Chapter 18, Problem 48QP

Interpretation Introduction

Interpretation:

The standard free energy change for the formation of one mole ${\text{COCl}}_{\text{2}}$ at 25°Cis to be determined.

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 stochiometric 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:

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

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

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

Here, $\Delta G$ is free energy change, $\Delta G^o$ is standard free energy change, $Q$ is reaction quotient, $\text{R}$ is gas constant, and $T$ is the absolute temperatureat 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 non-spontaneous must be positive.

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

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