Question

Ammonia is created in the Haber process in a rigid container (nitrogen gas plus hydrogen gas react to form ammonia gas) at a constant temperature. 5 moles of hydrogen gas are mixed with 10 moles of nitrogen gas. The initial pressure exerted on the container is 10 atm. Assuming the reaction runs to completion, what will the pressure (in atm) on the vessel be after the reaction takes place?

Answer 1

The reaction taking place is:
N2 (g) + 3 H2 (g) --> 2 NH3 (g)

5 moles of H2 will react with 5/3 moles of H2 to form 10/3 moles of NH3
So, after reaction we have:
moles of H2 = 0
moles of N2 = 10 - 5/3 = 25/3 moles
moles of NH3 = 10/3 moles

Total moles of gas after reaction = 25/3 + 10/3 = 35/3 moles

Initially, when number of moles where 15, pressure was 10 atm

use:
Pi/ni = Pf/nf
10/15 = Pf / (35/3)
10/15 = 3*Pf /35
Pf = 350/45 = 70/9 atm = 7.78 atm

Answer : 7.78 atm