# PCHEM/Partial Pressures Question

1. Sep 11, 2007

### Coffeepower

[SOLVED] PCHEM/Partial Pressures Question

Problem Statement:
A vessel of volume 22.4dm$$^{}3$$ contains 2.0 mol H$$_{}2$$ and 1.0 mol of N$$_{}2$$ at 273.15K initially. All the H$$_{}2$$reacted with sufficient N$$_{}2$$ to form NH$$_{}3$$. Calculate the partial pressures and the total pressure of the final mixture.

Variables and Magnitudes:
V = 22.4dm$$^{}3$$
T = 273.15K
n$$_{}H_{}2$$= 2.0 mol
n$$_{}N_{}2$$= 1.0 mol

First Attempt:
2H$$_{}2$$+N$$_{}2$$$$\rightarrow$$NH$$_{}3$$
It takes 1.5 mol of H$$_{}2$$ to make 1 mol of NH$$_{}3$$ so I was thinking that I should say that:

p$$_{}H_{}2$$ = p$$_{}total$$*X$$_{}H_{}2$$ = ?

We would need to calculate the total pressure first for this.

I need a place to start this problem. I just can't put my finger on it.

2. Sep 13, 2007

### Coffeepower

After working on the problem some more; I found that there is a simple way to do the problem. Simply find the mole fractions with the number of moles given and calculate the total pressure with PV = nRT for 3 moles, and 22.4dm^3.

Not much more to it than that. The solution in the book matches up.