Chapter 18, Problem 18.80SP

Interpretation Introduction

Interpretation:

The reason for signs of $\Delta H$ and $\Delta S$ to predict spontaneity of reaction at constant $T$ and $P$ should be explained.

Concept introduction:

The relation of total entropy is as follows:

$\Delta S_{\text{total}}=\Delta S_{\text{system}}+\Delta S_{\text{surroundings}}$

Where,

• $\Delta S_{\text{surr}}$ is entropy change for surrounding.
• $\Delta S_{\text{system}}$ is entropy change of system.
• $\Delta S_{\text{total}}$ is total entropy.

Second law of thermodynamics provides criteria for spontaneity. It states that when sign of total entropy change is positive, the reaction is spontaneous and when sign of $\Delta S_{\text{total}}$ is negative, the reaction is nonspontaneous. Also, all reactions are at equilibrium when total entropy change is equal to zero.