A sample of NH3(g) is placed in a rigid container. When the equilibrium below is established, the partial pressure of hydrogen gas is 0.978 atm. What is the partial pressure of N2(g) at equilibrium?

PpN₂ = 0.326 atm

Explanation:

In this case, let's write the equilibrium reaction taking place here:

2NH₃(g) <> 3H₂(g) + N₂(g)

Now, we know that when the reaction reach the equilibrium the partial pressure of H₂ is 0.978 atm, so, let's write an ICE chart and see what's happening here:

                 2NH₃(g) <> 3H₂(g) + N₂(g)

i)                     y                      0           0

c)                 -2x                   +3x          x

e)                y-2x                    3x          x

At the beggining we just have the sample of NH₃, we don't know how much but we don't need that data to get the partial pressure. In equilibrium, its produced hydrogen and nitrogen, and we know how much of hydrogen was produced, so, with that we can solve for the value of the partial pressure of NO by a simple math operation:

PpH₂ = 0.978 atm = 3x

PpN₂ = x

PpN₂ = PpH₂ / 3

PpN₂ = 0.978 / 3

Hope this helps