We’re being asked to calculate molar mass of gas Y if it effuses half as fast as O2.
Recall that Graham's Law of Effusion allows us to compare the rate of effusion of two gases. Graham's Law states that the rate of effusion of a gas is inversely proportional to its molar mass.
This means that when comparing two gases:
Let's designate O2 as gas 2 and the gas Y as gas 1.
rate gas Y = 0.5 (rate O2)
The molar mass of O2 is:
O2 2 O × 16 g/mol O = 32 g/mol
Sum = 32 g/mol
Gas Y effuses half as fast as O2. What is the molar mass of gas Y?