Chapter 18, Problem 18.15QP

Interpretation Introduction

Interpretation:

The usage of different sign combinations of standard enthalpy change and standard entropy change in predicting the spontaneity of reactions has to be explained.

Concept introduction:

Free energy:

Free energy is measured by subtracting the product of temperature and entropy from the enthalpy of a system.

$\begin{array}{l}\text{G}\text{=}\text{H}\text{-}\text{TS}\\ \text{where,}\\ \text{G}\text{-}\text{free}\text{energy;}\text{H}\text{-}\text{enthalpy}\\ \text{S}\text{-}\text{entropy and T}\text{-temperature}\text{.}\end{array}$

Relationship between ${\text{ΔG}}^{\text{o}}\text{,}{\text{ΔH}}^{\text{o}}\text{and}{\text{ΔS}}^{\text{o}}$ is given by

$\begin{array}{l}{\text{ΔG}}^{\text{o}}\text{=}{\text{ΔH}}^{\text{o}}\text{-}{\text{TΔS}}^{\text{o}}\\ \text{where,}\\ {\text{ΔG}}^{\text{o}}\text{-}\text{standard}\text{free}\text{energy}\text{change;}{\text{ΔH}}^{\text{o}}\text{-}\text{standard}\text{enthalpy}\text{change}\\ {\text{ΔS}}^{\text{o}}\text{-}\text{standard}\text{entropy}\text{change and T}\text{-}\text{temperature}\end{array}$

Spontaneous process:

The chemical or physical change can takes place by itself without the help of surroundings are called as spontaneous process.

To explain: the different sign combinations of standard enthalpy change and standard entropy change