Question

Write the balanced chemical equation for the following:

Zinc and hydrochloric acid react to give zinc chloride and hydrogen gas.

Answer 1

The equation in which the number of atoms of all the molecules is equal on both sides of the equation is termed a balanced chemical equation.

Balancing of a chemical equation by hit and trial method:

Step: 1: Representation of chemical reaction:

$$\begin{gathered} \mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{HCl}\left(\mathrm{l}\right)\to {\mathrm{ZnCl}}_2\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \mathrm{Zinc}\mathrm{Hydrochloric}\mathrm{Zinc}\mathrm{Hydrogen} \\ \mathrm{acid}\mathrm{chloride} \end{gathered}$$

Step: 2: Calculating the number of atoms on both sides of the reaction.

Elements	Number of atoms on the reactant side	Number of atoms on the product side
Zn	1	1
H	1	2
Cl	1	2

Step: 3: Balancing uneven numbers of atoms on the reactants and product side:

• We can see that zinc is already balanced.
• To balance hydrogen and chlorine on both sides of the reaction, we will add 2 against $\mathrm{HCl}$ on reactant side.

$\underset{\mathrm{Zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}\mathrm{chloride}}{2\mathrm{HCl}\left(\mathrm{l}\right)}\to \underset{\mathrm{Zinc}\mathrm{chloride}}{{\mathrm{ZnCl}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}\mathrm{gas}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

Elements	Number of atoms on the reactant side	Number of atoms on the product side
Zn	1	1
H	2	2
Cl	2	2

As the number of atoms on both sides is equal, the equation is balanced.

$\underset{\mathrm{Zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}\mathrm{chloride}}{2\mathrm{HCl}\left(\mathrm{l}\right)}\to \underset{\mathrm{Zinc}\mathrm{chloride}}{{\mathrm{ZnCl}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}\mathrm{gas}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$