If a gas with a pressure of 5 atmospheres cooled from 500 k to 250 k, then what is its final pressure?

Solution is here,

initial pressure(P1)=5 atm

initial temperature(T1)=500K

final pressure(P2)=?

final temperature(T2)=250K

now from Charle' law of gas,

P1/P2 =T1/T2

or, 5/P2 =500/250

or, 5/P2 = 2

or, P2=5/2

or, P2=2.5 atm

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.