Chemistry partial pressure

Question

if we place 2.00g of oxygen and 4.00g of methane gas in a 1.00L container at 50C, what would be the total pressure?

Answer 1

Convert g to moles:

2.00 g O₂ x 1 mol O2/32 g = 0.0625 moles O₂

4.00 g CH₄ x 1 mol CH4/16 g = 0.250 moles CH₄

Total moles of gas = 0.3125 moles of gas

Find the total pressure using ideal gas law:

PV = nRT

P = nRT/V = (0.3125 mol)(0.0821 Latm/Kmol)(323K) / 1.00 L

P = 8.287 atm = total pressure

Mole fraction of O₂ = 0.0625 mol / 0.3125 moles = 0.2

Mole fraction of CH₄ = 0.250/0.3125 = 0.8

Partial pressure of O₂ = 0.2 x 8.287 atm = 1.66 atm

Partial pressure of CH₄ = 0.8 x 8.287 atm = 6.63 atm

NOTE: You can also do this by applying PV = nRT for each gas separately, adding the pressures together to get P_total and then find partial pressures that way.