Question

Why is $C{l_2} + KI \to KCl + {I_2}$ not a synthesis reaction?

Answer 1

Synthesis reactions are the one’s which involve two atoms or small compounds combining together to form a large compound. No side products are formed and one single product is obtained always. Let us check if the given reaction satisfies the conditions of a synthesis reaction.

Complete answer:
Synthesis reactions are the ones that occur between two atoms or molecules when they interact to form a molecule or a compound. In most of the synthesis reactions energy is released, meaning the reaction is exothermic. But sometimes the reaction can be endothermic also. The general form a synthesis reaction can be given as:
$A + B \to AB$
The reaction given to us is a single displacement reaction which involves a compound and a molecule which give a compound and a molecule. The single displacement reaction can be given as:
$Element + Compound \to Compound + Element$
Here the more reactive element chlorine, displaces the less reaction element iodine from its salt (KI). Since more than one product is formed, this can be termed as a single displacement reaction. The balanced chemical equation of the given reaction is:
$C{l_2} + 2KI \to 2KCl + {I_2}$ .

Note:
Sometimes the reaction can be more complex than just $A + B \to AB$ . Sometimes more than two molecules and mixtures of products can occur with reactive or intermediates may be formed. Depending on the orientation of collision both the product and the by-product can be formed which may result in less purity of the compound. Synthesis reactions are the major class of the reactions which includes combustion, single displacement, double displacement etc.