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 25.0 L tank with 3.8 mol of ammonia gas and 2.3 mol of oxygen gas at 53. °C. He then raises the temperature, and when the mixture has come to equilibrium measures the amount of water vapor to be 3.2 mol. Calculate the concentration equilibrium constant for the combustion of ammonia at the final temperature of the mixture. Round your answer to 2 significant digits D:10

Explanation / Answer

Initial concentration of NH3 = moles/Volume

= 3.8 mol / 25 mL x 1L/1000mL

= 152 M

Initial concentration of O2 = 2.3/0.025 = 92 M

The balanced reaction with ICE TABLE

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

I 152 92

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

C 152-4x 92-3x 2x 6x

At equilibrium

Moles of water vapor = 3.2 mol

Concentration of H2O = 3.2/0.025 = 128 M

6x = 128

x = 21.33 M

[NH3] = 152 - 4*21.33 = 66.68 M

[O2] = 92 - 3*21.33 = 28.01 M

[N2] = 2*21.33 = 42.66 M

Equilibrium constant expression of the reaction

K = [H2O]6[N2]2/ [O2]3[NH3]4

= [128]6[42.66]2/ [28.01]3[66.68]4

= 1.8 x 10^4

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