Question

A sample of ammonia gas is completely decomposed to nitrogen andhydrogen gases over heated iron wool. If the total pressure is 639mmHg, calculate the partial pressure of N2 and H2. Enter your answers in scientific notations

Answer 1

The reaction takes place is   NH₃ (g) (1/2) N₂ (g) + (3/2)H₂ (g)

Given that ammonia gas is completely decomposed to nitrogen and hydrogen gases , so there is no ammonia left in the mixture.There is only N₂ & H₂ in the mixture.

According to Dalton's law of partial pressures ,

partial pressure of N₂ + partial pressure of H₂ = toatl pressure = 639 mm Hg

Since there is 1/2 mole N₂ & 3/2 moles H₂ in the mixture.

Let a be the partial pressure of N₂, the partial pressure of H₂ is therefore 3a.

So total pressure = a + 3a = 639 mm Hg

                                     4a = 639

                                       a = 159.75 mm Hg

The partial pressure of N₂ is , p_N2 is a = 159.75 mm Hg

      partial pressure of H₂ is , p_H2 is 3a = 3x159.75 mm Hg

                                                            = 479.25 mm Hg