Ammonia has been studied as an alternative \"clean\" fuel for internal combustio

Question

Ammonia has been studied as an alternative "clean" fuel for internal combustion engines, since its reaction with oxygen produces only nitrogen and water vapor, and in the liquid form it is easily transported. An industrial chemist studying this reaction fills a 1.5 L flask with 4.1 atm of ammonia gas and 4.9 atm f oxygen gas at 31.°C. He then raises the temperature, and when the mixture has come to equilibrium measures the partial pressure of water vapor to be 1.2 atm. Calculate the pressure equilibrium constant for the combustion of ammonia at the final temperature of the mixture. Round your answer to 2 significant digits K= x10

Explanation / Answer

Initial pressure of NH3 = 4.1 atm

Initial pressure of O2 = 4.9 atm

The balanced reaction with ICE TABLE

4NH3 (l) + 3 O2 (g) ---> 2N2 (g) + 6H2O (g)

I 4.1 4.9

C - 4x - 3x +2x +6x

C (4.1-4x) (4.9-3x) 2x 6x

At equilibrium

Partial pressure of water vapor = 1.2 atm

6x = 1.2

x = 0.2 atm

PNH3 = 4.1 - 4*0.2 = 3.3 atm

PO2 = 4.9 - 3*0.2 = 4.3 atm

PN2 = 2*0.2 = 0.4 atm

Equilibrium constant expression of the reaction

Kp = [PH2O]6[PN2]2/ [PO2]3[PNH3]4

= [1.2]6[0.4]2/ [4.3]3[3.3]4

= 5.1 x 10^-5

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