Chapter 23, Problem 23.25P

Interpretation Introduction

Interpretation:

Value of ${\text{ΔG}}_{rxn}^o$ at $250°C$ has to be calculated. The direction in which the reaction is spontaneous under standard conditions has to be identified. Also, the value of ${\text{ΔG}}_{rxn}$ and direction in which the reaction is spontaneous has to be determined when $P_{PC{l}_3}=\text{ 0}{\text{.20 bar, P}}_{C{l}_2}=\text{ 0}\text{.80 bar}$ and $P_{PC{l}_5}=\text{ 1}\text{.0}\times {\text{10}}^{-6}\text{ bar}$.

Concept Introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by $\Delta G$. Value of $\Delta G_{rxn}^o$ is determined as follows,

  ${\text{ΔG}}_{rxn}^o=-\text{RT}\text{ln K}$

Under standard conditions, the reaction is spontaneous when $\Delta G_{rxn}^o$ is negative whereas the reaction is not spontaneous when $\Delta G_{rxn}^o$ is positive.

The formula of ${\text{ΔG}}_{\text{rxn}}$ in is given below,

    ${\text{ΔG}}_{rxn}=\text{RT}\text{ln }\left(\frac{{\text{Q}}_c}{K_c}\right)$

If $Q_c>{\text{ K}}_c$ then the reaction is spontanous in backward reaction (from right to left).

If $Q_c{\text{< K}}_c$ then the reaction is spontanous in forward reaction (from left to right).

If $Q_c={\text{ K}}_c$ then the reaction will be at equilibrium.