Chapter 13, Problem 1KSP

Which of the following processes is accompanied by an increase in entropy? (Select all that apply.)

$\begin{array}{l}\left(\text{a}\right)\hfill \\ {\text{Br}}_{\text{2}}\left(l\right)\underset{}{\to }{\text{ Br}}_{\text{2}}\left(g\right)\hfill \\ \left(\text{b}\right)\hfill \\ {\text{NH}}_{\text{3}}\left(g\right)\text{ + HCl}\left(\text{g}\right)\underset{}{\to }{\text{ NH}}_{\text{4}}\text{Cl}\left(s\right)\hfill \\ \left(\text{c}\right)\hfill \\ \text{NaCl}\left(s\right)\underset{}{\to }{\text{Na}}^{\text{+}}\left(g\right)\text{ + Cl }\left(g\right)\hfill \\ \left(\text{d}\right)\hfill \\ {\text{H}}_{\text{2}}\left(g\right){\text{ + O}}_{\text{2}}\left(g\right)\underset{}{\to }{\text{2H}}_{\text{2}}\text{O(}l\text{)}\hfill \end{array}$

Interpretation Introduction

Interpretation:

The processes accompanied by an increase in entropy are to be determined.

Concept introduction:

Entropy is the measure of randomness in a thermodynamic system. The second law of thermodynamics states that the entropy of an isolated system never decreases. Such systems spontaneously evolve towards thermodynamic equilibrium, the state with maximum entropy.

The processes in which entropy increases are called endothermic processes.

The processes in which entropy decreases are called exothermic processes.

Answer to Problem 1KSP

Correct answer:Options (a) and(c).

Explanation of Solution

Reasons for the correct options:

The reaction is shown below:

${\text{Br}}_{\text{2}}\left(l\right)\to {\text{BR}}_{\text{2}}\left(g\right)$

In the given reaction, bromine changes from the liquid state to the gaseous state. In the conversion of a liquid to its gaseous state, the volume occupied by the molecules increases. The particles are no longer locked in a place. Because they are now free to move, they can distribute themselves in more ways. Gases have the highest entropy values because they have the greatest freedom of movement. Therefore, the entropyfor this process increases.

The reaction is shown below:

$\text{NaCl}\left(s\right)\to {\text{Na}}^{+}\left(g\right)+{\text{Cl}}^{-}\left(g\right)$

In the given reaction, solid sodium chloride is converting into its gaseous state. When a solid gets converted into thegaseous state, the molecules are free to move, due to which the distribution of energy increases and hence, entropy increases.

Hence, options(a) and(c) are correct.

Reasons for the incorrect option:

The reaction is as follows:

${\text{NH}}_{\text{3}}\left(g\right)+\text{HCl}\left(g\right)\to {\text{NH}}_{\text{4}}\text{Cl}\left(s\right)$

The given reaction is option (b). It is incorrect because in this reaction, entropy decreases as the gaseous state gets converted to the solid state, that is, the volume occupied by molecules is decreasing. The particles in solid state are locked in place and highly ordered. So, it is an incorrect answer.

The reaction is as follows:

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

The given reaction is option(d). It is incorrect because in this reaction, entropy decreases as the gaseous state gets converted to theliquid state, that is, the volume occupied by molecules is decreasing. So, it is an incorrect answer.

Hence, options (b) and (d) are incorrect.