Chain reaction is the reaction going in such a way that each subsequent its stage is initiated by the particle which appeared (allocated) as a reaction product at the previous stage. As a rule, as such particles, free radicals act if it is about chemical chain reactions. In cases with nuclear chain reactions, such particles neutrons are. In development of the theory of chain reactions our compatriot Semyonov awarded for it the Nobel Prize made a big contribution. How do chain reactions take place?
Instruction
1. Consider one of types of chain chemical reactions – halogenation of saturated hydrocarbons (alkanes). Take for an example the most plain hydrocarbon – methane. Its formula CH4. How does methane chlorination go?
2. First of all, it is necessary to initiate process. Under the influence of ultra-violet radiation, a molecule breaks upon atomsof chlorine: Cl2 = Cl. + Cl.
3. Atomic chlorine is extremely chemically active, he immediately "attacks" a hydrocarbon molecule, "selecting" at it an electron by means of which completes the electronic level to a steady state. But other radical of CH3 which immediately enters interaction with molecule Cl2, forming a molecule of CH3Cl chlormethane and an atomic radical of Cl is as a result formed. General scheme of this stage: CH4 + Cl2 = CH3Cl + HCl.
4. Respectively, the chlormethane molecule instantly is exposed to "attack" of this atomic chlorine which "selects" an electron at the second atom of hydrogen. Therefore the hydrocarbon radical is again formed. And that reacts with the next molecule of chlorine, and the dichloromethane molecule, or a chloride methylene, and chloride hydrogen turns out: CH3Cl3 + Cl2 = CH2Cl2 + HCl.
5. According to just the same scheme there is the subsequent stage of reaction therefore trichloromethane (chloroform) is formed of dichloromethane (chloride methylene): CHCl3.
6. And the last stage – education from phenoxin chloroform (or tetrachloride carbon) CCl4. Reaction comes to an end when atoms chlorine cannot force out more hydrogen atoms any more, taking their places.