Practice Problem 11

Use values of  deltaHo and deltaSo for the following reaction at 25C to estimate the equilibrium constant for this reaction at the temperature of boiling water (100C), ice(0C), a dry ice-acetone bath (-78C), and liquid nitrogen (-196C):

2 NO2(gequilibr.gif (63 bytes) N2O4(g)


Answer

100C:    Kp = 0.067

0C:        Kp = 58

-78C:    Kp = 1.4 x 106

-196C:   Kp   = 3.8 x 1029

At 100C, the unfavorable entropy term is relatively important, and the equilibrium lies on the side of NO2.  As the reaction is cooled, the entropy term becomes less important, and the equilibrium shifts toward N2O4.   At the temperature of liquid nitrogen all of the NO2 condenses to form N2O4.

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