A sealed tube containing an equilibrium mixture of NO2(g) (brown) and N2O4(g) (c

Question

A sealed tube containing an equilibrium mixture of NO2(g) (brown) and N2O4(g) (colorless) is subjected to a variety of temperatures. For the equilibrium reaction shown, the values of the DH°rxn and DS°rxn are also shown. What is observed in the tube with increasing temperature? 2NO2(g) N2O4(g) DH° = -58.02 kJ/mol, DS° = -176.5 J/mol × K

a. At higher temperatures, the gas in the tube has a darker brown color.

b. The color does not change with temperature.

c. At higher temperatures, the gas in the tube is colorless.

d. At higher temperatures, the gas turns green.

e. At higher temperatures, the gas in the tube has a lighter brown color.

Explanation / Answer

a. At higher temperatures, the gas in the tube has a darker brown color.

2NO2(g) N2O4(g)

DH° = -58.02 kJ/mol and DS° = -176.5 J/mol K

Frozen N2O4 is nearly colorless

N2O4(g) -----> 2 NO2(g)

As N2O4 is warmed above its boiling point, it starts to dissociate into brown NO2 gas.

Eventually the color stops changing as N2O4(g) and NO2(g)reach concentrations at which they are interconverting at the same rate. The two gases are in equilibrium.

N2O4(g) ------> 2 NO2(g)

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