Chapter 18, Problem 50QP

Interpretation Introduction

Interpretation:

The spontaneity for the given equilibrium process at 25°Cis to be determined and the reason for diamonds do not become graphite on standing is to be stated.

Concept introduction:

Reaction quotient is the ratio of molar concentration of the ions or the partial pressure of the gaseous atoms or molecules in the product side to the reactant side, raised to the power of their stoichiometric coefficients in the balanced chemical reaction.

For a general chemical reaction, $\text{aA + bB }\underset{}{\overset{}{\rightleftarrows }}\text{cC+dD}$, the reaction quotient is represented as follows:

$Q=\frac{{\text{[C]}}^{\text{c}}{\text{[D]}}^{\text{d}}}{{\text{[A]}}^{\text{a}}{\text{[B]}}^{\text{b}}}$

The relation between free energy change and standard free energy change is as follows:

$\Delta G=\Delta G^o+\text{R}T\ln Q$

Here, $\Delta G$ is free energy change, $\Delta G^o$ is the standard free energy change, $Q$ is reaction quotient, $\text{R}$ is gas constant, and $T$ is the absolute temperature at which the reaction takes place.

The value of $\Delta G$ for a reaction to be spontaneous must be negative.

The value of $\Delta G$ for a reaction at equilibrium must be zero.

The value of $\Delta G$ for a reaction to be nonspontaneous must be positive.

The standard free energy change of the reaction is the difference of the sum of the standard free energy change of the products and the sum of the standard free energy change of the reactants.

The expression is as follows:

$\Delta {\mathit{\text{G}}}_{reaction}^{\circ }\text{=}{\displaystyle \sum \Delta {\mathit{\text{G}}}_{product}^{\circ }}-{\displaystyle \sum \Delta {\mathit{\text{G}}}_{reac\tan t}^{\circ }}$