# Given the weight composition, compute the partial pressures

• Chemistry
• DottZakapa

#### DottZakapa

Homework Statement
a reactor contains a gas mixture of nitrogen, oxygen and propane at a total pressure of 5.00 atm. The weight composition of the mixture is 56 % nitrogen 32% oxygen 12% propane.calculate the partial pressures of the three gases.
Relevant Equations
gas laws
Hi can someone give an hand on understanding how to handle such kind of problems ?
can't come up with a valid solution.
if i do
##\frac {0,56}{2*14.00}## do i get the molar fraction of nitrogen?

Last edited by a moderator:
ok finally got inspired.

##n_{N_2}=\frac {56}{2*14.00} = 2## mol
##n_{O_2}=\frac {32}{2*16.00} = 1##mol
##n_{C_3H_8}=\frac {12}{(3*12.01)+(8*1.01)}=0.2720## mol

In order to find the molar fraction:

##n_{tot}=n_{N_2}+n_{O_2}+n_{C_3H_8}##

##\chi_{N_2}=\frac {n_{N_2}}{n_{tot}} ##

##\chi_{O_2}=\frac {n_{O_2}}{n_{tot}} ##

##\chi_{C_3H_8}=\frac {n_{C_3H_8}}{n_{tot}} ##

In order to compute the partial pressures:

##P_{N_2}= \chi_{N_2} P_{tot}##

##P_{O_2}= \chi_{O_2} P_{tot}##

##P_{C_3H_8}= \chi_{C_3H_8} P_{tot}##

And this solves the problem

• Chestermiller
Looks correct. Remember units when calculating amount of substance.