Chapter 11, Problem 1STP

Interpretation Introduction

Interpretation: The coefficient of ${\text{H}}_{\text{2}}$ after balancing reaction, ${\text{Fe}}_{\text{2}}{\text{O}}_3{\text{ + H}}_{\text{2}}\to {\text{ Fe + H}}_{\text{2}}\text{O}$ should be identified.

Concept Introduction: A chemical reaction is said to be balanced when the number of atoms for each element in the equation is the same on both sides, that is reactants and products.

Answer to Problem 1STP

Correct answer: option (B) 3.

Explanation of Solution

Reason for correct option:

The given chemical reaction is, ${\text{Fe}}_{\text{2}}{\text{O}}_3{\text{ + H}}_{\text{2}}\to {\text{ Fe + H}}_{\text{2}}\text{O}$ .

The number of atoms on the reactant side is:

  $\begin{array}{l}\text{Fe = 2}\\ \text{O = 3}\\ \text{H = 2}\end{array}$

The number of atoms on the product side is:

  $\begin{array}{l}\text{Fe = 1}\\ \text{O = 1}\\ \text{H = 2}\end{array}$

From the above number of atoms in the reactant and product side, it can be concluded that the only number of atoms for hydrogen are same whereas the number of atoms for iron and oxygen is different. So, to balance the reaction, ${\text{H}}_{\text{2}}$ in reactant side is multiplied by coefficient 3 and $\text{Fe}$ and ${\text{H}}_{\text{2}}\text{O}$ in product side and multiplied by 2 and 3 coefficients respectively. Thus, the balanced chemical reaction is:

  ${\text{Fe}}_{\text{2}}{\text{O}}_3{\text{ + 3H}}_{\text{2}}\to {\text{ 2Fe + 3H}}_{\text{2}}\text{O}$

Hence, the coefficient of ${\text{H}}_{\text{2}}$ after balancing reaction, ${\text{Fe}}_{\text{2}}{\text{O}}_3{\text{ + H}}_{\text{2}}\to {\text{ Fe + H}}_{\text{2}}\text{O}$ is 3.