A cylinder of compressed gas is labeled Composition (mole %): 4.5% H2S, 3.0% CO2, balance N2. The pressure gauge attached to the cylinder reads 46 atm. Calculate the partial pressure of each gas, in atmospheres, in the cylinder.

p (H₂S) =    2.07 atm

p (CO₂) =    1.38 atm

p (N₂)    = 42.55 atm

Explanation:

We can solve this question by remembering that the partial pressure of a gas is given by the product of its mole fraction times the total pressure.

In this question we have the total pressure, and the concentration in mol percent and it will be easy to compute the mol fraction, X,  by:

1 . Assume one hundred  total mol of gas

2. X (A) = number of mol of A/total number of moles

So,

X (H₂S) = 4.5 mol / 100 mol = 0.045

and similarly for the rest of the gases:

X (CO₂) = 0.03

X (N₂) = 100 - ( 0.045 + 0.03) = 0.925

The partial pressures finally are:

p (H₂S) = 0.045 x 46 atm = 2.07 atm

p (CO₂) = 0.03 x 46 atm = 1.38 atm

p(N₂) = 0.925 x 46 atm = 42.55 atm