Question

Which of these chemical equations is not balanced?

• A. $2\text{Mg (s)}+{\text{O}}_2\text{(g)}\to 2\text{MgO (s)}$
• B. ${\text{CO}}_2\text{(g)}+6{\text{H}}_2\text{O (l)}\to {\text{C}}_6{\text{H}}_{12}{\text{O}}_6\text{(s)}+6{\text{O}}_2\text{(g)}$
• C. ${\text{CuCl}}_2\text{(aq)}+{\text{Pb (NO}}_3{)}_2\text{(aq)}\to {\text{Cu(NO}}_3{)}_2\text{(aq)}+{\text{PbCl}}_2\text{(g)}$
• D. ${\text{CaCO}}_3\text{(s)}\to \text{CaO (s)}+{\text{CO}}_2\text{(g)}$

Answer 1

The correct option is B

${\text{CO}}_2\text{(g)}+6{\text{H}}_2\text{O (l)}\to {\text{C}}_6{\text{H}}_{12}{\text{O}}_6\text{(s)}+6{\text{O}}_2\text{(g)}$

In an unbalanced chemical equation, the number of atoms of each element on either side of the arrow i.e. on the reactant and product side is not equal.
If you count the number of atoms for equations given in options then we have the equal number atoms of each element on reactant and product side except for one reaction. We don't have the equal number of atoms on the reactant and product side for the reaction given below:

${\text{CO}}_2\text{(g)}+6{\text{H}}_2\text{O (l)}\to {\text{C}}_6{\text{H}}_{12}{\text{O}}_6\text{(s)}+6{\text{O}}_2\text{(g)}$

Clearly, number of carbon and oxygen atoms on the reactant side is not equal to that in the product side.
The balanced chemical equation would be:

$6{\text{CO}}_2\text{(g)}+6{\text{H}}_2\text{O (l)}\to {\text{C}}_6{\text{H}}_{12}{\text{O}}_6\text{(s)}+6{\text{O}}_2\text{(g)}$