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About Na and O2


dttom
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The reaction between Na and O2 as the following:

4Na + O2 --> 2Na2O

Once I check the data base, I found out that the first ionization energy of Na is +500kJ/mol; the first electron affinity of O is -142kJ/mol; the second electron affinity is +850kJ/mol, so if I add up these numbers, the result should be positive, so is that means that the reaction is an endothermic reaction?

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Ionization takes a lot of energy, so that would indeed mean that the reaction is very strongly endothermic. But... you forget about the crystal lattice formation. The combining of O(2-) ions and Na(+) ions gives a lot of energy, so much, that the net reaction is strongly exothermic and that is exactly what we observe. Na metal burns very well (too well, actually).

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Ionization takes a lot of energy, so that would indeed mean that the reaction is very strongly endothermic. But... you forget about the crystal lattice formation. The combining of O(2-) ions and Na(+) ions gives a lot of energy, so much, that the net reaction is strongly exothermic and that is exactly what we observe. Na metal burns very well (too well, actually).

Well, then how to calculate the energy given out during combination?

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I'd also like to see Francium react with water nut I don't think that will happen either :(

 

Cheers' date='

 

Ryan Jones[/quote']

 

 

Heh. Well, first they'd have to go and actually produce enough francium for one to visibly see. ;) Still, I don't think you'd see any difference in reaction between Fr + H2O and Cs + H2O. Both metals would be liquid as the reaction takes place, and both metals would be denser than water. Since the physical properties would be the same, you would not see any difference in reaction violence or speed. As it is, you can BARELY notice a difference between Rb and Cs reacting with water.

 

As for sodium burning in a gas, the burning of sodium in a chlorine gas atmosphere is pretty neat, as is the burning of sodium in a bromine or iodine atmosphere. (Though getting the reaction going in the Br2 or I2 atmosphere is a bit of a PITA).

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Well, then how to calculate the energy given out during combination?

You need to know the lattice energy of Na2O, that is the energy, released when two moles of Na(+) ions and one mole of O(2-) ions (theoretically) are combined to the solid Na2O. This energy is given in kJ/mol. I don'h have this info at hand, but there are tables for lattice energies of many ionic compounds.

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yeah, pretty much. i also recall it as looking scary

 

 

I've never sen it as a liquid nor as a gas except in pictures and it looks pretty wierd when its a gas - its not often you see a pale yellow gas nor a pale green for chlorine either.

 

Its odd that they have such inusual colours...

 

Cheers,

 

Ryan Jones

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I've never sen it as a liquid nor as a gas except in pictures and it looks pretty wierd when its a gas - its not often you see a pale yellow gas nor a pale green for chlorine either.

 

Its odd that they have such inusual colours...

 

Cheers' date='

 

Ryan Jones[/quote']

It is not that strange...

 

I have seen (and made) colored gases or vapors many times. In fact, colored gases are among the things, which really intrigue me. The following I have made at home several times:

 

NO2 : brown

Br2 : red/brown

ONCl : orange

Cl2 : green

ClO2 : deep lime yellow

I2 : purple

IBr : red

 

The only type of colors, I've never seen myself are the bright greens and blues. I know of two blue gasses, but I've not been able to make them:

 

CF3NO

ONCN

 

The latter I tried to make (from NOCl and solid NaCN), but that only yielded black solid crap (probably mostly azulmic acid).

 

Making these colored gases really is fun, but it is not something for the inexperienced home chemist. These gases are either toxic, very toxic or extremely toxic :D . I only make them in small quantities and do not store them.

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yeah, pretty much. i also recall it as looking scary

 

Yeah, I think a lot of that is psychological. We all know that fluorine is INCREDIBLY reactive and toxic, so when we see it our brain kicks in a bit of an alarm. A good analogy is nitroglycerin and vegetable oil. They both have the same yellowish, oily color to it, but when you look at a vial of vegetable oil you don't get nervous. When looking at a vial of nitroglycerin, however, your heart rate goes up a little bit and it "looks" more reactive.

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Yeah, I think a lot of that is psychological. We all know that fluorine is INCREDIBLY reactive and toxic, so when we see it our brain kicks in a bit of an alarm. A good analogy is nitroglycerin and vegetable oil. They both have the same yellowish, oily color to it, but when you look at a vial of vegetable oil you don't get nervous. When looking at a vial of nitroglycerin, however, your heart rate goes up a little bit and it "looks" more reactive.

 

Thats a good point, we have an inbuilt alarm system - Wooo!

 

Making these colored gases really is fun' date=' but it is not something for the inexperienced home chemist. These gases are either toxic, very toxic or extremely toxic . I only make them in small quantities and do not store them.

[/quote']

 

Lots of great choices there.... All douns like they should be avioided like a plague if you ask me :D

 

Cheers,

 

Ryan Jones

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