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I don't know much about chain reactions and how I understand them, they are just a series of chemical reactions where the products of the preceding reaction act as the reactants for the succeeding reactions.

Now, let's assume that $\ce{A}$ and $\ce{B}$ are two compounds that chemically react under certain conditions to give $\ce{X}$ and $\ce{Y}$. This chemical reaction can be written as:

$$\ce{A + B -> X + Y}$$

Now, let's also assume that $\ce{X}$ and $\ce{Y}$ react under the very same conditions to give $\ce{M}$ and $\ce{N}$. This chemical reaction can be written as:

$$\ce{X + Y -> M + N}$$

Now, can the series of these reactions be written as follows : $$\ce{A + B -> X + Y -> M + N}$$

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    $\begingroup$ We tend not to combine two reactions on the same line. $\endgroup$ – Ivan Neretin Jun 17 '20 at 9:52
  • $\begingroup$ So, writing them in two separate lines would be more appropriate. Thank You! $\endgroup$ – Rajdeep Sindhu Jun 17 '20 at 9:57
  • $\begingroup$ Your mechanism is not a chain reaction. An example of a chain reaction may be the radioactive decay chain, like U-238 -> Th-234 -> Pa-234 -> U-234 -> etc. $\endgroup$ – Maurice Jun 17 '20 at 10:36
  • $\begingroup$ Is chain reaction a term specific to nuclear reactions? I assumed that any reaction whose products react to form another set of products without any external conditions would be called a chain reaction. $\endgroup$ – Rajdeep Sindhu Jun 17 '20 at 10:39
  • $\begingroup$ No and no. The term is indeed used in chemistry, but it has a different meaning. en.wikipedia.org/wiki/Chain_reaction $\endgroup$ – Ivan Neretin Jun 17 '20 at 10:43
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Your scheme is one of sequential reactions. The chain reaction has feedback so that one to two reactions occur repeatedly until the reactants are all consumed.

The general scheme is shown in the diagram where $R\cdot$ represents any radical species ( H or Cl in Maurice's answer) and $\alpha$ has to be at least 1 for species $R\cdot$ to continue the chain reaction.

scheme

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  • $\begingroup$ Thanks, that was quite helpful. $\endgroup$ – Rajdeep Sindhu Jun 19 '20 at 5:37
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A good example of chain rection is the photochloration of $\ce{H_2}$ by $\ce{Cl_2}$. The first reaction is due to the first photon striking a chlorine molecule, producing two chlorine atoms Cl. Then each Cl atom reacts with a $\ce{H_2}$ molecule producing one HCl and one H atom. This H atom reacts with another $\ce{Cl_2}$ producing one HCl and a new Cl atom that repeats the first reaction with $\ce{H_2}$ $$\ce{Cl_2 -> 2 Cl}$$$$\ce{Cl + H_2 -> HCl + H}$$$$\ce{H + Cl_2 -> HCl + Cl}$$ And the wole process repeats in a so-called chain reaction, up to the destruction of all reagents. The terminal reaction is $$\ce{H + Cl + M -> HCl + M}$$ and M may be any molecule or substance. The chain reaction is maintained by the production and destruction of H and Cl free atoms.

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