Chapter 16, Problem 16.61SP

(a)

Interpretation Introduction

Interpretation:

$\Delta S_{total}$ for the reaction of $ZnS$ with $O_2$ has to be calculated.

Concept Introduction:

• Entropy refers to measurement of randomness or disorderliness in the system.  More the number of molecules in a system more will be the movement of molecules and greater will be the entropy given that weak intermolecular forces prevails between molecules.
• Entropy is denoted by ‘S’ and $\Delta S$  change in entropy.
• $\Delta S°$ refers to standard entropy of the reaction which is termed as entropy change in a reaction under standard conditions of $298K$ and $1\text{ atm}$ pressure.  It is represented as,

$\Delta S°=S°\left(products\right)-S°\left(reac\tan ts\right)$

• $\Delta S_{total}=\Delta S_{sys}+\Delta S_{surr}$

Where,

 $\begin{array}{l}\Delta S_{total}=total\text{ entropy change}\\ \Delta S_{sys}=\text{entropy change in system (reaction)}\\ \Delta S_{surr}=\text{entropy change in surroundings}\end{array}$

• $\Delta H$ refers to change in enthalpy.  $\Delta S_{surr}$ and $\Delta H°$ are related as,

$\Delta S_{surr}=\frac{-\Delta H°}{T}$

(b)

Interpretation Introduction

Interpretation:

The temperature at which reaction of $ZnS$ with $O_2$ become non-spontaneous has to be explained.

Concept Introduction:

• Entropy refers to measurement of randomness or disorderliness in the system.  More the number of molecules in a system more will be the movement of molecules and greater will be the entropy given that weak intermolecular forces prevails between molecules.
• Entropy is denoted by ‘S’ and $\Delta S$  change in entropy.
• $\Delta S°$ refers to standard entropy of the reaction which is termed as entropy change in a reaction under standard conditions of $298K$ and $1\text{ atm}$ pressure.  It is represented as,

$\Delta S°=S°\left(products\right)-S°\left(reac\tan ts\right)$

• $\Delta S_{total}=\Delta S_{sys}+\Delta S_{surr}$

Where,

 $\begin{array}{l}\Delta S_{total}=total\text{ entropy change}\\ \Delta S_{sys}=\text{entropy change in system (reaction)}\\ \Delta S_{surr}=\text{entropy change in surroundings}\end{array}$

• $\Delta H$ refers to change in enthalpy.  $\Delta S_{surr}$ and $\Delta H°$ are related as,

$\Delta S_{surr}=\frac{-\Delta H°}{T}$

• The term free energy G,  refers to energy available in the system to do work.  Change in free energy is denoted by $\Delta G$ and it is represented as,

$\Delta G=\Delta H-T\Delta S$

• The temperature at which a spontaneous reaction becomes non-spontaneous and vice-versa is termed as crossover temperature.