dttom Posted January 20, 2006 Posted January 20, 2006 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?
Ilja Posted January 20, 2006 Posted January 20, 2006 Uve got to calculate , products - edukts = energy that is needed to form this compound 02(gas) has no energy and Na(solid) too , if the energy of Na2O is negative then its exotherm.
woelen Posted January 20, 2006 Posted January 20, 2006 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).
RyanJ Posted January 20, 2006 Posted January 20, 2006 If your interested you can see the reaction for yourself here: http://genchem.chem.wisc.edu/lab/PTL/PTL/Elements/Na/Na_Video.html One I would like too see if Sodium Burning in Hydrogen... Burning in Oxygen is still fun though Cheers, Ryan Jones
YT2095 Posted January 20, 2006 Posted January 20, 2006 Burning in Hydrogen!? LOL, I`de like to see that Myself!
RyanJ Posted January 20, 2006 Posted January 20, 2006 Burning in Hydrogen!? LOL' date=' I`de like to see that Myself! [/quote'] I'd also like to see Francium react with water nut I don't think that will happen either Cheers, Ryan Jones
dttom Posted January 20, 2006 Author Posted January 20, 2006 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?
jdurg Posted January 20, 2006 Posted January 20, 2006 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).
woelen Posted January 20, 2006 Posted January 20, 2006 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.
Ferdinand Posted January 20, 2006 Posted January 20, 2006 I have always had the desire to throw a piece of caesium into water and simultaneously drop some into fluorine gas.
budullewraagh Posted January 21, 2006 Posted January 21, 2006 actually i'd like to see that happen in liquid fluorine. speaking of which, has anyone here seen pics of liquid fluorine? it looks vaguely ominous.
jdurg Posted January 21, 2006 Posted January 21, 2006 I may recall having seen an image of liquid fluorine. If memory serves me right, it was a light yellow in color.
budullewraagh Posted January 21, 2006 Posted January 21, 2006 yeah, pretty much. i also recall it as looking scary
RyanJ Posted January 21, 2006 Posted January 21, 2006 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
woelen Posted January 21, 2006 Posted January 21, 2006 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 . I only make them in small quantities and do not store them.
jdurg Posted January 22, 2006 Posted January 22, 2006 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.
RyanJ Posted January 22, 2006 Posted January 22, 2006 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 Cheers, Ryan Jones
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