A sample of solid NH4NO3 was placed in an evacuated container and then heated so that it decomposed explosively according to the following equation:

NH4NO3(s) N2O(g) + 2H2O(g)

At equilibrium, the total pressure in the container was found to be 2.72 bar at a temperature of 500.°C. Calculate Kp.

a.

1.64

b.

0.822

c.

2.98

d.

80.5

e.

0.745

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At equilibrium, the total pressure in the container was found to be 2.72 bar at a temperature of 500.°C.

NH4NO3(s) N2O(g) + 2H2O(g)

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Kp is 2.98  (option c.)

Explanation:

The decomposition is:

NH₄NO₃(s) →  N₂O(g) + 2H₂O(g)

Total pressure at equilibrium is 2.72 bar so, in order to determine Kp we need the partial pressure and we only have total pressure.

According to stoichiometry, nitrogen oxide increase by 1, the partial pressure and water vapor, by 2.

Total pressure is: Partial pressure N₂O + Partial pressure H₂O

2.72 bar = X + 2X → X = 2.72 bar / 3 = 0.91 bar

Partial pressure N₂O = 0.91 bar

Partial pressure H₂O = 1.81 bar

We make the expression for Kp = Partial pressure N₂O . (P. pressure H₂O)²

Kp = 0.91 . 1.81² = 2.98

We do not consider the ammonium nitrate, because it is solid

3 hours because it is a decent distance.