Nitrogen dioxide is one of the many oxides of nitrogen (often collectively calle

Question

Nitrogen dioxide is one of the many oxides of nitrogen (often collectively called "NOx") that are of interest to atmospheric chemistry. It can react with itself to form another form of NOx, dinitrogen tetroxide A chemical engineer studying this reaction fills a 500. mL flask at 12. °C with 0.98 atm of nitrogen dioxide gas. He then raises the temperature considerably, and when the mixture has come to equilibrium determines that it contains 0.28 atm of nitrogen dioxide gas The engineer then adds another 0.25 atm of nitrogen dioxide, and allows the mixture to come to equilibrium again. Calculate the pressure of dinitrogen tetroxide after equilibrium is reached the second time. Round your answer to 2 significant digits. atm x10

Explanation / Answer

Calculate Kp

2NO2 --> N2O4

[NO2] initial = 0.98 atm

at equilibrium,

[NO2] = 0.28 atm

change = 0.98 - 0.28 = 0.70 atm

2 moles of NO2 gives 1 mole N2O4

[N2O4] at equilibrium = 0.70/2 = 0.35 atm

So,

Kp = 0.35/(0.28)^2 = 4.46

Now we added another 0.25 atm NO2

total [NO2] = 0.28 + 0.25 = 0.53 atm

           2NO2 --> N2O4

I           0.53         0.35

C         -2x          +x

E       0.53-2x   0.35+x

So,

Kp = [N2O4]/[NO2]^2

4.46 = (0.35+x)/(0.53-2x)^2

1.25 - 9.45x + 18x^2 = 0.35 + x

18x^2 - 10.45x + 0.9 = 0

x = 0.1052 atm

So,

equilibrium N2O4 = 0.35 + 0.1052 = 0.4552 atm

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