Question 6.11: Using the result of Example Problem 6.10 and the data tables...

Using the result of Example Problem 6.10 and the data tables, consider the dissociation equilibrium Cl_{2}\rightleftharpoons 2Cl\left( g \right).

a. Calculate K_{P} at 800. K, 1500. K, and 2000. K for P=0.010 bar.

b. Calculate the degree of dissociation \alpha at 300. K, 1500. K, and 2000. K.

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a.   \Delta G°_{R}=2\Delta G°_{f}\left( Cl,g \right)-\Delta G°_{f}\left( Cl_{2},g \right)=2×105.7 ×10^{3}  J  mol^{-1} -0

=211.4  kJ  mol^{-1}

 

\Delta H°_{R}=2\Delta H°_{f}\left( Cl,g \right)-\Delta H°_{f}\left( Cl_{2},g \right)=2×121.3 ×10^{3}  J  mol^{-1}-0

 

=242.6  kJ  mol^{-1}

 

\ln K_{P}\left( T_{f} \right)=-\frac{\Delta G°_{R}}{RT}-\frac{\Delta H°_{R}}{R}\left( \frac{1}{T_{f}} -\frac{1}{298.15 K}\right)

 

=-\frac{2114 ×10^{3}  J  mol^{-1}}{8.314 J K^{-1}  mol^{-1} ×298.15  k}-\frac{242.6×10^{3}  J  mol^{-1} }{8.314  J  K^{-1}  mol^{-1}}

 

×\left( \frac{1}{T_{f}}-\frac{1}{298.15  K}\right)

 

\ln K_{P}\left( 800. K \right)

 

=-\frac{211.4 ×10^{3}  J  mol^{-1}}{8.314 J K^{-1}×298.15 K} -\frac{242.6×10^{3}  J  mol^{-1}}{8.314 J K^{-1} mol^{-1}}

 

×\left( \frac{1}{800. K} -\frac{1}{298.15 K}\right)=-23.888

 

K_{P}\left( 800. K \right)=4.22×10^{-11}

The values for K_{P} at 1500. and 2000. K are 1.03×10^{-3} and 0.134, respectively.

b. The value of \alpha at 2000. K is given by

\alpha=\sqrt{\frac{k_{P}\left( T \right)}{K_{P}\left( T \right)+4\frac{P}{P°}}}=\sqrt{\frac{0.134}{0.134+4 ×0.01}}=0.878

The values of \alpha at 1500. and 800. K are 0.159 and 3.23×10^{-5}, respectively.

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