Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: abcc on February 12, 2007, 07:37:56 AM
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what is the difference between electron gain enthalpy & electron affinity??
why EGE is always negative ???
thx
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Electron Gain Enthalpy is the energy transfered when an electron is added to an atom, molecule or ion. It can be exothermic or endothermic. Also called Electron Affinity
Example: A + e- ----> A-
deltaH = electron gain enthalpy and Electron Affinity = -(electron gain enthalpy)
- When deltaH is POSITIVE indicate A- is unstable relative to A
- When deltaH is NEGATIVE indicate A- is more stable than A
To more information go to GOOGLE...
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Electron Gain Enthalpy is the energy transfered when an electron is added to an atom, molecule or ion. It can be exothermic or endothermic. Also called Electron Affinity
Example: A + e- ----> A-
deltaH = electron gain enthalpy and Electron Affinity = -(electron gain enthalpy)
- When deltaH is POSITIVE indicate A- is unstable relative to A
- When deltaH is NEGATIVE indicate A- is more stable than A
To more information go to GOOGLE...
Actually, I still don't understand :'(
As you said that EGE = EA
but why EA= - EGE ???
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Usually, first EA is negative because you are adding an electron, of which feels a greater nuclear charge. This releases energy.
Remember the Bohr model. Going from n=2 to n=1 releases energy. i.e., closer to the nucleus.
These are many-electron atoms, but I'm just using a simple example.
Second EA and higher EAs are positive. Can you estimate why?
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Usually, first EA is negative becaue you are adding an electron, of which feels a greater nuclear charge. This releases energy.
Remember the Bohr model. Going from n=2 to n=1 releases energy. i.e., closer to the nucleus.
These are many-electron atoms, but I'm just using a simple example.
Second EA and higher EAs are positive. Can you estimate why?
ya :)
i know ~
EA is positive because energy is required to counterbalance the repulsion between the incoming e- and the e- that in the atom
but..
so why EA= - electron gain enthalpy ?
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EA, energy, it's all the same. Your units are in enthalpy, my reference just indicates it as energy. At constant pressure, E is H.
You're just stating EA in terms of energy released, which is negative.
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I think he doesn't understand why
EGE is (-1 * EA) or the negative of EA
as written here: "Electron Affinity = -(electron gain enthalpy)"
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I think he doesn't understand why
EGE is (-1 * EA) or the negative of EA
as written here: "Electron Affinity = -(electron gain enthalpy)"
BINGO :)
so , do you know why???
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EGE is still negative, because the energy is flowing towards the surroundings of your system.
You can't say that -EA = -EGE => EA = EGE
Enthalpy and energy are the same thing in this case.
So to say that EA = -EGE is the same thing as saying EA = -E.
Where E is energy.
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EGE is still negative, because the energy is flowing towards the surroundings of your system.
You can't say that -EA = -EGE => EA = EGE
Enthalpy and energy are the same thing in this case.
So to say that EA = -EGE is the same thing as saying EA = -E.
Where E is energy.
is it true that EGE is -ive?
My doctor told me that EA is +ive
so....EA =-EGE
but my question is if EA is the same thing as EGE, so why do they have different sign???
why EA is +ive, but EGE is -ive ???
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I'm sorry I don't understand why EA would be positive in the physical sense.
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I'm sorry I don't understand why EA would be positive in the physical sense.
EA is positive because energy is required to counterbalance the repulsion between the incoming e- and the e- that in the atom
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I'm sorry I don't understand why EA would be positive in the physical sense.
do you think that EA has the same meaning with EGE???
are they the same thing???
as i know, they both mean "adding electron" to atom
so , i think they are the same thing~
but if they are the same, why EA = -EGE, but not EA=EGE
I feel confused
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according to wikipedia,
" It should be noted that the sign convention for electron affinity is the opposite to most thermodynamic quantities: a positive electron affinity indicates that energy is released on going from atom to anion."
Thus, EA is just another way of writing EGE. They are equal in all other respects other than EA is just -EGE -> opposite sign system.
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according to wikipedia,
" It should be noted that the sign convention for electron affinity is the opposite to most thermodynamic quantities: a positive electron affinity indicates that energy is released on going from atom to anion."
Thus, EA is just another way of writing EGE. They are equal in all other respects other than EA is just -EGE -> opposite sign system.
regardness of the sign system?
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yes. If for the reaction
X + e- >X-
delta H is lets say -250kJ /mol,
EGE = -250kJ / mol
EA = -EGE = 250kJ /mol
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yes. If for the reaction
X + e- >X-
delta H is lets say -250kJ /mol,
EGE = -250kJ / mol
EA = -EGE = 250kJ /mol
that means they have the same meaning, but not the same???
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Actually EA is just the delta H of the reaction:
X- > X + e-
According to the IUPAC gold book. So it would be negative of EGE ( delta H when reaction X + e- -> X- takes place) , which is the reaction taking place in the other direction.
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Actually EA is just the delta H of the reaction:
X- > X + e-
According to the IUPAC gold book. So it would be negative of EGE ( delta H when reaction X + e- -> X- takes place) , which is the reaction taking place in the other direction.
??
electron affinity----- X+ e- > X-
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First EA is negative, not positive. I don't trust Wikipedia.
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You should trust the IUPAC gold book then :P
http://goldbook.iupac.org/E01977.html
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You should trust the IUPAC gold book then :P
http://goldbook.iupac.org/E01977.html
Yes, it says it is negative as well:
The equivalent more common definition is the energy released (Einitial-Efinal) when an additional electron is attached to a neutral atom or molecule.
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First EA is negative, not positive. I don't trust Wikipedia.
if EA is -ive,
EGE also is -ive....
then why EA=-EGE ???
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You should trust the IUPAC gold book then :P
http://goldbook.iupac.org/E01977.html
THX FOR the reference ;D
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First EA is negative, not positive. I don't trust Wikipedia.
if EA is -ive,
EGE also is -ive....
then why EA=-EGE ???
The 1st Electron Affinity of an element is the enthalpy change when 1 mole of gaseous atoms of that element each gain an electron to form gaseous ions each with a single negative charge. Often exothermic as the negative electron is attracted to positive nucleus.
Maybe that will help.
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First EA is negative, not positive. I don't trust Wikipedia.
if EA is -ive,
EGE also is -ive....
then why EA=-EGE ???
The 1st Electron Affinity of an element is the enthalpy change when 1 mole of gaseous atoms of that element each gain an electron to form gaseous ions each with a single negative charge. Often exothermic as the negative electron is attracted to positive nucleus.
Maybe that will help.
sooooo
EA is -ive as it is exothemic
then that means EA = EGE ???
BUT SOMEONE said EA = - EGE
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No!
EGE and EA are the same thing. You don't say that because EA is negative, and EGE is negative, then EA = EGE.
EA = -EGE
or
EA = -kJ/mol
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No!
EGE and EA are the same thing. You don't say that because EA is negative, and EGE is negative, then EA = EGE.
EA = -EGE
or
EA = -kJ/mol
???
but if they are the same,
why do they have different 'sign'???
-ive and + ive have different meanings respectively.
give an example: if EA= -165, then EGE = +165( since EA= - EGE)
they have same magnitude and meaning ???
but - ive means energy realeased to surrounding; +ive means energy absorbed .
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You should trust the IUPAC gold book then :P
http://goldbook.iupac.org/E01977.html
Yes, it says it is negative as well:
The equivalent more common definition is the energy released (Einitial-Efinal) when an additional electron is attached to a neutral atom or molecule.
The Einitial is higher than Efinal if energy is released when an additional e- is attached to a neutral atom/molecule, so it should be positive.
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i am still confuseddddd :'(
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I'm not totally sure, but it may be a convention to record EGE as a positive value.
Heat of Hydrogenation, for example, is recorded as a positive enthalpy value even though it is truly negative.
I don't know where you're getting your sources from, but mine records EAs as negative. EGEs may be positive just because it's convention.
If this goldbook says EA is positive, then that is no more wrong than my reference text.