Question

15.00g of ammonium nitrate decomposes into an expandable container acoording to the following equation.
2NH4NO3 ==> 2N2 g + 4H2O g + O2 g

which has the highest partial pressure
a. N2
b. H2O
c. O2

i am not sure how to approach this problem. is there a simple way to solve this . i noticed that if i divided the amount of mols for each gas by its molar mass that H20 has a greater mass, can this relate to the answer. thank you in advance

Answer 1

I think you have lucked onto the right answer but not the right reasoning. Two ways to look at it.
First way. PV = nRT. V,R,T are constant(k) so pressure = k(n)
So more mols the higher P; therefore, we go with water.

Second way. Since the balloon is expandable, the end pressure will be atmospheric pressure. Let's call that 760 mm. Then
pgas = Xgas*Ptotal.
Since Ptotal is the same for all of them, then pgas = k*X; therefore, the one with the largest mol fraction will have the highest partial pressure.
Total mols is 7 so
XN2 = 2/7
XH2O = 4/7
XO2 = 1/7.
Again, H2O is the one.