A 1.00 L gas sample at 100. degrees Celsius and 600. torr contains 50.0% helium and 50.0% xenon by mass. What are the

Question

A 1.00 L gas sample at 100. degrees Celsius and 600. torr contains 50.0% helium and 50.0% xenon by mass. What are the partial pressures of the individual gases

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Solution
Note that
The partial pressure of a gas is equal to its mole fraction times the total pressure

First calculate the total number of mole using ideal gas law:

Here P = 600 torr = 0.789 atm
R = 0.0821 L atm/mol K
T = 100+273 = 373 (K)
Hence the total number of mole is:

Molecular weights of He and Xe are 4 and 131 g/mol, respectively.
Let n1 and n2 be the number of mole of He and Xe, we can write:
n = 0.0258 = n1+ n2
Also in terms of mass, the sample contains 50.0% helium and 50.0% xenon. Thus,

Hence n1 = 0.1/4 = 0.025 (mol of He)
n2 = 0.1/131 = 0.0008 (mol of Xe)
Thus the partial pressures are: