Question 6.8: NO2(g) and N2O4(g) are in a reaction vessel with partial pre...

Thermodynamics, Statistical Thermodynamics, & Kinetics

$NO_{2}\left(g\right)$ and $N_{2} O_{4}\left( g \right)$ are in a reaction vessel with partial pressures of 0.350 and 0.650 bar, respectively, at 298 K. Is this system at equilibrium? If not, will the system move toward reactants or products to reach equilibrium?

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The reaction of interest is $2 NO_{2}\left( g \right)\rightleftharpoons N_{2}O_{4}\left( g \right)$ . We calculate $\Delta G_{R}$ using $\Delta G_{R} = \Delta G°_{R} +RT \ln QP$

\Delta G_{R} =99.8 KJ mol^{-1} -2 × 51.3 KJ mol^{-1} + 8.314 J mol^{-1} K^{-1}

× 298 K \ln \frac{0.650 bar /1 bar }{\left( 0.350 bar /1 bar \right)^{2}}

=-2.80 × 10^{3} J mol^{-1} + 4.13 × 10^{3} J mol^{-1}

=1.33× 10^{3} J mol^{-1}

Since $\Delta G_{R}\neq 0$ , the system is not at equilibrium, and because $\Delta G_{R} \gt 0$ , the system moves toward reactants.

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