Question

Which change occurs with the largest increase in entropy at $\text{2}{\text{5}}^{\text{o}}\text{C}$?
A. $B{r}_2\left(l\right)\to B{r}_2\left(g\right)$
B. $C_{\left(graphite\right)}\to C_{\left(diamond\right)}$
C. $H_{2}O\left(s\right)\to H_{2}O\left(l\right)$
D. $HCl\left(g\right)+H_{2}O\left(l\right)\to H_3{O}^{+}\left(aq\right)+C{l}^{-}\left(aq\right)$

Answer 1

Hint: In classical thermodynamics, we can say that the second law of thermodynamics describes entropy of an isolated system remains constant (or) always increases. So, entropy is a measure of tendency of processes like chemical reaction, to be entropically favored (or) to move in a specific direction. We can use the term microstates to explain the number of various possible arrangements of molecular position and kinetic energy at a specific thermodynamic state.

Complete step by step answer:
We could break down change in entropy as a result from changes in specific properties of our system. There are changes in five parameters, which would bring up an entropy change of the system.
Temperature
Volume
Phase
Mixing
Composition
As we know that the entropy of a system would increase in a process which gives an increase in the number of microstates.
Changes in entropy also rise due change in phase. Certain phases contain a larger number of microstates and this leads to higher energy.
We must know that the solids contain few microstates, so they have lowest entropy. Liquid contains more microstates, so they have higher entropy. Gas has much more microstates when compared to solids and liquids, so the entropy would be highest for gas.
In the given options, we can see that liquid bromine is converted to gaseous bromine, therefore that microstates would also become more and entropy would be greater. Therefore, the option (A) is correct.
Since, the microstates of gases and liquids will be less when compared to microstates of gases, the entropy of the system would also be less.
Therefore, the options (B), (C), and (D) are incorrect.

So, the correct answer is Option A .

Note:
We must remember that the changes in entropy would also be seen due to changes in temperature. Higher the temperature, the system would have more thermal energy, the ways to distribute energy would be more, and the entropy of the system would increase. So, increasing the temperature, the entropy of the system would increase.
When the substances are mixed, the entropy of the system would increase. This is because there are many more microstates for the mixed system when compared to un-mixed systems. If there are many microstates, the greater would be the entropy.