Chapter 20.3, Problem 20.7BFP

Interpretation Introduction

Interpretation:

The signs and relative magnitudes $\Delta H^o$, $\Delta S^o$ and $\left(-T\Delta S^o\right)$ for given reaction process have to be identified at $-{40}^{o}C$.

Concept introduction:

Entropy$\left(S\right)$: it is used to describe the disorder. It is the amount of arrangements possible in a system at a particular state.

  If the disorder increases in a system, then $\Delta S>0$ positive

If the disorder decreases in a system, then $\Delta S<0$ negative

If the disorder equal in a system, then $\Delta S=0$

Standard free energy is the term that is used to explain the total energy content in a thermodynamic system that can be converted into work.  The free energy is represented by the letter $G^o$.  All spontaneous process is associated with the decrease of free energy in the system.  The equation given below helps us to calculate the change in free energy in a system.

  ${\text{ΔG}}_{\text{rxn}}^{\text{o}}\text{ = }\Delta {{\rm H}}_{\text{rxn}}^{\text{o}}\text{- T}\Delta {\text{S}}_{\text{rxn}}^{\text{o}}$

Where,

  ${\text{ΔG}}_{\text{rxn}}^{\text{o}}$ is the change in standard free energy of the system

  $\Delta {{\rm H}}_{\text{rxn}}^{\text{o}}$ is the change in standard enthalpy of the system

  $\text{T}$ is the absolute value of the temperature

  $\Delta {\text{S}}_{\text{rxn}}^{\text{o}}$ is the change in entropy in the system

Free energy change$\left(\Delta G\right)$: change in the free energy takes place while reactants convert to product.

Spontaneous reactions releases the free energy and has $\Delta G<0$ (exothermic)

Nonspontaneous reactions absorbs the free energy and has $\Delta G>0$ (endothermic)