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A question in a Russian EGE test asks to choose 2 chemicals out of 5 with which Chlorine does not react:

  1. Nitrogen - I checked and it reacts

  2. $\ce{KOH}$ -- reacts

  3. $\ce{O2}$ -- reacts

  4. $\ce{NaBr}$ -- reacts

  5. $\ce{Fe}$ -- reacts

I'm at a loss. Which two should I pick then? Maybe Fe and Nitrogen, because they would be the least likely to react?

Here's the question:

enter image description here

Oscar Lanzi
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CowperKettle
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    Checking unknown reactions on obscure sites might lead you into the dark. Nitrogen and oxygen do not react with chlorine. – Ivan Neretin May 02 '17 at 18:47
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    I would suggest nitrogen and oxygen. – aventurin May 02 '17 at 18:48
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    @IvanNeretin - yes it can, but I could not think of a way to investigate this by other means. There is no authoritative source on "non-reactivity of elements". I thought of oxygen, but then I thought that maybe it does react a bit. – CowperKettle May 02 '17 at 18:52
  • I now can see why Oxygen does not react (they are both oxidants). But why not Nitrogen.. – CowperKettle May 02 '17 at 18:57
  • Chlorine and oxygen react as $\ce{Cl + O2 =ClO + O; 2ClO = ClO2 + Cl}$ as well as $\ce{2Cl + N2 = Cl2 + N2}$ and are described in a famous paper Porter & Wright, Faraday Society Discussions, 1953, No.14, p23 'Studies of the Free Radical Reactivity by the methods of Flash Photolysis: the photochemical reaction between chlorine and oxygen'. – porphyrin May 02 '17 at 20:03
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    @porphyrin You can react everything with everything if you use appropriate conditions. This is dumb test question and if you simply mix Cl2 with air there is no significant reaction. Cowper I have a bad feeling... Tests aren't meant to be solved via digging through internet, but by smart thinking and clever guess – Mithoron May 02 '17 at 20:21
  • @Mithoron - I only started refreshing my chem knowledge on April 21, so I ran out of smart thinking and clever guess pretty fast with this question. – CowperKettle May 03 '17 at 02:57
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    Minor point here. When I read the Russian words for (2) they look like "gidroxid kaliya". How is this sodium hydroxide not potassium (kalium) hydroxide? – Oscar Lanzi Sep 05 '18 at 23:03
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    @OscarLanzi -ooops my mistake! Thanks for spotting it. – CowperKettle Sep 06 '18 at 01:49

2 Answers2

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Chlorine reacts with all of the chemicals except nitrogen and oxygen. We expect elemental nitrogen/oxygen and chlorine to directly combine to form nitrogen trichloride/chlorine oxides but chlorine doesn't have enough energy to break the triple bond of nitrogen and overcome the activation energy of the reaction (also see collision theory). But there has been attempt to get singlet/atomic oxygen react with chlorine. See here and here.

Nilay Ghosh
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    All nitrogen chlorides and chlorine oxides are endothermic. That doesn't preclude a reaction but, especially given there's no huge entropic driver in any case I can think of, it does make it unlikely. The reference given for nitrogen is very strange, and the one for oxygen while correct is poorly worded, or at least titled. – Ian Bush May 03 '17 at 06:49
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Its most likely $\ce{Fe}$ and $\ce{N}$ like you typed. $\ce{N}$ is most accurate because nitrogen is nonreactive so a spark will be needed to react it with chlorine. $\ce{Fe}$ will react with Chlorine but its reactivity is rather low compared to other transition metals such as zinc.

A.K.
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Alexander_the_great
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  • but iron does react with chlorine. It's not about low reactivity but whether it can react at all or not. The answer should be binary(Y/N). – Nilay Ghosh Mar 06 '23 at 05:59