brains are accustomed to comprehending?
Cu0 - 2e- = Cu2+
meaning the logical "Cu MINUS 2 electrons PRODUCES Cu2+
and
Ag+1 + ee- = Ag0
meaning the logical "Ag+1 PLUS/AND e- PRODUCES Ag0
Hey just a question I would have asked if I were in a classroom?
PS No I am not bored, just frustrated at having to re-adjust that + can mean minus and the left hand side can mean something that happens on the right
hand side.
[Edited on 3-5-2014 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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Etaoin Shrdlu
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Because reactions are written based on what actually "exists" on both sides. "Negative" amounts of something can't exist. Hence, you write that first
you have an atom of elemental copper, then you have a copper atom in a +2 oxidation state and 2 electrons that no longer belong to that
copper atom, rather than saying that first you have an atom of elemental copper and two nonexistent "negative" electrons, then you have a
copper atom in the +2 oxidation state.
Technically they're both valid ways to look at things, but the first is a closer representation of reality. Does that make sense?
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CHRIS25
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So one is saying, as far as the silver is concerned, that we have a Silver atom with a plus one charge and one electron that does not belong to that
silver atom?
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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Etaoin Shrdlu
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Yes. That electron would belong to another reactant that isn't shown because you're writing half-reactions.
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CHRIS25
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Well I have some brain management to do here, it's like writing the word 'BLUE' in the colour red. You've seen that psychology exercise? At least I
thank you for injecting 'some' logic into this for me. So what, if I dare ask, is the whole purpose of writing half reactions anyway? I failed
Blogfasts exam, but I have done quite a few exercises in redox equations and have added charges and identified oxidants and reduction species and
re-assigned charges. Then I look at the half reactions for these and am absolutely baffled as to their purpose. They tell me nothing that I already
don't know. Unless i am doing all the wrong reaction exercises...
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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CHRIS25
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I just spent 30 minutes following a really good explanation of a half reaction. everything was understood until the last minute where he threw me off
course with something. Anyway, what I ended up seeing (despite not understanding something he did) was Exactly what I had done in 2 minutes without
writing out the half reactions. So my question remains, apart from the intellectual exercise in this, what use does it have, what does it attempt to
show other than what I get from simply transferring charges and identifying oxidation and reduction within my single lined equation. I typed in
google: "what purpose half reaction" - nothing new. The only thing I am frustrated about is the fact that I understand everything that is going on
within an equation/balanced reaction, but when they start breaking it down and using backward meaning terminology, it just gets so infuriatingly
confusing and the whole plot is lost. The seven rules for balancing a redox reaction into half reactions are easy enough to follow, but if you already
know that say Mg is losing one electron on the left side and K is gaining one electron say on the right, what is the senseless point of spending 5
extra minutes confirming this? Throw the book at me I really don't care, but I am being honest, I want to learn but I am spending so much time
understanding the backwards symbolism that is employed that, IF this is important to understand, then I obviously need to get to grips with it. Sorry
for the outlet, Thankyou.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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Etaoin Shrdlu
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I think half-reactions are really just to visualize what the electrons are doing in a reaction. Like exercises in a lot of disciplines, if you
understand what's going on there's really no need to go through with them (one could say you're writing them in your head instead).
They can be used to balance redox equations, but I have never run into a situation where I had to use half-reactions. Even "difficult to balance
without half-reactions" examples are only "difficult" because solvent (usually water) and acidity/basicity need to be taken into account, and those
things won't be written as reactants or products, they'll be around the equilibrium arrow or written in the description of conditions so sometimes
people overlook them. Textbooks often hedge around this point trying to trick you instead of being straightforward. If you don't overlook them I don't
see how a problem would ever arise from just balancing normally to conserve charge and number of atoms.
There may be useful calculations you can do with half-reactions. I don't know enough to say. It would be nice to hear someone else's input on
this as I'm almost only involved with organic chemistry and while there are redox reactions there I have never seen it even suggested that
half-reactions should be written. This implies that they're not necessary for ionic reactions either.
[Edited on 5-4-2014 by Etaoin Shrdlu]
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DraconicAcid
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There are a lot of reactions that are much easier to balance using half reactions. Try dimethylhydrazine
((CH3)2NNH2) with nitric acid to give carbon dioxide, water and nitrogen gas. It's easy with half-reactions; without
half-reactions, it took me half an hour, and my colleagues generally gave up without succeeding.
They're also useful when you're calculating Eo for a reaction. It's much easier to use the tabulated reduction potentials than to work
from Gibb's free energy.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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CHRIS25
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Ok Look, I really appreciate you not ticking me off, was afraid of this. A relief that I am not really missing anything at this stage in my learning,
really. So thanks folks for being patient and taking the trouble to write back. (at a later date I will come back to them maybe).
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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Etaoin Shrdlu
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Does this reaction take place under an inert atmosphere? If not isn't the reason for the trouble that it's a complete combustion reaction, not enough
oxygen coming from the nitric acid to balance the equation, and oxygen gas wasn't taken into account?
2(CH3)2NNH2 + 4HNO3 + 3O2 --> 4CO2 + 10H2O + 4N2
If it is under an inert atmosphere I would be curious to see your solution as these products look mathematically impossible without adding
oxygen. (It's been a long day, hit me over the head with a book if I missed something.)
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IrC
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http://amazingrust.com/Experiments/background_knowledge/Redo...
This page will aid in understanding the subject.
"Science is the belief in the ignorance of the experts" Richard Feynman
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DraconicAcid
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Quote: Originally posted by Etaoin Shrdlu  |
Does this reaction take place under an inert atmosphere? If not isn't the reason for the trouble that it's a complete combustion reaction, not enough
oxygen coming from the nitric acid to balance the equation, and oxygen gas wasn't taken into account?
2(CH3)2NNH2 + 4HNO3 + 3O2 --> 4CO2 + 10H2O + 4N2
If it is under an inert atmosphere I would be curious to see your solution as these products look mathematically impossible without adding
oxygen. (It's been a long day, hit me over the head with a book if I missed something.) |
Try it again, without adding oxygen as a reactant (this would be a liquid-fueled rocket propulsion reaction, so the reaction occurs too quickly for
atmospheric oxygen to get in). Like I said, if you do it by the half-reaction method, it's fairly straightforward.
[Edited on 4-5-2014 by DraconicAcid]
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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CHRIS25
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Thanks I saw this page months ago, it is a good explanation. I actually formed a new thing other than oil and rig
Mine is actually NOILORS AND PRIGOLS I find this helps me to make sense of everything.
NOILORS = more Negative Oxidation is Loss On Right Side
PRIGOLS = more Positive Reduction is Gain On Left Side
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
Etaoin Shrdlu
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| Quote: Originally posted by DraconicAcid | | Try it again, without adding oxygen as a reactant (this would be a liquid-fueled rocket propulsion reaction, so the reaction occurs too quickly for
atmospheric oxygen to get in). Like I said, if you do it by the half-reaction method, it's fairly straightforward. |
If you do it without the half-reaction method it's also straightforward, pure algebra. I had a relationship wrong. -facepalm-
5C2H8N2 + 16HNO3 --> 10CO2 + 28H2O + 13N2
(I didn't half-ass it in my head this time.)
Admittedly half-reactions may be much easier on paper. I confess I don't even know what they would be for that reaction.
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