# Is this a correct way to write a chain reaction?

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

• We tend not to combine two reactions on the same line. – Ivan Neretin Jun 17 '20 at 9:52
• So, writing them in two separate lines would be more appropriate. Thank You! – Rajdeep Sindhu Jun 17 '20 at 9:57
• 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. – Maurice Jun 17 '20 at 10:36
• 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. – Rajdeep Sindhu Jun 17 '20 at 10:39
• No and no. The term is indeed used in chemistry, but it has a different meaning. en.wikipedia.org/wiki/Chain_reaction – Ivan Neretin Jun 17 '20 at 10:43

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.
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.