Chapter 18, Problem 77A

(a)

Interpretation Introduction

Interpretation: A reaction's entropy increase or decrease is to be determined.

Concept Introduction: Entropy is defined as the measurement of the degree of randomness. The increase in a system's degree of disorder is referred to as an increase in entropy.

Answer to Problem 77A

In the given reaction, entropy increases due to the decomposition process in which a solid reactant decomposes and generates a gaseous product in which disorder and randomness are increased.

Explanation of Solution

The give reaction is as follows:

  ${\text{CaCO}}_3\left(s\right)\to \text{CaO}\left(s\right)+{\text{CO}}_2\left(g\right)$

The decomposition reaction of solid ${\text{CaCO}}_3$ into solid and gaseous products. Solid ${\text{CaCO}}_3$ and $\text{CaO}$ has a well-organized, stable, and orderly structure. The gaseous ${\text{CO}}_2$ has a higher entropy than a solid substance because its particles are in continuous, disorderly motion.

Therefore, the entropy increases in the given reaction.

(b)

Interpretation Introduction

Interpretation: A reaction's entropy increase or decrease is to be determined.

Concept Introduction: Entropy is defined as the measurement of the degree of randomness. The increase in a system's degree of disorder is referred to as an increase in entropy.

Answer to Problem 77A

In the given reaction, entropy decreases as a result of the production of a solid product with an ordered structure from gaseous reactants with a greater degree of disorder and randomness.

Explanation of Solution

The give reaction is as follows:

  ${\text{NH}}_3\left(g\right)+\text{HCl}\left(g\right)\to {\text{NH}}_{\text{4}}\text{Cl}\left(s\right)$

The reaction produces solid ${\text{NH}}_{\text{4}}\text{Cl}$ from gaseous ${\text{NH}}_3$ and $\text{HCl}$ reactants. As a result of the continual, disorderly motion of particles in gaseous molecules, gases have a higher entropy than solids and liquids. The structure of a solid ${\text{NH}}_{\text{4}}\text{Cl}$ is well-organized, a stationary and orderly system.

Therefore, the entropy decreases in the given reaction.