Chapter 17, Problem 94A

Interpretation Introduction

Interpretation:

The chemical reaction is balanced in which way needs to be explained.

Concept introduction

A reaction is said to be balanced if the number of atoms for each element on reactants side is equal to the number of atoms for each element on product side of a reaction.

Answer to Problem 94A

A reaction is balanced only if the number of atoms for each element of reactants are equal to the number of atoms for each element on product side.

Explanation of Solution

Let us discuss the balancing process of a chemical equation with the help of a reaction which is given below

${\text{PCl}}_{\text{5}}{\text{+ H}}_{\text{2}}{\text{O = H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{+ HCl}$

so, The balanced equation is

${\text{PCl}}_{\text{5}}{\text{+ 4H}}_{\text{2}}{\text{O = H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{+ 5HCl}$

Explanation:

Left side Right side

$\begin{array}{l}\text{P=1 P =1}\hfill \\ \text{Cl =5 Cl =1}\hfill \\ \text{H=2 H=3+1}\hfill \\ \text{O=1 O= 4}\hfill \end{array}$

Now we start balancing the easiest element such as $\text{Cl}$

Left side Right side

$\begin{array}{l}\text{P=1 P =1}\hfill \\ \text{Cl =5 Cl = 1×5 = 5}\hfill \\ \text{H=2 H= 3+ }\left(\text{1×5}\right)\text{ = 8}\hfill \\ \text{O=1 O = 4}\hfill \end{array}$

Now equation becomes

${\text{PCl}}_{\text{5}}{\text{+ H}}_{\text{2}}{\text{O = H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{+ 5HCl}$

Now we balancing the H atom

Left side Right side

$\begin{array}{l}\text{P=1 P=1}\hfill \\ \text{Cl=5 Cl= 1×5 =5}\hfill \\ \text{H= 2×4 = 8 H= 3+ }\left(\text{1×5}\right)\text{ = 8}\hfill \\ \text{O= 1×4= 4 O= 4 }\hfill \end{array}$

So, finally the given equation is balanced

${\text{PCl}}_{\text{5}}{\text{+ 4H}}_{\text{2}}{\text{O = H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{+ 5HCl}$

Hence, in this way a given equation becomes balanced.

The proportion of water and phosphoric acid are 4 and 1 after the balancing process.

Conclusion

A balanced chemical equation takes place when the number of different atoms of elements in the reactants side is equal to that of the product side.