Chapter 7, Problem 45A

Interpretation Introduction

Interpretation:

A balanced chemical equation corresponding to the decomposition of hydrogen peroxide into oxygen and steam needs to be presented.

Concept Introduction:

• A chemical reaction is expressed as a chemical equation having reactants and products on left and right side of the reaction arrow respectively.

  $\text{Reactants }\to \text{ Products}$

• A balanced chemical equation is one in which the number of atoms of various elements on the reactants side is equal to that on the product side. It depicts the stoichiometry of a given reaction.
• The equations are balanced in two steps:

1) Balance the atoms by matching the number of atoms of each type on the reactants and product side.

2) Adjust the coefficients to the smallest whole number. A coefficient of '1' is implied and therefore not explicitly written.

Answer to Problem 45A

  ${\text{2H}}_{\text{2}}{\text{O}}_2\text{(aq)}\stackrel{{\text{MnO}}_{\text{2}}}{\to }{\text{ 2H}}_{\text{2}}{\text{O (g) + O}}_2\text{(g) }$

Explanation of Solution

The given equation involves the catalytic decomposition of hydrogen peroxide solution into oxygen gas and water vapour. The reactants and products are:

Reactant:

  ${\text{Hydrogen peroxide, aqueous - H}}_{\text{2}}{\text{O}}_2\text{(aq)}$

Products:

  $\begin{array}{l}{\text{Oxygen, gas - O}}_2\text{ (g)}\\ {\text{Water vapor - H}}_{\text{2}}\text{O (g)}\end{array}$

Unbalanced equation:

  ${\text{H}}_{\text{2}}{\text{O}}_2\text{(aq)}\stackrel{{\text{MnO}}_{\text{2}}}{\to }{\text{H}}_{\text{2}}{\text{O (g) + O}}_2\text{(g) }$

The above equation is not balanced since the number of O atoms is 2 on the reactants side and 3 on the products. In order to balance the above equation, multiply both H₂O₂ and H₂O by 2 to get:

  ${\text{2H}}_{\text{2}}{\text{O}}_2\text{(aq)}\stackrel{{\text{MnO}}_{\text{2}}}{\to }{\text{ 2H}}_{\text{2}}{\text{O (g) + O}}_2\text{(g) }$

Conclusion

Therefore, 2 moles of hydrogen peroxide decomposes to form 2 moles of water vapour and 1 mole of oxygen gas.