Chapter U4, Problem 4STP

Interpretation Introduction

Interpretation:

The balanced chemical equation that represents a physical change needs to be determined.

Concept introduction:

The change that affects only the form of a chemical substance but the chemical composition remains same is said to be physical change.

Answer to Problem 4STP

The correct option is (b), ${\text{N}}_{\text{2}}\text{(l)}\to {\text{N}}_{\text{2}}\text{(g)}$

Explanation of Solution

Reason for correct option:

${\text{N}}_{\text{2}}\text{(l)}\to {\text{N}}_{\text{2}}\text{(g)}$

The above chemical equation represents a physical change as the nitrogen changes its state from liquid to gas but composition of nitrogen remains same throughout the process that is, ${\text{N}}_{\text{2}}$.

Conclusion

Reason for incorrect options:

The following chemical equations represents a chemical change where the composition of the reactants and products are different

${\text{2H}}_{\text{2}}{\text{(g) + O}}_{\text{2}}\text{(g)}\to {\text{2H}}_{\text{2}}\text{O(l)}$

In this reaction, hydrogen gas combines with oxygen gas to produce a new compound that is liquid water.

${\text{2KClO}}_3\text{(s) }\to {\text{ 2KCl(s) + 3O}}_{\text{2}}\text{(g)}$

In this reaction, solid potassium chlorate decomposes to produce a new compound that is solid potassium chloride and oxygen gas.

$\text{Zn(s) + 2HCl(aq)}\to {\text{ ZnCl}}_{\text{2}}{\text{(aq) + H}}_{\text{2}}\text{(g)}$

In this reaction, solid zinc reacts with aqueous hydrogen chloride to produce a new compound that is aqueous zinc chloride and hydrogen gas.