Question

Which one is not a chemical decomposition reaction?

• A. $2{NaHCO}_3\to {Na}_2{CO}_3+H_{2}O+{CO}_2$
• B. $Zn+2HCl\to {ZnCl}_2+H_2$
• C. $2{Pb}_3{O}_4\to 6PbO+O_2$
• D. ${CuCO}_2\to CuO+{CO}_2$

Answer 1

The correct option is B

$\mathrm{Zn}+2\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$

Explanation for incorrect answer:

A decomposition reaction is a type of chemical reaction in which a reactant decomposes or breaks down to give one or more than one product.

Example of a decomposition reaction:

• $2{\mathrm{NaHCO}}_3\to {\mathrm{Na}}_2{\mathrm{CO}}_3+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2$
• $2{\mathrm{Pb}}_3{\mathrm{O}}_4\to 6\mathrm{PbO}+{\mathrm{O}}_2$
• ${\mathrm{CuCO}}_2\to \mathrm{CuO}+{\mathrm{CO}}_2$

In these reactions, one reactant is decomposing into more than one product.

Explanation for correct answer:

$\mathrm{Zn}+2\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$

• Displacement reaction: A displacement reaction is a type of chemical reaction in which a more reactive metal displaces a less reactive metal from its salt solution.
• This is a displacement reaction as in this reaction Zinc(Zn) being more reactive replaces hydrogen from hydrochloric acid(HCl).

Here all the choices show decomposition reaction except B.

Hence the correct option is B