Chapter 18, Problem 18.106SP

Interpretation Introduction

Interpretation:

The relationship between free-energy change under nonstandard state condition $\left(\Delta G\right)$, under standard-state conditions $\left(\Delta G°\right)$, and reaction quotient $\left(Q\right)$ is to be determined.

Concept introduction:

The relation of total entropy is as follows:

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

Second law of thermodynamics gives criteria for spontaneity. It states that when sign of total entropy change is positive, the reaction is spontaneous. 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 0.

The relationship between $\Delta H$ and $\Delta S$ is as follows:

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

Where,

• $\Delta G$ is free energy change.
• $\Delta H$ is enthalpy change.
• $T$ is temperature.
• $\Delta S$ is change in entropy.

The entropy criteria for spontaneous change at constant $T$ and $P$ can also be stated with respect to free energy change as follows:

(1) When $\Delta G<0$, reaction is a spontaneous.

(2) When $\Delta G>0$, reaction is nonspontaneous.

(3) When $\Delta G=0$, reaction is at equilibrium.