Question

a vessel contains equal mass of methane and helium gases at 120degree Celsius and 800 mm Hg pressure . What is the partial pressure of methane​

Answer 1

Given info : A vessel contains equal mass of methane and helium gases at 120°C and 800 mm Hg pressure.

To find : the partial pressure of methane is ....

solution : let the mass of methane or helium gas is m

no of moles of methane = mass of methane/molar mass of methane

                                        = m/16

no of moles of helium = mass of helium/atomic mass of helium

                                    = m/4

now the mole fraction of methane = no of moles of methane/ (no of moles of methane + no of moles of helium)

= (m/16)/(m/16 + m/4)

= 1/5 = 0.2

according to Dalton's law of the partial pressure, the partial pressure of each non reactive gas is the product of mole fraction of the gas and the total pressure of gases.

i.e., partial pressure = mole fraction × total pressure

∴ partial pressure of methane = mole fraction of methane × total pressure

                                                  = 0.2 × 800 mm Hg

                                                  = 160 mm Hg

therefore the partial pressure of methane is 160 mm Hg and the the partial pressure of helium gas is 800 - 160 = 640 mm Hg.