Be sure to answer all parts. The equilibrium constant ( K P ) for the formation

Question

Be sure to answer all parts.

The equilibrium constant (KP) for the formation of the air pollutant nitric oxide (NO) in an automobile engine at 537

°

C is 4.5

×

1011.

N2(g) + O2(g) 2NO(g)

(a) Calculate the partial pressure of NO under these conditions if the partial pressures of nitrogen and oxygen are 3.00 and 0.012 atm, respectively.

×

10

atm

(b) Repeat the calculation for atmospheric conditions in which the partial pressures of nitrogen and oxygen are 0.78 and 0.21 atm, and the temperature is 25

°

C. (The KP for the reaction is 4.0

×

1031 at this temperature.)

×

10

atm

(c) Is the formation of NO endothermic or exothermic?

endothermic

exothermic

endothermic

exothermic

Explanation / Answer

a) we know that Kp for the given reaction will be

N2 + O2 --> 2NO

Kp = p(NO)2 / pN2 X pO2 = 4.5 X 10^-11

4.5 X 10^-11 = p(NO)2 / 3 X 0.012

p(NO)2 = 1.62 X 10^-12

pNO = 1.27 X 10^-6 atm

b) Kp = 4 X 10^-31 = p(NO)2 / pN2 X pO2

4 X 10^-31 = p(NO)2 / 0.78 X 0.21

p(NO)2 = 6.552 X 10^-32

pNO = 2.56 X 10^-16 atm

c) it is an endothermic reaction. The enthalpy of reaction is positive.

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